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Background Despite guidelines recommending narrow-spectrum perioperative antibiotics (NSPA) as prophylaxis for most children undergoing congenital heart disease (CHD) surgery, broad-spectrum perioperative antibiotics (BSPA) are variably used, and their impact on postoperative outcomes is poorly understood. Methods We used administrative data from U.S. hospitals participating in the Vizient Clinical Data Base. Admissions from 2011 to 2018 containing a qualifying CHD surgery in children 0–17 years old were evaluated for exposure to BSPA versus NSPA. Propensity score-adjusted models were used to compare postoperative length of hospital stay (PLOS) by exposure group, while adjusting for confounders. Secondary outcomes included subsequent antimicrobial treatment and in-hospital mortality. Results Among 18 088 eligible encounters from 24 U.S. hospitals, BSPA were given in 21.4% of CHD surgeries, with mean BSPA use varying from 1.7% to 96.1% between centers. PLOS was longer for BSPA-exposed cases (adjusted hazard ratio 0.79; 95% confidence interval [CI]: 0.71–0.89, P < .0001). BSPA was associated with higher adjusted odds of subsequent antimicrobial treatment (odds ratio [OR] 1.24; 95% CI: 1.06–1.48), and there was no significant difference in adjusted mortality between exposure groups (OR 2.06; 95% CI: 1.0–4.31; P = .05). Analyses of subgroups with the most BSPA exposure, including high-complexity procedures and delayed sternal closure, also did not find (but could not exclude) a measurable benefit from BSPA on PLOS. Conclusions BSPA use was common in high-risk populations, and varied substantially between centers. Standardizing perioperative antibiotic practices between centers may reduce unnecessary broad-spectrum antibiotic exposure and improve clinical outcomes.

Reducing avoidable antimicrobial exposure to pediatric patients with cancer is achievable and necessary to promote optimal short- and long-term outcomes. Multiple evidence-based practices are already well established but should be more consistently implemented. Important opportunities exist to further improve the evidence to guide selective antimicrobial use in pediatric oncology.

Background Diagnosis of invasive candidiasis (IC) relies on insensitive cultures; the relative utility of fungal biomarkers in children is unclear. Methods This multinational observational cohort study enrolled patients aged >120 days and Results Five hundred participants were enrolled at 22 centers in 3 countries, and IC was diagnosed in 13 (2.6%). Thirteen additional blood specimens were collected and successfully spiked with Candida species, to achieve a 5.0% event rate. Valid T2Candida, Fungitell, Platelia Candida Ag Plus, and Platelia Candida Ab Plus assay results were available for 438, 467, 473, and 473 specimens, respectively. Operating characteristics for T2Candida were most optimal for detecting IC due to any Candida species, with results as follows: sensitivity, 80.0% (95% confidence interval, 59.3%–93.2%), specificity 97.1% (95.0%–98.5%), positive predictive value, 62.5% (43.7%–78.9%), and negative predictive value, 98.8% (97.2%–99.6%). Only T2Candida and Platelia Candida Ag Plus assays met the threshold for combination testing. Positive result for either yielded the following results: sensitivity, 86.4% (95% confidence interval, 65.1%– 97.1%); specificity, 94.7% (92.0%–96.7%); positive predictive value, 47.5% (31.5%–63.9%); and negative predictive value, 99.2% (97.7%–99.8%). Conclusions T2Candida alone or in combination with Platelia Candida Ag Plus may be beneficial for rapid detection of Candida species in children with concern for IC. Clinical Trials Registration NCT02220790.

Background Although coronavirus disease 2019 (COVID-19) is a mild infection in most children, a small proportion develop severe or critical illness. Data describing agents with potential antiviral activity continue to expand such that updated guidance is needed regarding use of these agents in children. Methods A panel of pediatric infectious diseases physicians and pharmacists from 20 geographically diverse North American institutions was convened. Through a series of teleconferences and web-based surveys, a set of guidance statements was developed and refined based on review of the best available evidence and expert opinion. Results Given the typically mild course of COVID-19 in children, supportive care alone is suggested for most cases. For children with severe illness, defined as a supplemental oxygen requirement without need for noninvasive or invasive mechanical ventilation or extracorporeal membrane oxygenation (ECMO), remdesivir is suggested, preferably as part of a clinical trial if available. Remdesivir should also be considered for critically ill children requiring invasive or noninvasive mechanical ventilation or ECMO. A duration of 5 days is appropriate for most patients. The panel recommends against the use of hydroxychloroquine or lopinavir-ritonavir (or other protease inhibitors) for COVID-19 in children. Conclusions Antiviral therapy for COVID-19 is not necessary for the great majority of pediatric patients. For children with severe or critical disease, this guidance offers an approach for decision-making regarding use of remdesivir.

