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Montgomery MP, Morris SE, Rolfes MA, Kittikraisak W, Samuels AM, Biggerstaff M, Davis WW, Reed C, Olsen SJ. The role of asymptomatic infections in influenza transmission: what do we really know. THE LANCET. INFECTIOUS DISEASES 2024; 24:e394-e404. [PMID: 38128563 PMCID: PMC11127787 DOI: 10.1016/s1473-3099(23)00619-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/31/2023] [Revised: 09/02/2023] [Accepted: 09/18/2023] [Indexed: 12/23/2023]
Abstract
Before the COVID-19 pandemic, the role of asymptomatic influenza virus infections in influenza transmission was uncertain. However, the importance of asymptomatic infection with SARS-CoV-2 for onward transmission of COVID-19 has led experts to question whether the role of asymptomatic influenza virus infections in transmission had been underappreciated. We discuss the existing evidence on the frequency of asymptomatic influenza virus infections, the extent to which they contribute to infection transmission, and remaining knowledge gaps. We propose priority areas for further evaluation, study designs, and case definitions to address existing knowledge gaps.
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Affiliation(s)
- Martha P Montgomery
- Influenza Division, National Center for Immunization and Respiratory Diseases, US Centers for Disease Control and Prevention, Atlanta, GA, USA; Thailand Ministry of Public Health-US Centers for Disease Control and Prevention Collaboration, Department of Disease Control, Ministry of Public Health, Nonthaburi, Thailand.
| | - Sinead E Morris
- Influenza Division, National Center for Immunization and Respiratory Diseases, US Centers for Disease Control and Prevention, Atlanta, GA, USA
| | - Melissa A Rolfes
- Influenza Division, National Center for Immunization and Respiratory Diseases, US Centers for Disease Control and Prevention, Atlanta, GA, USA
| | - Wanitchaya Kittikraisak
- Influenza Division, National Center for Immunization and Respiratory Diseases, US Centers for Disease Control and Prevention, Atlanta, GA, USA; Thailand Ministry of Public Health-US Centers for Disease Control and Prevention Collaboration, Department of Disease Control, Ministry of Public Health, Nonthaburi, Thailand
| | - Aaron M Samuels
- Influenza Division, National Center for Immunization and Respiratory Diseases, US Centers for Disease Control and Prevention, Atlanta, GA, USA
| | - Matthew Biggerstaff
- Influenza Division, National Center for Immunization and Respiratory Diseases, US Centers for Disease Control and Prevention, Atlanta, GA, USA
| | - William W Davis
- Influenza Division, National Center for Immunization and Respiratory Diseases, US Centers for Disease Control and Prevention, Atlanta, GA, USA; Thailand Ministry of Public Health-US Centers for Disease Control and Prevention Collaboration, Department of Disease Control, Ministry of Public Health, Nonthaburi, Thailand
| | - Carrie Reed
- Influenza Division, National Center for Immunization and Respiratory Diseases, US Centers for Disease Control and Prevention, Atlanta, GA, USA
| | - Sonja J Olsen
- Influenza Division, National Center for Immunization and Respiratory Diseases, US Centers for Disease Control and Prevention, Atlanta, GA, USA
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Best JH, Sadeghi M, Sun X, Seetasith A, Albensi L, Joshi S, Zervos MJ. Household Influenza Transmission and Healthcare Resource Utilization Among Patients Treated with Baloxavir vs Oseltamivir: A United States Outpatient Prospective Survey. Infect Dis Ther 2024; 13:685-697. [PMID: 38483775 PMCID: PMC11058184 DOI: 10.1007/s40121-024-00937-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2023] [Accepted: 02/02/2024] [Indexed: 04/30/2024] Open
Abstract
