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Arthropod-borne viruses (arboviruses) are transmitted to humans primarily through the bites of infected mosquitoes and ticks. West Nile virus (WNV) is the leading cause of domestically acquired arboviral disease in the United States (1). Other arboviruses, including La Crosse, Jamestown Canyon, Powassan, eastern equine encephalitis, and St. Louis encephalitis viruses, cause sporadic disease and occasional outbreaks. This report summarizes surveillance data for nationally notifiable domestic arboviruses reported to CDC for 2019. For 2019, 47 states and the District of Columbia (DC) reported 1,173 cases of domestic arboviral disease, including 971 (83%) WNV disease cases. Among the WNV disease cases, 633 (65%) were classified as neuroinvasive disease, for a national incidence of 0.19 cases per 100,000 population, 53% lower than the median annual incidence during 2009-2018. More Powassan and eastern equine encephalitis virus disease cases were reported in 2019 than in any previous year. Health care providers should consider arboviral infections in patients with aseptic meningitis or encephalitis, perform recommended diagnostic testing, and promptly report cases to public health authorities. Because arboviral diseases continue to cause serious illness, and annual incidence of individual viruses continues to vary with sporadic outbreaks, maintaining surveillance is important in directing prevention activities. Prevention depends on community and household efforts to reduce vector populations and personal protective measures to prevent mosquito and tick bites such as use of Environmental Protection Agency-registered insect repellent and wearing protective clothing.*,†.

West Nile virus (WNV) is a mosquito-borne flavivirus that can cause severe neurological disease in humans, for which there is no treatment or vaccine. From 2009 to 2018, California has reported more human disease cases than any other state in the United States. We sought to identify smaller geographic areas within the 10 California counties with the highest number of WNV cases that accounted for disproportionately large numbers of human cases from 2009 to 2018. Eleven areas, consisting of groups of high-burden ZIP codes, were identified in nine counties within southern California and California's Central Valley. Despite containing only 2% of California's area and 17% of the state's population, these high-burden ZIP codes accounted for 44% of WNV cases reported and had a mean annual incidence that was 2.4 times the annual state incidence. Focusing mosquito control and public education efforts in these areas would lower WNV disease burden.

Problem/condition West Nile virus (WNV) is an arthropodborne virus (arbovirus) in the family Flaviviridae and is the leading cause of domestically acquired arboviral disease in the contiguous United States. An estimated 70%-80% of WNV infections are asymptomatic. Symptomatic persons usually develop an acute systemic febrile illness. Less than 1% of infected persons develop neuroinvasive disease, which typically presents as encephalitis, meningitis, or acute flaccid paralysis. Reporting period 2009-2018. Description of system WNV disease is a nationally notifiable condition with standard surveillance case definitions. State health departments report WNV cases to CDC through ArboNET, an electronic passive surveillance system. Variables collected include patient age, sex, race, ethnicity, county and state of residence, date of illness onset, clinical syndrome, hospitalization, and death. Results During 2009-2018, a total of 21,869 confirmed or probable cases of WNV disease, including 12,835 (59%) WNV neuroinvasive disease cases, were reported to CDC from all 50 states, the District of Columbia, and Puerto Rico. A total of 89% of all WNV patients had illness onset during July-September. Neuroinvasive disease incidence and case-fatalities increased with increasing age, with the highest incidence (1.22 cases per 100,000 population) occurring among persons aged ≥70 years. Among neuroinvasive cases, hospitalization rates were >85% in all age groups but were highest among patients aged ≥70 years (98%). The national incidence of WNV neuroinvasive disease peaked in 2012 (0.92 cases per 100,000 population). Although national incidence was relatively stable during 2013-2018 (average annual incidence: 0.44; range: 0.40-0.51), state level incidence varied from year to year. During 2009-2018, the highest average annual incidence of neuroinvasive disease occurred in North Dakota (3.16 cases per 100,000 population), South Dakota (3.06), Nebraska (1.95), and Mississippi (1.17), and the largest number of total cases occurred in California (2,819), Texas (2,043), Illinois (728), and Arizona (632). Six counties located within the four states with the highest case counts accounted for 23% of all neuroinvasive disease cases nationally. Interpretation Despite the recent stability in annual national incidence of neuroinvasive disease, peaks in activity were reported in different years for different regions of the country. Variations in vectors, avian amplifying hosts, human activity, and environmental factors make it difficult to predict future WNV disease incidence and outbreak locations. Public health action WNV disease surveillance is important for detecting and monitoring seasonal epidemics and for identifying persons at increased risk for severe disease. Surveillance data can be used to inform prevention and control activities. Health care providers should consider WNV infection in the differential diagnosis of aseptic meningitis and encephalitis, obtain appropriate specimens for testing, and promptly report cases to public health authorities. Public health education programs should focus prevention messaging on older persons, because they are at increased risk for severe neurologic disease and death. In the absence of a human vaccine, WNV disease prevention depends on community-level mosquito control and household and personal protective measures. Understanding the geographic distribution of cases, particularly at the county level, appears to provide the best opportunity for directing finite resources toward effective prevention and control activities. Additional work to further develop and improve predictive models that can foreshadow areas most likely to be impacted in a given year by WNV outbreaks could allow for proactive targeting of interventions and ultimately lowering of WNV disease morbidity and mortality.