BackgroundAlthough coronavirus disease 2019 (COVID-19) is mild in nearly all children, a small proportion of pediatric patients develop severe or critical illness. Guidance is therefore needed regarding use of agents with potential activity against severe acute respiratory syndrome coronavirus 2 in pediatrics.MethodsA panel of pediatric infectious diseases physicians and pharmacists from 18 geographically diverse North American institutions was convened. Through a series of teleconferences and web-based surveys, a set of guidance statements was developed and refined based on review of best available evidence and expert opinion.ResultsGiven the typically mild course of pediatric COVID-19, supportive care alone is suggested for the overwhelming majority of cases. The panel suggests a decision-making framework for antiviral therapy that weighs risks and benefits based on disease severity as indicated by respiratory support needs, with consideration on a case-by-case basis of potential pediatric risk factors for disease progression. If an antiviral is used, the panel suggests remdesivir as the preferred agent. Hydroxychloroquine could be considered for patients who are not candidates for remdesivir or when remdesivir is not available. Antivirals should preferably be used as part of a clinical trial if available.ConclusionsAntiviral therapy for COVID-19 is not necessary for the great majority of pediatric patients. For those rare cases of severe or critical disease, this guidance offers an approach for decision-making regarding antivirals, informed by available data. As evidence continues to evolve rapidly, the need for updates to the guidance is anticipated.

Background Starting in November 2020, the US Food and Drug Administration (FDA) has issued Emergency Use Authorizations (EUAs) for multiple novel virus-neutralizing monoclonal antibody therapies, including bamlanivimab monotherapy (now revoked), bamlanivimab and etesivimab, casirivimab and imdevimab (REGEN-COV), and sotrovimab, for treatment or postexposure prophylaxis of Coronavirus disease 2019 (COVID-19) in adolescents (≥12 years of age) and adults with certain high-risk conditions. Previous guidance is now updated based on new evidence and clinical experience. Methods A panel of experts in pediatric infectious diseases, pediatric infectious diseases pharmacotherapy, and pediatric critical care medicine from 18 geographically diverse US institutions was convened. Through a series of teleconferences and web-based surveys, a guidance statement was developed and refined based on a review of the best available evidence and expert opinion. Results The course of COVID-19 in children and adolescents is typically mild, though more severe disease is occasionally observed. Evidence supporting risk stratification is incomplete. Randomized controlled trials have demonstrated the benefit of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2)-specific monoclonal antibody therapies in adults, but data on safety and efficacy in children or adolescents are limited. Potential harms associated with infusion reactions or anaphylaxis are reportedly low in adults. Conclusions Based on evidence available as of August 31, 2021, the panel suggests a risk-based approach to administration of SARS-CoV-2 monoclonal antibody therapy. Therapy is suggested for the treatment of mild to moderate COVID-19 in adolescents (≥12 years of age) at the highest risk of progression to hospitalization or severe disease. Therapeutic decision-making about those at moderate risk of severe disease should be individualized. Use as postexposure prophylaxis could be considered for those at the highest risk who have a high-risk exposure but are not yet diagnosed with COVID-19. Clinicians and health systems should ensure safe and timely implementation of these therapeutics that does not exacerbate existing healthcare disparities.