INTRODUCTION Influenza is a common, seasonal infectious disease with broad medical, economic, and social consequences. Real-world evidence on the effect of influenza treatment on household transmission and healthcare resource utilization is limited in outpatient settings in the USA. This study examined the real-world effectiveness of baloxavir vs oseltamivir in reducing influenza household transmission and healthcare resource utilization. METHODS This prospective electronic survey on patient-reported outcomes was conducted between October 2022 and May 2023 via CVS Pharmacy in the USA. Adult participants (≥ 18 years old) were eligible if they filled a prescription for baloxavir or oseltamivir at a CVS Pharmacy within 2 days of influenza symptom onset. Participant demographics, household transmission, and all-cause healthcare resource utilization were collected. Transmission and utilization outcomes were assessed using χ2 and Fisher exact tests. RESULTS Of 87,871 unique patients contacted, 1346 (1.5%) consented. Of 374 eligible patients, 286 (90 baloxavir- and 196 oseltamivir-treated patients) completed the survey and were included in the analysis. Mean age of participants was 45.4 years, 65.6% were female, and 86.7% were White. Lower household transmission was observed with baloxavir compared with oseltamivir therapy (17.8% vs 26.5%; relative risk = 0.67; 95% CI 0.41-1.11). Healthcare resource utilization, particularly emergency department visits (0.0% vs 4.6%), was also numerically lower in the baloxavir-treated group; no hospitalizations were reported in either cohort. CONCLUSIONS The findings from this real-world study suggest that antiviral treatment of influenza with baloxavir may decrease household transmission and reduce healthcare resource utilization compared with oseltamivir.
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Affiliation(s)
| | | | - Xiaowu Sun
- CVS Health Clinical Trial Services, New York, NY, USA
| | | | - Lisa Albensi
- CVS Health Clinical Trial Services, New York, NY, USA
| | - Seema Joshi
- Infectious Diseases, Henry Ford Health System, Henry Ford Hospital, 2799 West Grand Blvd, Detroit, MI, 48202, USA
| | - Marcus J Zervos
- Infectious Diseases, Henry Ford Health System, Henry Ford Hospital, 2799 West Grand Blvd, Detroit, MI, 48202, USA.
- College of Human Medicine, Michigan State University, East Lansing, MI, USA.
- Wayne State University School of Medicine, Detroit, MI, USA.
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Dahlgren FS, Foppa IM, Stockwell MS, Vargas CY, LaRussa P, Reed C. Household transmission of influenza A and B within a prospective cohort during the 2013-2014 and 2014-2015 seasons. Stat Med 2021; 40:6260-6276. [PMID: 34580901 PMCID: PMC9293304 DOI: 10.1002/sim.9181] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2021] [Revised: 07/22/2021] [Accepted: 08/15/2021] [Indexed: 01/01/2023]
Abstract
People living within the same household as someone ill with influenza are at increased risk of infection. Here, we use Markov chain Monte Carlo methods to partition the hazard of influenza illness within a cohort into the hazard from the community and the hazard from the household. During the 2013‐2014 influenza season, 49 (4.7%) of the 1044 people enrolled in a community surveillance cohort had an acute respiratory illness (ARI) attributable to influenza. During the 2014‐2015 influenza season, 50 (4.7%) of the 1063 people in the cohort had an ARI attributable to influenza. The secondary attack rate from a household member was 2.3% for influenza A (H1) during 2013‐2014, 5.3% for influenza B during 2013‐2014, and 7.6% for influenza A (H3) during 2014‐2015. Living in a household with a person ill with influenza increased the risk of an ARI attributable to influenza up to 350%, depending on the season and the influenza virus circulating within the household.