Two coronavirus disease 2019 (COVID-19) vaccines are currently authorized for use in the United States. The Food and Drug Administration (FDA) issued Emergency Use Authorization (EUA) for the Pfizer-BioNTech COVID-19 vaccine on December 11, 2020, and for the Moderna COVID-19 vaccine on December 18, 2020; each is administered as a 2-dose series. The Advisory Committee on Immunization Practices issued interim recommendations for Pfizer-BioNTech and Moderna COVID-19 vaccines on December 12, 2020 (1), and December 19, 2020 (2), respectively; initial doses were recommended for health care personnel and long-term care facility (LTCF) residents (3). Safety monitoring for these vaccines has been the most intense and comprehensive in U.S. history, using the Vaccine Adverse Event Reporting System (VAERS), a spontaneous reporting system, and v-safe,* an active surveillance system, during the initial implementation phases of the COVID-19 national vaccination program (4). CDC conducted descriptive analyses of safety data from the first month of vaccination (December 14, 2020-January 13, 2021). During this period, 13,794,904 vaccine doses were administered, and VAERS received and processed† 6,994 reports of adverse events after vaccination, including 6,354 (90.8%) that were classified as nonserious and 640 (9.2%) as serious.§ The symptoms most frequently reported to VAERS were headache (22.4%), fatigue (16.5%), and dizziness (16.5%). A total of 113 deaths were reported to VAERS, including 78 (65%) among LTCF residents; available information from death certificates, autopsy reports, medical records, and clinical descriptions from VAERS reports and health care providers did not suggest any causal relationship between COVID-19 vaccination and death. Rare cases of anaphylaxis after receipt of both vaccines were reported (4.5 reported cases per million doses administered). Among persons who received Pfizer-BioNTech vaccine, reactions reported to the v-safe system were more frequent after receipt of the second dose than after the first. The initial postauthorization safety profiles of the two COVID-19 vaccines in current use did not indicate evidence of unexpected serious adverse events. These data provide reassurance and helpful information regarding what health care providers and vaccine recipients might expect after vaccination.

Arthropod-borne viruses (arboviruses) are transmitted to humans primarily through the bite of infected mosquitoes and ticks. West Nile virus (WNV), mainly transmitted by Culex species mosquitos, is the leading cause of domestically acquired arboviral disease in the United States (1). Other arboviruses cause sporadic cases of disease and occasional outbreaks. This report summarizes passive data for nationally notifiable domestic arboviruses in the United States reported to CDC for 2020. Forty-four states reported 884 cases of domestic arboviral disease, including those caused by West Nile (731), La Crosse (88), Powassan (21), St. Louis encephalitis (16), eastern equine encephalitis (13), Jamestown Canyon (13), and unspecified California serogroup (2) viruses. A total of 559 cases of neuroinvasive WNV disease were reported, for a national incidence of 0.17 cases per 100,000 population. Because arboviral diseases continue to cause serious illness and the locations of outbreaks vary annually, health care providers should consider arboviral infections in patients with aseptic meningitis or encephalitis that occur during periods when ticks and mosquitoes are active, perform recommended diagnostic testing, and promptly report cases to public health authorities to guide prevention strategies and messaging.

Most diagnostic testing for West Nile virus (WNV) disease is accomplished using serologic testing, which is subject to cross-reactivity, may require cumbersome confirmatory testing, and may fail to detect infection in specimens collected early in the course of illness. The objective of this project was to determine whether a combination of molecular and serologic testing would increase detection of WNV disease cases in acute serum samples. A total of 380 serum specimens collected ≤7 days after onset of symptoms and submitted to four state public health laboratories for WNV diagnostic testing in 2014 and 2015 were tested. WNV immunoglobulin M (IgM) antibody and RT-PCR tests were performed on specimens collected ≤3 days after symptom onset. WNV IgM antibody testing was performed on specimens collected 4–7 days after onset and RT-PCR was performed on IgM-positive specimens. A patient was considered to have laboratory evidence of WNV infection if they had detectable WNV IgM antibodies or WNV RNA in the submitted serum specimen. Of specimens collected ≤3 days after symptom onset, 19/158 (12%) had laboratory evidence of WNV infection, including 16 positive for only WNV IgM antibodies, 1 positive for only WNV RNA, and 2 positive for both. Of specimens collected 4–7 days after onset, 21/222 (9%) were positive for WNV IgM antibodies; none had detectable WNV RNA. These findings suggest that routinely performing WNV RT-PCR on acute serum specimens submitted for WNV diagnostic testing is unlikely to identify a substantial number of additional cases beyond IgM antibody testing alone.

Arthropodborne viruses (arboviruses) are transmitted to humans primarily through the bites of infected mosquitoes and ticks. West Nile virus (WNV) is the leading cause of domestically acquired arboviral disease in the continental United States (1). Other arboviruses, including eastern equine encephalitis, Jamestown Canyon, La Crosse, Powassan, and St. Louis encephalitis viruses, cause sporadic cases of disease and occasional outbreaks. This report summarizes surveillance data reported to CDC for 2018 on nationally notifiable arboviruses. It excludes dengue, chikungunya, and Zika viruses because they are primarily nondomestic viruses typically acquired through travel. In 2018, 48 states and the District of Columbia (DC) reported 2,813 cases of domestic arboviral disease, including 2,647 (94%) WNV disease cases. Of the WNV disease cases, 1,658 (63%) were classified as neuroinvasive disease (e.g., meningitis, encephalitis, and acute flaccid paralysis), for a national incidence of 0.51 cases of WNV neuroinvasive disease per 100,000 population. Because arboviral diseases continue to cause serious illness and have no definitive treatment, maintaining surveillance is important to direct and promote prevention activities. Health care providers should consider arboviral infections in patients with aseptic meningitis or encephalitis, perform appropriate diagnostic testing, and report cases to public health authorities.

La Crosse virus (LACV) is an arthropod-borne virus that can cause a nonspecific febrile illness, meningitis, or encephalitis. We reviewed U.S. LACV surveillance data for 2003–2019, including human disease cases and nonhuman infections. Overall, 318 counties in 27 states, principally in the Great Lakes, mid-Atlantic, and southeastern regions, reported LACV activity. A total of 1,281 human LACV disease cases were reported, including 1,183 (92%) neuroinvasive disease cases. The median age of cases was 8 years (range: 1 month–95 years); 1,130 (88%) were aged < 18 years, and 754 (59%) were male. The most common clinical syndromes were encephalitis (N = 960; 75%) and meningitis (N = 219, 17%). The case fatality rate was 1% (N = 15). A median of 74 cases (range: 35–130) was reported per year. The average annual national incidence of neuroinvasive disease cases was 0.02 per 100,000 persons. West Virginia, North Carolina, Tennessee, and Ohio had the highest average annual state incidences (0.16–0.61 per 100,000), accounting for 80% (N = 1,030) of cases. No animal LACV infections were reported. Nine states reported LACV-positive mosquito pools, including three states with no reported human disease cases. La Crosse virus is the most common cause of pediatric neuroinvasive arboviral disease in the United States. However, surveillance data likely underestimate LACV disease incidence. Healthcare providers should consider LACV disease in patients, especially children, with febrile illness, meningitis, or encephalitis in areas where the virus circulates and advise their patients on ways to prevent mosquito bites.