Background Invasive candidiasis is the most common invasive fungal disease in children and adolescents, but there are limited pediatric-specific antifungal effectiveness data. We compared the effectiveness of echinocandins to triazoles or amphotericin B formulations (triazole/amphotericin B) as initial directed therapy for invasive candidiasis. Methods This multinational observational cohort study enrolled patients aged >120 days and Results Seven-hundred and fifty invasive candidiasis episodes were identified. After exclusions, 541 participants (235 in the echinocandin group and 306 in the triazole/amphotericin B group) remained. Crude failure rates at 14 days for echinocandin and triazole/amphotericin B groups were 9.8% (95% confidence intervals [CI]: 6.0% to 13.6%) and 13.1% (95% CI: 9.3% to 16.8%), respectively. The adjusted 14-day risk difference between echinocandin and triazole/amphotericin B groups was −7.1% points (95% CI: −13.1% to −2.4%), favoring echinocandins. The risk difference was −0.4% (95% CI: −7.5% to 6.7%) at 30 days. Conclusions In children with invasive candidiasis, initial directed therapy with an echinocandin was associated with reduced failure rate at 14 days but not 30 days. These results may support echinocandins as initial directed therapy for invasive candidiasis in children and adolescents. Clinical Trials Registration NCT01869829.

Although invasive aspergillosis is the most common invasive mold infection, mucormycosis and other non-Aspergillus opportunistic mold infections are increasingly associated with significant morbidity and mortality among highly immunocompromised patients. Early clinical suspicion is critically important to accurately distinguish, diagnose, and appropriately treat these rapidly progressive infections. Their relative rarity compared with other infections in these patient populations makes diagnosis and treatment challenging owing to the lack of large-scale available data, and therefore, current clinical outcomes remain far from ideal.

The coronavirus disease 2019 (COVID-19) pandemic has created many challenges for pediatric solid organ transplant (SOT) recipients and their families. As the pandemic persists, patients and their families struggle to identify the best and safest practices for resuming activities as areas reopen. Notably, decisions about returning to school remain difficult. We assembled a team of pediatric infectious diseases (ID), transplant ID, public health, transplant psychology, and infection prevention and control specialists to address the primary concerns about school reentry for pediatric SOT recipients in the United States. Based on available literature and guidance from national organizations, we generated consensus statements pertaining to school reentry specific to pediatric SOT recipients. Although data are limited and the COVID-19 pandemic is highly dynamic, our goal was to create a framework from which providers and caregivers can identify the most important considerations for each pediatric SOT recipient to promote a safe return to school.

Antimicrobial use (AU) in days of therapy per 1000 patient-days (DOT/1000 pd) varies widely among children’s hospitals. We evaluated indirect standardization to adjust AU for case mix, a source of variation inadequately addressed by current measurements. Hospitalizations from the Pediatric Health Information System were grouped into 85 clinical strata. Observed to expected (O:E) ratios were calculated by indirect standardization and compared with DOT/1000 pd. Outliers were defined by O:E z-scores. Antibacterial DOT/1000 pd ranged from 345 to 776 (2.2-fold variation; interquartile range [IQR] 552–679), whereas O:E ratios ranged from 0.8 to 1.14 (1.4-fold variation; IQR 0.93–1.05). O:E ratios were moderately correlated with DOT/1000 pd (correlation estimate 0.44; 95% confidence interval, 0.19–0.64; P = .0009). Using indirect standardization to adjust for case mix reduces apparent AU variation and may enhance stewardship efforts by providing adjusted comparisons to inform interventions.

Author(s): Cordoro, Kelly M; Reynolds, Sean D; Wattier, Rachel; McCalmont, Timothy H | Abstract: Background/objectivesA recent marked increase in pediatric and adult patients presenting with purpuric acral lesions concerning for ischemia, thrombosis and necrosis has been observed in COVID-19 prevalent regions worldwide. The clinical and histopathological features and relationship to COVID-19 have not been well described. The objective of this case series is to describe the clinical features and determine the histopathologic findings and clinical implications of the clusters of acral perniosis cases identified in pediatric patients.MethodsWe describe six otherwise healthy adolescents-three siblings per family from two unrelated families-presented within a 48-hour period in April, 2020, with acral perniosis-like lesions in the context of over 30 similar patients who were evaluated within the same week.ResultsAffected patients had mild symptoms of viral upper respiratory infection (URI) or contact with symptomatic persons 1-2 weeks preceding the rash. They all presented with red to violaceous macules and dusky, purpuric plaques scattered on the mid and distal aspects of the toes. Skin biopsies performed on each of the six patients demonstrated near identical histopathologic findings to those of idiopathic perniosis, with a lymphocytic inflammatory infiltrate without evidence of thromboembolism or immune complex vasculitis. While SARS-CoV-2 polymerase chain reaction was negative, testing was performed 1-2 weeks after URI symptoms or sick contact exposure.ConclusionWe offer a clinical approach to evaluation of patients with this presentation and discuss the possibility that these skin findings represent a convalescent-phase cutaneous reaction to SARS-CoV-2 infection.

