Search

Problem/condition: Although chronic fatigue syndrome (CFS) has been recognized as a cause of morbidity in the United States, the etiology of CFS is unknown. In addition, information is incomplete concerning the clinical spectrum and prevalence of CFS in the United States., Reporting Period Covered: This report summarizes CFS surveillance data collected in four U.S. cities from September 1989 through August 1993., Description of System: A physician-based surveillance system for CFS was established in four U.S. metropolitan areas: Atlanta, Georgia; Wichita, Kansas; Grand Rapids, Michigan; and Reno, Nevada. The objectives of this surveillance system were to collect descriptive epidemiologic information from patients who had unexplained chronic fatigue, estimate the prevalence and incidence of CFS in defined populations, and describe the clinical course of CFS. Patients aged > or = 18 years who had had unexplained, debilitating fatigue or chronic unwellness for at least 6 months were referred by their physicians to a designated health professional(s) in their area. Those patients who participated in the surveillance system a) were interviewed by the health professional(s); b) completed a self-administered questionnaire that included their demographic information, medical history, and responses to the Beck Depression Inventory, the Diagnostic Interview Schedule, and the Sickness Impact Profile; c) submitted blood and urine samples for laboratory testing; and d) agreed to a review of their medical records. On the basis of this information, patients were assigned to one of four groups: those whose illnesses met the criteria of the 1988 CFS case definition (Group I); those whose fatigue or symptoms did not meet the criteria for CFS (Group II); those who had had an identifiable psychological disorder before onset of fatigue (Group III); and those who had evidence of other medical conditions that could have caused fatigue (Group IV). Patients assigned to Group III were further evaluated to determine the group to which they would have been assigned had psychological illness not been present, the epidemiologic characteristics of the illness and the frequency of symptoms among patients were evaluated, and the prevalence and incidence of CFS were estimated for each of the areas., Results: Of the 648 patients referred to the CFS surveillance system, 565 (87%) agreed to participate. Of these, 130 (23%) were assigned to Group I; 99 (18%), Group II; 235 (42%), Group III; and 101 (18%), Group IV. Of the 130 CFS patients, 125 (96%) were white and 111 (85%) were women. The mean age of CFS patients at the onset of illness was 30 years, and the mean duration of illness at the time of the interview was 6.7 years. Most (96%) CFS patients had completed high school, and 38% had graduated from college. The median annual household income/for CFS patients was $40,000. In the four cities, the age-, sex-, and race-adjusted prevalences of CFS for the 4-year surveillance period ranged from 4.0 to 8.7 per 100,000 population. The age-adjusted 4-year prevalences of CFS among white women ranged from 8.8 to 19.5 per 100,000 population., Interpretation: The results of this surveillance system were similar to those in previously published reports of CFS. Additional studies should be directed toward determining whether the data collected in this surveillance system were subject to selection bias (e.g., education and income levels might have influenced usage of the health-care system, and the populations of these four surveillance sites might not be representative of the U.S. population)., Actions Taken: In February 1997, CDC began a large-scale, cross-sectional study at one surveillance site (Wichita) to describe more completely the magnitude and epidemiology of unexplained chronic fatigue and CFS.

Problem/condition: CDC conducts active surveillance annually from October through May on the emergence and spread of influenza virus variants and the impact of influenza-related morbidity and mortality. Influenza activity is also monitored throughout the year by passive surveillance., Reporting Period Covered: This report summarizes U.S. influenza surveillance from October 1992 through May 1994., Description of System: Influenza surveillance comprises four components, three of which provide weekly data from October through May: a) state and territorial epidemiologists provide estimates of local influenza activity; b) approximately 140 sentinel physicians report their total number of patient visits and the number of cases of influenza-like illness; and c) approximately 70 collaborating laboratories of the World Health Organization (WHO) report weekly influenza virus isolations and submit selected influenza isolates to CDC for antigenic analysis. Throughout the year, vital statistics offices of 121 cities report deaths related to pneumonia and influenza (P&I), providing an index of the impact of influenza on mortality., Results: Influenza B viruses predominated during the 1992-93 influenza season, but influenza A(H3N2) isolates increased and were associated with outbreaks in nursing homes at the end of the season. The increase in influenza A(H3N2) activity was associated with a rise in P&I-related mortality. Preseason outbreaks of influenza A(H3N2) virus were reported during August and September 1993 in Louisiana. In the past, preseason outbreaks of influenza have been associated with earlier than usual epidemic-level activity. During the 1993-94 influenza season, activity rose during November and December and peaked earlier than usual, during the last week of December and the first week of January; influenza A(H3N2) viruses predominated., Interpretation: The change in predominance from influenza B to influenza A in the spring of 1993 emphasizes the importance of annual influenza surveillance. Although influenza vaccine is effective against both influenza A and B, the antiviral drugs amantadine and rimantadine are effective only against influenza A. Outbreaks during the summer of 1993 emphasize that influenza should be considered a possible cause of respiratory infections during summer and early autumn., Actions Taken: Surveillance data were provided weekly throughout the influenza season to public health officials, WHO, and health-care providers.