Arthropodborne viruses (arboviruses) are transmitted to humans primarily through the bites of infected mosquitoes or ticks. West Nile virus (WNV) is the leading cause of domestically acquired arboviral disease in the continental United States (1). Other arboviruses, including Jamestown Canyon, La Crosse, Powassan, St. Louis encephalitis, and eastern equine encephalitis viruses, cause sporadic cases of disease and occasional outbreaks. This report summarizes surveillance data reported to CDC from U.S. states in 2017 for nationally notifiable arboviruses. It excludes dengue, chikungunya, and Zika viruses because, in the continental United States, these viruses are acquired primarily through travel. In 2017, 48 states and the District of Columbia (DC) reported 2,291 cases of domestic arboviral disease, including 2,097 (92%) WNV disease cases. Among the WNV disease cases, 1,425 (68%) were classified as neuroinvasive disease (e.g., meningitis, encephalitis, or acute flaccid paralysis), for a national rate of 0.44 cases per 100,000 population. More Jamestown Canyon and Powassan virus disease cases were reported in 2017 than in any previous year. Because arboviral diseases continue to cause serious illness, maintaining surveillance is important to direct and promote prevention activities.

Introduction Vectorborne diseases are major causes of death and illness worldwide. In the United States, the most common vectorborne pathogens are transmitted by ticks or mosquitoes, including those causing Lyme disease; Rocky Mountain spotted fever; and West Nile, dengue, and Zika virus diseases. This report examines trends in occurrence of nationally reportable vectorborne diseases during 2004-2016. Methods Data reported to the National Notifiable Diseases Surveillance System for 16 notifiable vectorborne diseases during 2004-2016 were analyzed; findings were tabulated by disease, vector type, location, and year. Results A total 642,602 cases were reported. The number of annual reports of tickborne bacterial and protozoan diseases more than doubled during this period, from >22,000 in 2004 to >48,000 in 2016. Lyme disease accounted for 82% of all tickborne disease reports during 2004-2016. The occurrence of mosquitoborne diseases was marked by virus epidemics. Transmission in Puerto Rico, the U.S. Virgin Islands, and American Samoa accounted for most reports of dengue, chikungunya, and Zika virus diseases; West Nile virus was endemic, and periodically epidemic, in the continental United States. Conclusions and implications for public health practice Vectorborne diseases are a large and growing public health problem in the United States, characterized by geographic specificity and frequent pathogen emergence and introduction. Differences in distribution and transmission dynamics of tickborne and mosquitoborne diseases are often rooted in biologic differences of the vectors. To effectively reduce transmission and respond to outbreaks will require major national improvement of surveillance, diagnostics, reporting, and vector control, as well as new tools, including vaccines.

Arthropod-borne viruses (arboviruses) are transmitted to humans primarily through the bites of infected mosquitoes and ticks. West Nile virus (WNV) is the leading cause of domestically acquired arboviral disease in the continental United States (1,2). Other arboviruses, including La Crosse, Powassan, Jamestown Canyon, St. Louis encephalitis, and eastern equine encephalitis viruses, cause sporadic cases of disease and occasional outbreaks. This report summarizes surveillance data reported to CDC for 2016 for nationally notifiable arboviruses. It excludes dengue, chikungunya, and Zika viruses, as these are primarily nondomestic viruses typically acquired through travel. Forty-seven states and the District of Columbia (DC) reported 2,240 cases of domestic arboviral disease, including 2,150 (96%) WNV disease cases. Of the WNV disease cases, 1,310 (61%) were classified as neuroinvasive disease (e.g., meningitis, encephalitis, acute flaccid paralysis), for a national incidence of 0.41 cases per 100,000 population. After WNV, the most frequently reported arboviruses were La Crosse (35 cases), Powassan (22), and Jamestown Canyon (15) viruses. Because arboviral diseases continue to cause serious illness, maintaining surveillance is important to direct prevention activities.

Chikungunya virus is a mosquito-borne alphavirus that causes an acute febrile illness with severe polyarthralgia. The first local transmission of chikungunya virus in the Western Hemisphere was reported in December 2013. In the following year, the virus spread throughout much of the Americas and the number of cases among travelers increased substantially. We reviewed the epidemiology of chikungunya virus disease cases reported among U.S. travelers from 2014 to 2016. A total of 3,941 travel-acquired cases were reported from 49 states and the District of Columbia; 3,616 (92%) reported travel to other countries or territories in the Americas; the remaining 8% reported travel to Asia, Africa, or the Western Pacific. The most commonly reported travel destinations were the Dominican Republic, Puerto Rico, and Haiti. The largest number of cases (N = 2,780, 71%) had illness onset in 2014, followed by 2015 (N = 913, 23%) and 2016 (N = 248, 6%). Cases occurred in every month, but 70% of case-patients had illness onset from April to September, the months when mosquitoes are most likely to be active in the continental United States. Travel-acquired chikungunya cases will likely continue to occur and present a risk of introduction of the virus to locations in the continental United States. Clinicians and public health officials should be educated about the recognition, diagnosis, management, and timely reporting of chikungunya cases.

Dengue, chikungunya, and Zika viruses, primarily transmitted by Aedes species mosquitoes, have caused large outbreaks in the Americas, leading to travel-associated cases and local mosquito-borne transmission in the United States. We describe the epidemiology of dengue, chikungunya, and noncongenital Zika virus disease cases reported from U.S. states and territories in 2017, including 971 dengue cases, 195 chikungunya cases, and 1,118 Zika virus disease cases. Cases of all three diseases reported from the territories were reported as resulting from local mosquito-borne transmission. Cases reported from the states were primarily among travelers, with only seven locally acquired mosquito-transmitted Zika virus disease cases reported from Texas (n = 5) and Florida (n = 2). In the territories, most dengue cases (n = 508, 98%) were reported from American Samoa, whereas the majority of chikungunya (n = 39, 100%) and Zika virus disease (n = 620, 93%) cases were reported from Puerto Rico. Temporally, the highest number of Zika virus disease cases occurred at the beginning of the year, followed by a sharp decline, mirroring decreasing case numbers across the Americas following large outbreaks in 2015 and 2016. Dengue and chikungunya cases followed a more seasonal pattern, with higher case numbers from July through September. Travelers to the United States and residents of areas with active virus transmission should be informed of both the ongoing risk from dengue, chikungunya, and Zika virus disease and personal protective measures to lower their risk of mosquito bites and to help prevent the spread of these diseases.