BACKGROUND Pediatric oncology patients are at an increased risk of invasive bacterial infection due to immunosuppression. The risk of such infection in the absence of severe neutropenia (absolute neutrophil count ≥ 500/μL) is not well established and a validated prediction model for blood stream infection (BSI) risk offers clinical usefulness. METHODS A 6-site retrospective external validation was conducted using a previously published risk prediction model for BSI in febrile pediatric oncology patients without severe neutropenia: the Esbenshade/Vanderbilt (EsVan) model. A reduced model (EsVan2) excluding 2 less clinically reliable variables also was created using the initial EsVan model derivative cohort, and was validated using all 5 external validation cohorts. One data set was used only in sensitivity analyses due to missing some variables. RESULTS From the 5 primary data sets, there were a total of 1197 febrile episodes and 76 episodes of bacteremia. The overall C statistic for predicting bacteremia was 0.695, with a calibration slope of 0.50 for the original model and a calibration slope of 1.0 when recalibration was applied to the model. The model performed better in predicting high-risk bacteremia (gram-negative or Staphylococcus aureus infection) versus BSI alone, with a C statistic of 0.801 and a calibration slope of 0.65. The EsVan2 model outperformed the EsVan model across data sets with a C statistic of 0.733 for predicting BSI and a C statistic of 0.841 for high-risk BSI. CONCLUSIONS The results of this external validation demonstrated that the EsVan and EsVan2 models are able to predict BSI across multiple performance sites and, once validated and implemented prospectively, could assist in decision making in clinical practice. Cancer 2017. © 2017 American Cancer Society.

Background Perioperative antibiotics (PA) are routinely given to children undergoing congenital heart disease (CHD) surgery to prevent surgical site infection. National guidelines recommend narrow-spectrum PA (such as Cefazolin) for most CHD procedures. However, indications for broad-spectrum PA are not well established, and limited literature suggests high exposure to broad-spectrum PA in this population. We performed a contemporary, multicenter description of prevalence and variability of broad-spectrum PA exposure within the pediatric CHD surgical population. Methods We identified children 0-17 years admitted to U.S. academically-affiliated centers participating in the Vizient Clinical Database/Resource Manager from 2011-2018. Patients who had ICD-9 and ICD-10 codes indicating a CHD surgical procedure with intravenous antibiotics initiated the day of surgery were eligible for inclusion. Antibiotics broader than first- and second-generation cephalosporins were designated broad-spectrum. We excluded centers with 5 or fewer annual procedures. We excluded patients undergoing heart transplant, concurrent non-cardiac procedures, and those with missing medication data. Results 19,152 hospital admissions from 24 centers met inclusion criteria. 55% of patients were male, 18% were under 30 days of age at time of surgery, and 5.1% had diagnosis codes for prematurity. Broad spectrum antibiotics were administered in 21.4% of CHD procedures during the study period. Between the 24 centers, the proportion of surgical cases given broad-spectrum PA ranged from 1.5% to 95%, which was unrelated to center annual surgical volume. Children under 30 days of age and those with prematurity were significantly more likely to receive broad-spectrum agents. Vancomycin was the primary antibiotic contributing to broad-spectrum PA exposure. Conclusion Substantial variation in broad-spectrum PA use was observed among children undergoing congenital heart disease surgery in academically affiliated United States centers from 2011-2018. Neonates and premature infants have the highest rates of exposure to broad-spectrum antibiotics. Standardization of perioperative antibiotics in CHD surgery is a potential intervention to limit antibiotic exposure in young infants. Disclosures All Authors: No reported disclosures