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Affiliation(s)
- F Scott Dahlgren
- Influenza Division, Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, USA
| | - Ivo M Foppa
- Influenza Division, Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, USA.,Battelle Memorial Institute, Atlanta, Georgia, USA
| | - Melissa S Stockwell
- Division of Child and Adolescent Health, Department of Pediatrics, College of Physicians and Surgeons, Columbia University, New York, New York, USA.,Department of Population and Family Health, Mailman School of Public Health, Columbia University, New York, New York, USA
| | - Celibell Y Vargas
- Division of Child and Adolescent Health, Department of Pediatrics, College of Physicians and Surgeons, Columbia University, New York, New York, USA
| | - Philip LaRussa
- Division of Pediatric Infectious Diseases, Department of Pediatrics, College of Physicians and Surgeons, Columbia University, New York, New York, USA
| | - Carrie Reed
- Influenza Division, Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, USA
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Biondo GF, Santana JC, Lago PM, Piva J, Souza PRA, Gaulke JG, Sebben JM. Impact of A/H1N1 influenza in children at a Brazilian University Hospital. Braz J Infect Dis 2018; 22:219-223. [PMID: 29879425 PMCID: PMC9425643 DOI: 10.1016/j.bjid.2018.05.004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2017] [Revised: 05/09/2018] [Accepted: 05/13/2018] [Indexed: 11/24/2022] Open
Abstract
BACKGROUND A/H1N1 influenza is a viral disease that affects a significant part of the population mainly in winter, leading to increased number of medical consultations, hospitalizations and consequently care spending in emergency. METHODS This is a case-series retrospective study, involving patients admitted to a tertiary hospital in southern Brazil in 2016 with a clinical diagnosis of acute respiratory infection of the influenza type and laboratory confirmation of influenza A/H1N1. RESULTS 64 patients were included, mostly male, median age of 48.3 months. Chronic underlying diseases were found in 73% of the patients, and these patients evolved to the most unfavorable outcome. About vaccination, of the 57 patients with an age range for vaccination, only 28% had complete vaccination coverage. The main clinical manifestations found in the included patients were fever, cough, intercostal indrawing, wheezing, tachypnea and pulmonary crackles. These patients were mainly followed-up with laboratory tests and chest X-ray. Consolidation was evident in 43% of patients followed by interstitial infiltrate in 33%. A five-day course of neuraminidase inhibitor was prescribed for all patients, as recommended by the WHO, but due to the complications, 73% of the patients required antibiotic therapy, and 61% oxygen therapy. The majority of patients had a favorable outcome, but 11 required intensive care and one died. CONCLUSIONS A/H1N1 influenza persists as an important public health problem, mainly due to high morbidity and hospitalization rates. It is important to identify patients with A/H1N1 influenza and clinical situations with higher risk of complications. Through this study, it is possible to analyze the characteristics of pediatric patients with A/H1N1 influenza and mainly to emphasize assistance of populations with comorbidities, since they present higher rates of complications and death.
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Affiliation(s)
- Gabriela Fontanella Biondo
- Hospital de Clínicas de Porto Alegre (HCPA), Emergência e Medicina Intensiva Pediátrica, Emergência Pediátrica, Porto Alegre, RS, Brazil
| | - João Carlos Santana
- Universidade Federal do Rio Grande do Sul (UFRGS), Departamento de Pediatria, Emergência e Medicina Intensiva Pediátrica (HCPA), Porto Alegre, RS, Brazil
| | - Patrícia M Lago
- Universidade Federal do Rio Grande do Sul (UFRGS), Departamento de Pediatria, Emergência e Medicina Intensiva Pediátrica (HCPA), Porto Alegre, RS, Brazil
| | - Jefferson Piva
- Universidade Federal do Rio Grande do Sul (UFRGS), Departamento de Pediatria, Emergência e Medicina Intensiva Pediátrica (HCPA), Porto Alegre, RS, Brazil
| | - Paulo Ricardo A Souza
- Universidade Federal do Rio Grande do Sul (UFRGS), Faculdade de Medicina, Porto Alegre, RS, Brazil
| | - Joana Genz Gaulke
- Universidade Federal do Rio Grande do Sul (UFRGS), Faculdade de Medicina, Porto Alegre, RS, Brazil
| | - Juliana M Sebben