In 2013, the national surveillance case definition for West Nile virus (WNV) disease was revised to remove fever as a criterion for neuroinvasive disease and require at most subjective fever for non-neuroinvasive disease. The aims of this project were to determine how often afebrile WNV disease occurs and assess differences among patients with and without fever. We included cases with laboratory evidence of WNV disease reported from four states in 2014. We compared demographics, clinical symptoms and laboratory evidence for patients with and without fever and stratified the analysis by neuroinvasive and non-neuroinvasive presentations. Among 956 included patients, 39 (4%) had no fever; this proportion was similar among patients with and without neuroinvasive disease symptoms. For neuroinvasive and non-neuroinvasive patients, there were no differences in age, sex, or laboratory evidence between febrile and afebrile patients, but hospitalisations were more common among patients with fever (P < 0.01). The only significant difference in symptoms was for ataxia, which was more common in neuroinvasive patients without fever (P = 0.04). Only 5% of non-neuroinvasive patients did not meet the WNV case definition due to lack of fever. The evidence presented here supports the changes made to the national case definition in 2013.

BackgroundThe clinical findings among children with postnatally acquired Zika virus disease are not well characterized. We describe and compare clinical signs and symptoms for children aged MethodsZika virus disease cases were included if they met the national surveillance case definition, had illness onset in 2016 or 2017, resided in a participating state, and were reported to the Centers for Disease Control and Prevention. Pediatric cases were aged ResultsA total of 141 pediatric Zika virus disease cases were identified; none experienced neurologic disease. Overall, 28 (20%) were treated in an emergency department, 1 (ConclusionsThis report supports previous findings that Zika virus disease is generally mild in children. The most common symptoms are similar to other childhood infections, and clinical findings and outcomes are similar to those in adults. Healthcare providers should consider a diagnosis of Zika virus infection in children with fever, rash, arthralgia, or conjunctivitis, who reside in or have traveled to an area where Zika virus transmission is occurring.

We estimated the seroprevalence of Heartland virus antibodies to be 0.9% (95% CI 0.4%–4.2%) in a convenience sample of blood donors from northwestern Missouri, USA, where human cases and infected ticks have been identified. Although these findings suggest that some past human infections were undetected, the estimated prevalence is low.

Background Few studies have assessed the duration of humoral immunity following yellow fever (YF) vaccination in a non-endemic population. We evaluated seropositivity among US resident travellers based on time post-vaccination. Methods We identified serum samples from US travellers with YF virus-specific plaque reduction neutralization testing (PRNT) performed at CDC from 1988 to 2016. Analyses were conducted to assess the effect of time since vaccination on neutralizing antibody titer counts. Results Among 234 travellers who had neutralizing antibody testing performed on a specimen obtained ≥1 month after vaccination, 13 received multiple YF vaccinations and 221 had one dose of YF vaccine reported. All 13 who received more than one dose of YF vaccine had a positive PRNT regardless of the amount time since most recent vaccination. Among the 221 travellers with one reported dose of YF vaccine, 155 (70%) were vaccinated within 10 years (range 1 month-9 years) and 66 (30%) were vaccinated ≥10 years (range 10-53 years) prior to serum collection. Among the 155 individuals vaccinated

St. Louis encephalitis virus (SLEV), an arthropod-borne flavivirus, can cause disease presentations ranging from mild febrile illness through severe encephalitis. We reviewed U.S. national SLEV surveillance data for 2003 through 2017, including human disease cases and nonhuman infections. Over the 15-year period, 198 counties from 33 states and the District of Columbia reported SLEV activity; 94 (47%) of those counties reported SLEV activity only in nonhuman species. A total of 193 human cases of SLEV disease were reported, including 148 cases of neuroinvasive disease. A median of 10 cases were reported per year. The national average annual incidence of reported neuroinvasive disease cases was 0.03 per million. States with the highest average annual incidence of reported neuroinvasive disease cases were Arkansas, Arizona, and Mississippi. No large outbreaks occurred during the reporting period. The most commonly reported clinical syndromes were encephalitis (N = 116, 60%), febrile illness (N = 35, 18%), and meningitis (N = 25, 13%). Median age of cases was 57 years (range 2-89 years). The case fatality rate was 6% (11/193) and all deaths were among patients aged > 45 years with neuroinvasive disease. Nonhuman surveillance data indicated wider SLEV activity in California, Nevada, and Florida than the human data alone suggested. Prevention depends on community efforts to reduce mosquito populations and personal protective measures to decrease exposure to mosquitoes.

BACKGROUND: Powassan virus (POWV) is a tick-borne flavivirus that causes rare, but often severe, disease in humans. POWV neuroinvasive disease was added to the U.S. nationally notifiable disease list in 2001 and non-neuroinvasive disease was added in 2004. The only previous review of the epidemiology of POWV disease in the United States based on cases reported to the Centers for Disease Control and Prevention (CDC) covered the period from 1999 through 2005. METHODS: We describe the epidemiology and clinical features of laboratory-confirmed POWV disease cases reported to CDC from 2006 through 2016. RESULTS: There were 99 cases of POWV disease reported during the 11-year period, including 89 neuroinvasive and 10 non-neuroinvasive disease cases. There was a median of 7 cases per year (range: 1–22), with the highest numbers of cases reported in 2011 (n=16), 2013 (n=15) and 2016 (n=22). Cases occurred throughout the year but peaked in May and June. Cases were reported primarily from northeastern and north-central states. Overall, 72 (73%) cases were in males and the median age was 62 years (range: 3 months – 87 years). Of the 11 (11%) cases who died, all were aged >50 years. The average annual incidence of neuroinvasive POWV disease was 0.0025 cases per 100,000 persons. CONCLUSIONS: POWV disease can be a severe disease and has been diagnosed with increased frequency in recent years. However, this might reflect increased disease awareness, improved test availability, and enhanced surveillance efforts. Clinicians should consider POWV disease in patients presenting with acute encephalitis or aseptic meningitis who are resident in, or have traveled to, an appropriate geographic region.