BackgroundDespite increasing neonatal antibiotic stewardship efforts, understanding of interhospital variation in neonatal antibiotic use is limited.MethodsA retrospective cohort study was conducted among primarily academically affiliated hospitals participating in the Vizient Clinical Database/Resource Manager. Neonatal discharges were identified by admission age ResultsThe 118 included hospitals represented 184 716 neonatal discharges; 22 hospitals with low NCC, 56 with medium NCC, and 40 with high NCC. Mean antibiotic DOT/1000 pd was 363 (standard deviation [SD], 94) in high NCC hospitals, 243 (SD, 88) in medium NCC hospitals, and 184 (SD, 122) in low NCC hospitals. Increasing NCC was associated with higher antibiotic use, with an incidence rate ratio (IRR) of 1.95 (95% confidence interval [CI], 1.55 to 2.47) for high vs low NCC and IRR 1.31 (95% CI, 1.05 to 1.64) for medium vs low NCC. Increasing case mix index was associated with higher antibiotic use (IRR 1.86 per unit increase; 95% CI, 1.50 to 2.31).ConclusionsAggregate antibiotic use among hospitalized neonates varies based on care complexity. Substantial variation despite stratification by complexity suggests incomplete risk adjustment and/or avoidable variation in care.

Fever and neutropenia (FN) is one of the most common, life-threatening, and costly complications of treatment for childhood cancer [1–3]. Although initial blood cultures identify bloodstream infections (BSI) in 10–20% of children with FN, the majority of episodes do not have an identified infectious etiology, and fever persists despite antibiotic therapy in up to 40% of cases [4–7]. Although blood cultures are frequently repeated in children with persistent FN, it is unclear how often this strategy identifies additional BSI, and how management is altered based on subsequent blood cultures. Potential harms of excessive blood culture collection include iatrogenic blood loss, which may increase transfusion requirements, and false positive results, which lead to additional laboratory testing, unnecessary antibiotic therapy, and increased costs [8–10]. The optimal approach to repeating blood cultures during persistent FN was identified as an important research gap in recent pediatric FN guidelines [11]. Prior studies examining the yield of subsequent blood cultures in patients with FN have demonstrated varying rates of new BSI. In an adult hematopoietic stem cell transplant (HSCT) cohort, 1 (0.9%) of 109 patients who had blood cultures collected after day 1 of FN had a new pathogen identified by follow-up culture [12]. In a study of children with FN whose initial cultures were negative, new BSI were identified via subsequent cultures in 24 (10%) of 220 episodes [13]. Because secondary infections may occur during treatment for the initial infection, it is also important to evaluate the yield of subsequent blood cultures in children whose initial cultures are positive [6, 14]. Subsequent blood culture yield should also be evaluated in pediatric HSCT recipients, a group with high incidence of persistent FN and high risk for BSI [4, 15]. At our center, blood cultures are repeated every 24 hours in the setting of ongoing FN. We evaluated the diagnostic yield of subsequent cultures in order to better characterize the utility of this approach in children with persistent FN, including those with previous positive cultures and HSCT recipients.

OBJECTIVETo evaluate interventions to reduce avoidable antibiotic use on pediatric oncology and hematopoietic stem cell transplantation (HSCT) services.DESIGNInterrupted time series.SETTINGAcademic pediatric hospital with separate oncology and HSCT services.PARTICIPANTSChildren admitted to the services during baseline (October 2011–August 2013) and 2 intervention periods, September 2013–June 2015 and July 2015–June 2016, including 1,525 oncology hospitalizations and 301 HSCT hospitalizations.INTERVENTIONIn phase 1, we completed an update of the institutional febrile neutropenia (FN) guideline for the pediatric oncology service, recommending first-line β-lactam monotherapy rather than routine use of 2 gram-negative agents. Phase 2 included updating the HSCT service FN guideline and engagement with a new pediatric antimicrobial stewardship program. The use of target antibiotics (tobramycin and ciprofloxacin) was measured in days of therapy per 1,000 patient days collected from administrative data. Intervention effects were evaluated using interrupted time series with segmented regression.RESULTSPhase 1 had mixed effects–long-term reduction in tobramycin use (97% below projected at 18 months) but rebound with increasing slope in ciprofloxacin use (+18% per month). Following phase 2, tobramycin and ciprofloxacin use on the oncology service were both 99% below projected levels at 12 months. On the HSCT service, tobramycin use was 99% below the projected level and ciprofloxacin use was 96% below the projected level at 12 months.CONCLUSIONSLocally adapted guidelines can facilitate practice changes in oncology and HSCT settings. More comprehensive and ongoing interventions, including follow-up education, feedback, and engagement of companion services may be needed to sustain changes.Infect Control Hosp Epidemiol2017;38:1039–1047