Problem/condition: CDC monitors the emergence and spread of new influenza virus variants and the impact of influenza on morbidity and mortality annually from October through May., Reporting Period Covered: This report covers United States influenza surveillance conducted from October 1988 through May 1989., Description of System: Weekly reports from the vital statistics offices of 121 cities provided an index of influenza's impact on mortality; 58 WHO collaborating laboratories reported weekly identification of influenza viruses; weekly morbidity reports were received both from the state and territorial epidemiologists and from 153 sentinel family practice physicians. Nonsystematic reports of outbreaks and unusual illnesses were received throughout the year., Results: During the 1988-89 influenza season, influenza A (H1N1) and B viruses were identified in the United States with essentially equal frequency overall, although both regional and temporal patterns of predominance shifted over the course of the season. Throughout the season increases in the indices of influenza morbidity in regions where influenza B predominated. Only 7% of identified viruses were influenza A (H3N2), but not isolations of this subtype increased as the season waned and it subsequently predominated during the 1989-90 season. During the 1988-89 season outbreaks in nursing homes were reported in association with influenza B and A (H3N2), but not influenza A (H1N1)., Interpretation: The alternating temporal and geographic predominance of influenza strains A (H1N1) and B during the 1988-89 season emphasizes the importance of continual attention to regional viral strain surveillance, since amantadine is effective only for treatment and prophylaxis of influenza A., Actions Taken: Weekly interim analyses of surveillance data produced throughout the season allow physicians and public health officials to make informed choices regarding appropriate use of amantadine. CDC's annual surveillance allows the observed viral variants to be assessed as candidates for inclusion as components in vaccines used in subsequent influenza seasons.

During the 1991-92 influenza season, sustained regional influenza activity began to be reported by state and territorial epidemiologists in the United States in mid-October 1991. Sustained reporting of widespread influenza activity began in early November 1991, 5-10 weeks earlier than in any of the previous nine influenza seasons. Influenza caused substantial morbidity among school-age children and excess mortality among the elderly. Regional outbreaks of influenza ended 2-6 weeks earlier than in the previous nine influenza seasons, based on the last sustained state and territorial epidemiologists' reports. Nationally, > 99% of isolates were influenza A. Influenza A(H3N2) predominated in all regions of the country, but isolation of influenza A(H1N1) increased proportionally as the season progressed. Isolation of influenza B (< 1% of total isolates) clustered after February. The majority of isolates characterized were antigenically similar to components in the 1991-92 influenza vaccine. However, an influenza A(H1N1) strain that had undergone antigenic drift was detected in many regions of the country; this strain will be included in the 1992-93 influenza vaccine.

During the 1989-90 influenza season, 98% of all influenza viruses isolated in the United States and reported to CDC were influenza A. Almost all those that were antigenically characterized were similar to influenza A/Shanghai/11/87(H3N2), a component of the 1989-90 influenza vaccine. Regional and widespread influenza activity began to be reported in late December 1989, peaked in mid-January 1990, and declined rapidly through early April 1990. Most of the outbreaks reported to CDC were among nursing-home residents. Considerable influenza-associated mortality was reflected in the percentage of deaths due to pneumonia and influenza (P&I) reported through the CDC 121 Cities Surveillance System from early January through early April. More than 80% of all reported P&I deaths were among persons greater than or equal to 65 years. In contrast to the predominance of influenza A during 1989-90, during the 1990-91 influenza season 86% of all influenza virus isolations reported were influenza B. Widespread influenza activity was reported from mid-January through April 1991, with regional activity extending into May. Outbreaks were reported primarily among schoolchildren, and no evidence of excess influenza-associated mortality was found. Almost all the influenza B isolates tested were related to influenza B/Yamagata/16/88, a component of the 1990-91 influenza vaccine, but were antigenically closer to B/Panama/45/90, a minor variant.