Zika virus is a flavivirus primarily transmitted to humans by Aedes aegypti mosquitoes (1). Zika virus infections also have been documented through intrauterine transmission resulting in congenital infection; intrapartum transmission from a viremic mother to her newborn; sexual transmission; blood transfusion; and laboratory exposure (1-3). Most Zika virus infections are asymptomatic or result in mild clinical illness, characterized by acute onset of fever, maculopapular rash, arthralgia, or nonpurulent conjunctivitis; Guillain-Barre syndrome, meningoencephalitis, and severe thrombocytopenia rarely have been associated with Zika virus infection (1). However, congenital Zika virus infection can result in fetal loss, microcephaly, and other birth defects (1,2). In 2016, a total of 5,168 noncongenital Zika virus disease cases were reported from U.S. states and the District of Columbia. Most cases (4,897, 95%) were in travelers returning from Zika virus-affected areas. A total of 224 (4%) cases were acquired through presumed local mosquitoborne transmission, and 47 (1%) were acquired by other routes. It is important that providers in the United States continue to test symptomatic patients who live in or recently traveled to areas with ongoing Zika virus transmission or had unprotected sex with someone who lives in or traveled to those areas. All pregnant women and their partners should take measures to prevent Zika virus infection during pregnancy. A list of affected areas and specific recommendations on how to prevent Zika virus infection during pregnancy are available at https://www.cdc.gov/pregnancy/zika/protect-yourself.html.

Arthropod-borne viruses (arboviruses) are transmitted to humans primarily through the bites of infected mosquitoes and ticks. West Nile virus (WNV) is the leading cause of domestically acquired arboviral disease in the United States (1). However, several other arboviruses also cause sporadic cases and seasonal outbreaks. This report summarizes surveillance data reported to CDC in 2014 for WNV and other nationally notifiable arboviruses, excluding dengue. Forty-two states and the District of Columbia (DC) reported 2,205 cases of WNV disease. Of these, 1,347 (61%) were classified as WNV neuroinvasive disease (e.g., meningitis, encephalitis, or acute flaccid paralysis), for a national incidence of 0.42 cases per 100,000 population. After WNV, the next most commonly reported cause of arboviral disease was La Crosse virus (80 cases), followed by Jamestown Canyon virus (11), St. Louis encephalitis virus (10), Powassan virus (8), and Eastern equine encephalitis virus (8). WNV and other arboviruses cause serious illness in substantial numbers of persons each year. Maintaining surveillance programs is important to help direct prevention activities.

Infection with La Crosse virus can cause meningoencephalitis, but it is not known to cause acute flaccid paralysis (AFP). During 2008-2014, nine confirmed or probable La Crosse virus disease cases with possible AFP were reported in Ohio, USA. After an epidemiologic and clinical investigation, we determined no patients truly had AFP.

Background Japanese encephalitis (JE) is a mosquito-borne disease that is associated with considerable morbidity and mortality in many Asian countries. The objective of this study was to describe the impact of the JE immunization program using SA 14-14-2 JE vaccine implemented in Nepal during 2006 through 2011. A previous assessment after the initial program implementation phase described a significantly lower post-campaign JE incidence compared to expected incidence; however, the previous evaluation had limited post-campaign data for some districts. Methodology/Principal findings JE and acute encephalitis syndrome (AES) data gathered through Nepal’s routine surveillance system from 2004 through 2014 were analyzed to assess the impact of the JE immunization program implemented in 31 districts. Expected incidence rates were determined by calculating the incidence of cases per 100,000 person-years in each district before the vaccination campaigns. This rate was applied to the relevant population after the vaccination campaigns, which provided the expected number of cases had the campaign not occurred. The observed incidence rate was the number of reported cases per 100,000 person-years post-campaign. Expected and observed JE and AES cases and incidence rates were compared. The post-campaign JE incidence rate of 0.7 cases per 100,000 was 78% (95% CI 76%–79%) lower than expected had no campaign occurred and an estimated 3,011 (95% CI 2,941–3,057) JE cases were prevented. The post-vaccination AES incidence of 5.5 cases per 100,000 was 59% (58%–60%) lower than the expected and an estimated 9,497 (95% CI 9,268–9,584) AES cases were prevented. Conclusions/Significance This analysis strengthens previous findings of the substantial impact of Nepal’s JE immunization program using SA 14-14-2 JE vaccine., Author summary In 2006, the Ministry of Health and Population in Nepal commenced a Japanese encephalitis (JE) immunization program using SA 14-14-2 JE vaccine, with mass campaigns conducted in selected districts, followed by introduction of JE vaccine into the routine childhood immunization program. JE and acute encephalitis syndrome data gathered through Nepal’s routine surveillance system from 2004 through 2014 were analyzed to assess the impact of this immunization program. Expected and observed JE and acute encephalitis syndrome cases and incidence rates were compared. Considerable impact on JE incidence was demonstrated and the results also suggested that a large proportion of acute encephalitis syndrome cases without laboratory confirmation are due to JE. The results support the belief that a JE immunization program will result in sizable reductions in the incidence of both laboratory-confirmed JE and clinical acute encephalitis syndrome cases. JE is a severe disease, and the program’s impact likely extended to reduction of rates of JE-related mortality and long-term disability.

Cross-reactivity within flavivirus antibody assays, produced by shared epitopes in the envelope proteins, can complicate the serological diagnosis of Zika virus (ZIKAV) infection. We assessed the utility of the plaque reduction neutralization test (PRNT) to confirm recent ZIKAV infections and rule out misleading positive immunoglobulin M (IgM) results in areas with various levels of past dengue virus (DENV) infection incidence. We reviewed PRNT results of sera collected for diagnosis of ZIKAV infection from 1 January through 31 August 2016 with positive ZIKAV IgM results, and ZIKAV and DENV PRNTs were performed. PRNT result interpretations included ZIKAV, unspecified flavivirus, DENV infection, or negative. For this analysis, ZIKAV IgM was considered false positive for samples interpreted as a DENV infection or negative. In U.S. states, 208 (27%) of 759 IgM-positive results were confirmed to be ZIKAV compared to 11 (21%) of 52 in the U.S. Virgin Islands (USVI), 15 (15%) of 103 in American Samoa, and 13 (11%) of 123 in Puerto Rico. In American Samoa and Puerto Rico, more than 80% of IgM-positive results were unspecified flavivirus infections. The false-positivity rate was 27% in U.S. states, 18% in the USVI, 2% in American Samoa, and 6% in Puerto Rico. In U.S. states, the PRNT provided a virus-specific diagnosis or ruled out infection in the majority of IgM-positive samples. Almost a third of ZIKAV IgM-positive results were not confirmed; therefore, providers and patients must understand that IgM results are preliminary. In territories with historically higher rates of DENV transmission, the PRNT usually could not differentiate between ZIKAV and DENV infections.