Background Antibiotics are often necessary in high-risk patients such as neonates. However, exposure to broad-spectrum antibiotics has been associated with adverse neonatal outcomes. Variation in antibiotic use across neonatal intensive care units has been demonstrated on a regional level, but little is known about United States nationwide antibiotic use among hospitalized neonates. Prior studies have measured antibiotic use rates (AUR; antibiotic therapy days as a portion of days present) rather than antibiotic days of therapy per 1,000 patient-days (DOT/1,000 patient-days), the preferred metric in antimicrobial stewardship practice. Methods Hospitals participating in the Vizient (formerly University HealthSystem Consortium) Clinical Database/Resource Manager with >100 neonatal discharges from January to December 2016 were identified. Facility-level clinical outcomes, diagnoses, and antibiotic utilization data from 118 hospitals were included. The primary antibiotic utilization metric was DOT per 1,000 patient-days; AUR and antibiotic spectrum index (ASI) per antibiotic day were also evaluated according to previously published methods. Results The number of neonatal discharges per facility in 2016 ranged from 228 to 15,773 (median 2,578, interquartile range [IQR] 1,314–3,927). Of the 118 hospitals, 94 (80%) provided care to neonates with birthweight less than 1,500 g, 77 (65%) performed major surgical procedures, 32 (27%) performed cardiac surgery, and 19 (16%) performed extracorporeal membrane oxygenation. Across all hospitals, there was 71-fold variation in antibiotic DOT/1,000 patient-days with range from 7.9 to 560.7 (median 271.1; IQR 181.7–347.5) and 85-fold variation in AUR with range from 0.4% to 34.1% of days present (median 16.7%; IQR 10.7%–20.8%). The ASI per antibiotic day ranged from 2.0 to 7.4 (median 6.2; IQR 5.8–6.5). Conclusion There is substantial variation in antibiotic use among neonates hospitalized in academically affiliated United States centers. Variation in days of exposure is greater than variation in spectrum of activity per day of therapy. Understanding sources of variation in antibiotic use at the facility level will be important to provide informative benchmarking of neonatal antimicrobial management. Disclosures All authors: No reported disclosures.

Background Invasive mold infections (IMIs) are a leading cause of mortality in immunocompromised children, yet there has never been an international epidemiologic investigation of pediatric IMIs. Methods This international, prospective cohort study was performed to characterize the epidemiology, antifungal therapy, and outcomes of pediatric IMIs. Children (≤18 years) with proven or probable IMIs were enrolled between August 2007 and May 2011 at 22 sites. Risk factors, underlying diagnoses, and treatments were recorded. Outcomes were assessed at 12 weeks after diagnosis using European Organization for Research and Treatment of Cancer/Mycoses Study Group response criteria. Results One hundred thirty-one pediatric patients with IMIs were enrolled; the most common IMI was invasive aspergillosis ([IA] 75%). Children with IA and those with other types of IMIs had similar underlying risk factors, except that children with IMIs caused by non-Aspergillus species were more likely to have received mold-active antifungal agents preceding diagnosis. The most commonly used antifungal classes after diagnosis were triazoles (82%) and polyenes (63%). Combination therapy was used in 53% of patients. Use of combination therapy was associated with an increased risk of adverse events (risk ratio, 1.98; 95% confidence interval, 1.06-3.68; P = .031), although there was no detectable difference in outcome. Conclusions Although risk factors for IMIs are similar across specific subtypes, preceding antifungal therapy may be an important modifier. Combination antifungal therapy requires further study to determine its true risks and benefits.