OBJECTIVE:To describe the epidemiologic and clinical syndromes associated with pediatric neuroinvasive arboviral infections among children in the United States from 2003 through 2012.METHODS:We reviewed data reported by state health departments to ArboNET, the national arboviral surveillance system, for 2003 through 2012. Children (RESULTS:During the study period, 1217 cases and 22 deaths due to pediatric neuroinvasive arboviral infection were reported from the 48 contiguous states. La Crosse virus (665 cases; 55%) and West Nile virus (505 cases; 41%) were the most common etiologies identified. Although less common, Eastern equine encephalitis virus (30 cases; 2%) resulted in 10 pediatric deaths. La Crosse virus primarily affected younger children, whereas West Nile virus was more common in older children and adolescents. West Nile virus disease cases occurred throughout the country, whereas La Crosse and the other arboviruses were more focally distributed.CONCLUSIONS:Neuroinvasive arboviral infections were an important cause of pediatric disease from 2003 through 2012. Differences in the epidemiology and clinical disease result from complex interactions among virus, vector, host, and the environment. Decreasing the morbidity and mortality from these agents depends on vector control, personal protection to reduce mosquito and tick bites, and blood donor screening. Effective surveillance is critical to inform clinicians and public health officials about the epidemiologic features of these diseases and to direct prevention efforts.

Arthropod-borne viruses (arboviruses) are transmitted to humans primarily through the bites of infected mosquitoes and ticks. The leading cause of domestically acquired arboviral disease in the United States is West Nile virus (WNV) (1). Other arboviruses, including La Crosse, St. Louis encephalitis, Jamestown Canyon, Powassan, and eastern equine encephalitis viruses, also cause sporadic cases and outbreaks. This report summarizes surveillance data reported to CDC in 2015 for nationally notifiable arboviruses. It excludes dengue, chikungunya, and Zika viruses, which are primarily nondomestic viruses typically acquired through travel (and are addressed in other CDC reports). In 2015, 45 states and the District of Columbia (DC) reported 2,282 cases of domestic arboviral disease. Among these cases, 2,175 (95%) were WNV disease and 1,455 (67%) of those were classified as neuroinvasive disease (meningitis, encephalitis, or acute flaccid paralysis). The national incidence of WNV neuroinvasive disease was 0.45 cases per 100,000 population. Because arboviral diseases continue to cause serious illness, maintaining surveillance is important to direct prevention activities such as reduction of vector populations and screening of blood donors.

Zika virus is a mosquito-borne flavivirus primarily transmitted to humans by Aedes aegypti mosquitoes (1). Zika virus infections have also been documented through intrauterine transmission resulting in congenital infection; intrapartum transmission from a viremic mother to her newborn; sexual transmission; blood transfusion; and laboratory exposure (1-5). Most Zika virus infections are asymptomatic (1,6). Clinical illness, when it occurs, is generally mild and characterized by acute onset of fever, maculopapular rash, arthralgia, or nonpurulent conjunctivitis. However, Zika virus infection during pregnancy can cause adverse outcomes such as fetal loss, and microcephaly and other serious brain anomalies (1-3). Guillain-Barre syndrome, a rare autoimmune condition affecting the peripheral nervous system, also has been associated with Zika virus infection (1). Following the identification of local transmission of Zika virus in Brazil in May 2015, the virus has continued to spread throughout the Region of the Americas, and travel-associated cases have increased (7). In 2016, Zika virus disease and congenital infections became nationally notifiable conditions in the United States (8). As of September 3, 2016, a total of 2,382 confirmed and probable cases of Zika virus disease with symptom onset during January 1-July 31, 2016, had been reported from 48 of 50 U.S. states and the District of Columbia. Most cases (2,354; 99%) were travel-associated, with either direct travel or an epidemiologic link to a traveler to a Zika virus-affected area. Twenty-eight (1%) cases were reported as locally acquired, including 26 associated with mosquito-borne transmission, one acquired in a laboratory, and one with an unknown mode of transmission. Zika virus disease should be considered in patients with compatible clinical signs or symptoms who traveled to or reside in areas with ongoing Zika virus transmission or who had unprotected sex with someone who traveled to those areas. Health care providers should continue to educate patients, especially pregnant women, about the importance of avoiding infection with Zika virus, and all pregnant women should be assessed for possible Zika virus exposure at each prenatal visit (2).

SUMMARYAccurate data on the incidence of West Nile virus (WNV) disease are important for directing public health education and control activities. The objective of this project was to assess the underdiagnosis of WNV neuroinvasive disease through laboratory testing of patients with suspected viral meningitis or encephalitis at selected hospitals serving WNV-endemic regions in three states. Of the 279 patients with cerebrospinal fluid (CSF) specimens tested for WNV immunoglobulin M (IgM) antibodies, 258 (92%) were negative, 19 (7%) were positive, and two (1%) had equivocal results. Overall, 63% (12/19) of patients with WNV IgM-positive CSF had WNV IgM testing ordered by their attending physician. Seven (37%) cases would not have been identified as probable WNV infections without the further testing conducted through this project. These findings indicate that over a third of WNV infections in patients with clinically compatible neurological illness might be undiagnosed due to either lack of testing or inappropriate testing, leading to substantial underestimates of WNV neuroinvasive disease burden. Efforts should be made to educate healthcare providers and laboratorians about the local epidemiology of arboviral diseases and the optimal tests to be used in different clinical situations.