Borrelia burgdorferi produces Pfs and LuxS enzymes for breakdown of the toxic byproducts of methylation reactions, producing 4,5-dihydroxy-2,3-pentanedione (DPD), adenine, and homocysteine. DPD and its spontaneously rearranged derivatives constitute a class of bacterial pheromones named autoinducer-2 (AI-2). We describe that B. burgdorferi produces DPD during laboratory cultivation. Furthermore, addition of in vitro synthesized DPD to cultured B. burgdorferi resulted in altered expression levels of a specific set of bacterial proteins, among which is the outer surface lipoprotein VlsE. While a large number of bacteria utilize homocysteine, the other LuxS product, for synthesis of methionine as part of the activated-methyl cycle, B. burgdorferi was found to lack that ability. We propose that the main function of B. burgdorferi LuxS is to synthesize DPD and that the Lyme disease spirochete utilizes a form of DPD as a pheromone to control gene expression.

Background Respiratory syncytial virus (RSV) is the major respiratory pathogen of infants and young children. During each seasonal epidemic, multiple strains of both subgroup A and B viruses circulate in the community. Like other RNA viruses, RSV genome replication is prone to errors that results in a heterogeneous population of viral strains some of which may possess differences in virulence. We sought to determine whether clinical isolates of RSV differ in their capacity to induce inflammatory cytokines IL-6 and CCL5 (previously known as RANTES [regulated upon activation, normal T-cell expressed and secreted protein]), which are known to be induced in vitro and in vivo in response to RSV, during infection of A549 cells. Results Screening of subgroup A and B isolates revealed heterogeneity among strains to induce IL-6 and CCL5. We chose two subgroup B strains, New Haven (NH)1067 and NH1125, for further analysis because of their marked differences in cytokine inducing properties and because subgroup B strains, in general, are less genetically heterogeneous as compared to subgroup A strains. At 12 and 24 hours post infection RSV strains, NH1067 and NH1125 differed in their capacity to induce IL-6 by an order of magnitude or more. The concentrations of IL-6 and CCL5 were dependent on the dose of infectious virus and the concentration of these cytokines induced by NH1125 was greater than that of those induced by NH1067 when the multiplicity of infection of NH1067 used was as much as 10-fold higher than that of NH1125. The induction of IL-6 was dependent on viable virus as infection with UV-inactivated virus did not induce IL-6. The difference in IL-6 induction most likely could not be explained by differences in viral replication kinetics. The intracellular level of RSV RNA, as determined by quantitative RT-PCR, was indistinguishable between the 2 strains though the titer of progeny virus produced by NH1125 was greater than that produced by NH1067 at 16, 24 and 36 hours but essentially equal at 48 and 72 hours. Full genome sequencing of the 2 strains revealed 193 polymorphisms and 4 insertions in NH1067when compared to NH1125 (2 single base insertions in non-coding regions and 2 duplications of 3 and 60 bases in the RSV G gene). Of the polymorphisms, 147 occurred in coding regions and only 30 resulted in amino acid changes in 7 of the RSV genes. Conclusions These data suggest that RSV strains may not be homogeneous with regard to pathogenesis or virulence. Identification of the genetic polymorphisms associated with variations in cytokine induction may lead to insights into RSV disease and to the development of effective antiviral agents and vaccines.

Defining the metabolic capabilities and regulatory mechanisms controlling gene expression is a valuable step in understanding the pathogenic properties of infectious agents such as Borrelia burgdorferi . The present studies demonstrated that B. burgdorferi encodes functional Pfs and LuxS enzymes for the breakdown of toxic products of methylation reactions. Consistent with those observations, B. burgdorferi was shown to synthesize the end product 4,5-dihydroxy-2,3-pentanedione (DPD) during laboratory cultivation. DPD undergoes spontaneous rearrangements to produce a class of pheromones collectively named autoinducer 2 (AI-2). Addition of in vitro-synthesized DPD to cultured B. burgdorferi resulted in differential expression of a distinct subset of proteins, including the outer surface lipoprotein VlsE. Although many bacteria can utilize the other LuxS product, homocysteine, for regeneration of methionine, B. burgdorferi was found to lack such ability. It is hypothesized that B. burgdorferi produces LuxS for the express purpose of synthesizing DPD and utilizes a form of that molecule as an AI-2 pheromone to control gene expression.

The Lyme disease spirochete, Borrelia burgdorferi, utilizes a LuxS/autoinducer-2-dependent quorum sensing mechanism to control a specific subset of bacterial proteins. It is hypothesized that this system facilitates transmission of B. burgdorferi from feeding ticks into warm-blooded hosts.