After reports of microcephaly and other adverse pregnancy outcomes in infants of mothers infected with Zika virus during pregnancy, CDC issued a travel alert on January 15, 2016, advising pregnant women to consider postponing travel to areas with active transmission of Zika virus. On January 19, CDC released interim guidelines for U.S. health care providers caring for pregnant women with travel to an affected area, and an update was released on February 5. As of February 17, CDC had received reports of nine pregnant travelers with laboratory-confirmed Zika virus disease; 10 additional reports of Zika virus disease among pregnant women are currently under investigation. No Zika virus-related hospitalizations or deaths among pregnant women were reported. Pregnancy outcomes among the nine confirmed cases included two early pregnancy losses, two elective terminations, and three live births (two apparently healthy infants and one infant with severe microcephaly); two pregnancies (approximately 18 weeks' and 34 weeks' gestation) are continuing without known complications. Confirmed cases of Zika virus infection were reported among women who had traveled to one or more of the following nine areas with ongoing local transmission of Zika virus: American Samoa, Brazil, El Salvador, Guatemala, Haiti, Honduras, Mexico, Puerto Rico, and Samoa. This report summarizes findings from the nine women with confirmed Zika virus infection during pregnancy, including case reports for four women with various clinical outcomes. U.S. health care providers caring for pregnant women with possible Zika virus exposure during pregnancy should follow CDC guidelines for patient evaluation and management. Zika virus disease is a nationally notifiable condition. CDC has developed a voluntary registry to collect information about U.S. pregnant women with confirmed Zika virus infection and their infants. Information about the registry is in preparation and will be available on the CDC website.

We conducted enhanced surveillance to identify medical risk factors for severe illness (i.e., hospitalization or death) and neuroinvasive disease (i.e., encephalitis or meningitis) among all West Nile virus disease cases reported from selected states from 2008 to 2010. Of the 1,090 case-patients included in the analysis, 708 (65%) case-patients were hospitalized, 641 (59%) case-patients had neuroinvasive disease, and 55 (5%) case-patients died. Chronic renal disease (adjusted odds ratio [aOR] = 4.1; 95% confidence interval [CI] = 1.4-12.1), history of cancer (aOR = 3.7; 95% CI = 1.8-7.5), history of alcohol abuse (aOR = 3.0; 95% CI = 1.3-6.7), diabetes (aOR = 2.2; 95% CI = 1.4-3.4), and hypertension (aOR = 1.5; 95% CI = 1.1-2.1) were independently associated with severe illness on multivariable analysis. Although the same medical conditions were independently associated with encephalitis, only hypertension was associated with meningitis. The only condition independently associated with death was immune suppression. Prevention messages should be targeted to persons with these conditions.

Objectives. We assessed the perceived utility of data collected through ArboNET, the national arboviral surveillance system, and evaluated state health department user satisfaction with system function. Methods. We used an online assessment tool to collect information about types of arboviral surveillance conducted, user satisfaction with ArboNET's performance, and use of data collected by the system. Representatives of all 53 reporting jurisdictions were asked to complete the assessment during spring 2009. Results. Representatives of 48 (91%) jurisdictions completed the assessment. Two-thirds of respondents were satisfied with ArboNET's overall performance. Most concerns were related to data transmission, particularly the lack of compatibility with the National Electronic Disease Surveillance System (NEDSS). Users found mosquito (85%), human disease (80%), viremic blood donor (79%), and veterinary disease (75%) surveillance data to be useful. While there was disagreement about the usefulness of avian mortality and sentinel animal surveillance, only 15% of users supported eliminating these categories. Respondents found weekly maps and tables posted on the U.S. Geological Survey (92%) and CDC (88%) websites to be the most useful reports generated from ArboNET data. Although many jurisdictions were willing to report additional clinical or laboratory data, time and resource constraints were considerations. Most respondents (71%) supported review and possible revision of the national case definition for human arboviral disease. Conclusions. As a result of this assessment, CDC and partner organizations have made ArboNET NEDSS-compatible and revised national case definitions for arboviral disease. Alternative data-sharing and reporting options are also being considered. Continued evaluation of ArboNET will help ensure that it continues to be a useful tool for national arboviral disease surveillance.

From 1999-2007, the most common causes of neuroinvasive arboviral disease in the United States, after West Nile virus (WNV), were California (CAL) serogroup viruses, St. Louis encephalitis virus (SLEV), and eastern equine encephalitis virus (EEEV). The CAL serogroup virus disease was primarily reported from Appalachia and the upper Midwest, SLEV disease from southern states, and EEEV disease from areas along the Atlantic and Gulf coasts. Children accounted for 88% of CAL serogroup virus disease, whereas 75% of SLEV disease occurred among older adults. The EEEV disease had the highest case-fatality rate (42%). The incidence of CAL serogroup virus and EEEV disease remained stable before and after the detection of WNV in the United States in 1999. The SLEV disease declined 3-fold after 1999; however, SLEV disease has occurred in sporadic epidemics that make trends difficult to interpret. The CAL serogroup virus, SLEV, and EEEV disease are persistent public health concerns in the United States warranting ongoing prevention efforts.

Yellow fever (YF) vaccine has been used for prevention of YF since 1937 with over 500 million doses administered. However, rare reports of severe adverse events following vaccination have raised concerns about the vaccine's safety. We reviewed reports of adverse events following YF vaccination reported to the U.S. Vaccine Adverse Event Reporting System (VAERS) from 2000 to 2006. We used estimates of age and sex distribution of administered doses obtained from a 2006 survey of authorized vaccine providers to calculate age- and sex-specific reporting rates of all serious adverse events (SAE), anaphylaxis, YF vaccine-associated neurotropic disease, and YF vaccine-associated viscerotropic disease. Reporting rates of SAEs were substantially higher in males and in persons aged > or =60 years. These findings reinforce the generally acceptable safety profile of YF vaccine, but highlight the importance of physician and traveler education regarding the risks and benefits of YF vaccination, particularly for travelers > or =60 years of age. Vaccination should be limited to persons traveling to areas where the risk of YF is expected to exceed the risk of serious adverse events after vaccination, or if not medically contraindicated, where national regulations require proof of vaccination to prevent introduction of YF.

Background : Yellow fever (YF) vaccines have been available since the 1930s and are generally considered safe and effective. However, rare reports of serious adverse events (SAE) following vaccination have prompted the Advisory Committee for Immunization Practices to periodically expand the list of conditions considered contraindications and precautions to vaccination. Methods : We describe adverse events following YF vaccination reported to the U.S. Vaccine Adverse Event Reporting System (VAERS) from 2007 through 2013 and calculate age- and sex-specific reporting rates of all SAE, anaphylaxis, YF vaccine-associated neurologic disease (YEL-AND) and YF vaccine-associated viscerotropic disease (YEL-AVD). Results : There were 938 adverse events following YF vaccination reported to VAERS from 2007 through 2013. Of these, 84 (9%) were classified as SAEs for a rate of 3.8 per 100 000 doses distributed. Reporting rates of SAEs increased with increasing age with a rate of 6.5 per 100 000 in persons aged 60–69 years and 10.3 for ≥70 years. The reporting rate for anaphylaxis was 1.3 per 100 000 doses distributed and was highest in persons ≤18 years (2.7 per 100 000). Reporting rates of YEL-AND and YEL-AVD were 0.8 and 0.3 per 100 000 doses distributed, respectively; both rates increased with increasing age. Conclusions : These findings reinforce the generally acceptable safety profile of YF vaccine, but highlight the importance of continued physician and traveller education regarding the risks and benefits of YF vaccination, particularly for older travellers.

Surveillance systems for West Nile virus (WNV) combine several methods to determine the location and timing of viral amplification. The value of each surveillance method must be measured against its efficiency and costs to optimize integrated vector management and suppress WNV transmission to the human population. Here we extend previous comparisons of WNV surveillance methods by equitably comparing the most common methods after standardization on the basis of spatial sampling density and costs, and by estimating optimal levels of sampling effort for mosquito traps and sentinel chicken flocks. In general, testing for evidence of viral RNA in mosquitoes and public-reported dead birds resulted in detection of WNV approximately 2–5 weeks earlier than serological monitoring of sentinel chickens at equal spatial sampling density. For a fixed cost, testing of dead birds reported by the public was found to be the most cost effective of the methods, yielding the highest number of positive results per $1000. Increased spatial density of mosquito trapping was associated with more precise estimates of WNV infection prevalence in mosquitoes. Our findings also suggested that the most common chicken flock size of 10 birds could be reduced to six to seven without substantial reductions in timeliness or sensitivity. We conclude that a surveillance system that uses the testing of dead birds reported by the public complemented by strategically timed mosquito and chicken sampling as agency resources allow would detect viral activity efficiently in terms of effort and costs, so long as susceptible bird species that experience a high mortality rate from infection with WNV, such as corvids, are present in the area.

Chikungunya virus is an emerging threat to the United States because humans are amplifying hosts and competent mosquito vectors are present in many regions of the country. We identified laboratory-confirmed chikungunya virus infections with diagnostic testing performed in the United States from 2010 through 2013. We described the epidemiology of these cases and determined which were reported to ArboNET. From 2010 through 2013, 115 laboratory-confirmed chikungunya virus infections were identified. Among 55 cases with known travel history, 53 (96%) reported travel to Asia and 2 (4%) to Africa. No locally-acquired infections were identified. Six patients had detectable viremia after returning to the United States. Only 21% of identified cases were reported to ArboNET, with a median of 72 days between illness onset and reporting. Given the risk of introduction into the United States, healthcare providers and public health officials should be educated about the recognition, diagnosis, and timely reporting of chikungunya virus disease cases.

West Nile virus (WNV) is an arthropod-borne virus (arbovirus) in the family Flaviviridae and is the leading cause of arboviral disease in the United States. An estimated 80% of WNV infections are asymptomatic. Most symptomatic persons develop an acute systemic febrile illness that often includes headache, myalgia, arthralgia, rash, or gastrointestinal symptoms. Less than 1% of infected persons develop neuroinvasive disease, which typically presents as encephalitis, meningitis, or acute flaccid paralysis.1999-2008.WNV disease is a nationally notifiable disease with standardized case definitions. State and metropolitan heath departments report cases to CDC through ArboNET, an electronic passive surveillance system. Variables collected include patient age, sex, race, county and state of residence, date of illness onset, clinical syndrome, and outcome of illness.During 1999-2008, a total of 28,961 confirmed and probable cases of WNV disease, including 11,822 (41%) WNV neuroinvasive disease cases, were reported to CDC from 47 states and the District of Columbia. No cases were reported from Alaska, Hawaii, Maine, or any U.S. territories. A total of 93% of all WNV patients had illness onset during July-September. The national incidence of WNV neuroinvasive disease peaked in 2002 (1.02 cases per 100,000 population) and was stable during 2004-2007 (mean annual incidence: 0.44; range: 0.39-0.50). In 2008, the incidence was 0.23 per 100,000 population, compared with 0.41 in 2007 and 0.50 in 2006. During 1999-2008, the highest incidence of neuroinvasive disease occurred in West North Central and Mountain states. Neuroinvasive disease incidence increased with increasing age, with the highest incidence (1.35 cases per 100,000 population) occurring among persons agedor=70 years. The hospitalization rate and case-fatality ratio increased with increasing age among persons with neuroinvasive disease.The stability in reported incidence of neuroinvasive disease during 2004-2007 might represent an endemic level of WNV transmission. Whether the incidence reported in 2008 represents a decrease that will continue is unknown; variations in vectors, avian amplifying hosts, human activity, and environmental factors make predicting future WNV transmission levels difficult.Surveillance of WNV disease is important for detecting and monitoring seasonal epidemics and targeting prevention and control activities. Public health education programs should focus on older persons, who are at increased risk for neurologic disease and poor clinical outcomes. In the absence of an effective human vaccine, WNV disease prevention depends on community-level mosquito control and household and personal protection measures.

From 1999-2007, the most common causes of neuroinvasive arboviral disease in the United States, after West Nile virus (WNV), were California (CAL) serogroup viruses, St. Louis encephalitis virus (SLEV), and eastern equine encephalitis virus (EEEV). The CAL serogroup virus disease was primarily reported from Appalachia and the upper Midwest, SLEV disease from southern states, and EEEV disease from areas along the Atlantic and Gulf coasts. Children accounted for 88% of CAL serogroup virus disease, whereas 75% of SLEV disease occurred among older adults. The EEEV disease had the highest case-fatality rate (42%). The incidence of CAL serogroup virus and EEEV disease remained stable before and after the detection of WNV in the United States in 1999. The SLEV disease declined 3-fold after 1999; however, SLEV disease has occurred in sporadic epidemics that make trends difficult to interpret. The CAL serogroup virus, SLEV, and EEEV disease are persistent public health concerns in the United States warranting ongoing prevention efforts.