- Hospital de Clínicas de Porto Alegre (HCPA), Residência em Pediatria, Porto Alegre, RS, Brazil
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Morozova O, Cohen T, Crawford FW. Risk ratios for contagious outcomes. J R Soc Interface 2018; 15:20170696. [PMID: 29343627 PMCID: PMC5805970 DOI: 10.1098/rsif.2017.0696] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2017] [Accepted: 12/18/2017] [Indexed: 12/12/2022] Open
Abstract
Epidemiologists commonly use the risk ratio to summarize the relationship between a binary covariate and outcome, even when outcomes may be dependent. Investigations of transmissible diseases in clusters-households, villages or small groups-often report risk ratios. Epidemiologists have warned that risk ratios may be misleading when outcomes are contagious, but the nature of this error is poorly understood. In this study, we assess the meaning of the risk ratio when outcomes are contagious. We provide a mathematical definition of infectious disease transmission within clusters, based on the canonical stochastic susceptible-infective model. From this characterization, we define the individual-level ratio of instantaneous infection risks as the inferential target, and evaluate the properties of the risk ratio as an approximation of this quantity. We exhibit analytically and by simulation the circumstances under which the risk ratio implies an effect whose direction is opposite that of the true effect of the covariate. In particular, the risk ratio can be greater than one even when the covariate reduces both individual-level susceptibility to infection, and transmissibility once infected. We explain these findings in the epidemiologic language of confounding and Simpson's paradox, underscoring the pitfalls of failing to account for transmission when outcomes are contagious.
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Affiliation(s)
- Olga Morozova
- Department of Epidemiology of Microbial Diseases, Yale School of Public Health, 60 College Street, New Haven, CT 06510, USA
| | - Ted Cohen
- Department of Epidemiology of Microbial Diseases, Yale School of Public Health, 60 College Street, New Haven, CT 06510, USA
| | - Forrest W Crawford
- Department of Biostatistics, Yale School of Public Health, 60 College Street, New Haven, CT 06510, USA
- Department of Ecology and Evolutionary Biology, Yale University, 165 Prospect St, New Haven, CT 06511, USA
- Yale School of Management, 165 Whitney Ave, New Haven, CT 06511, USA
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Review Article: The Fraction of Influenza Virus Infections That Are Asymptomatic: A Systematic Review and Meta-analysis. Epidemiology 2016; 26:862-72. [PMID: 26133025 DOI: 10.1097/ede.0000000000000340] [Citation(s) in RCA: 99] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
BACKGROUND The fraction of persons with influenza virus infection, who do not report any signs or symptoms throughout the course of infection is referred to as the asymptomatic fraction. METHODS We conducted a systematic review and meta-analysis of published estimates of the asymptomatic fraction of influenza virus infections. We found that estimates of the asymptomatic fraction were reported from two different types of studies: first, outbreak investigations with short-term follow-up of potentially exposed persons and virologic confirmation of infections; second, studies conducted across epidemics typically evaluating rates of acute respiratory illness among persons with serologic evidence of infection, in some cases adjusting for background rates of illness from other causes. RESULTS Most point estimates from studies of outbreak investigations fell in the range 4%-28% with low heterogeneity (I = 0%) with a pooled mean of 16% (95% confidence interval = 13%, 19%). Estimates from the studies conducted across epidemics without adjustment were very heterogeneous (point estimates 0%-100%; I = 97%), while estimates from studies that adjusted for background illnesses were more consistent with point estimates in the range 65%-85% and moderate heterogeneity (I = 58%). Variation in estimates could be partially explained by differences in study design and analysis, and inclusion of mild symptomatic illnesses as asymptomatic in some studies. CONCLUSIONS Estimates of the asymptomatic fraction are affected by the study design, and the definitions of infection and symptomatic illness. Considerable differences between the asymptomatic fraction of infections confirmed by virologic versus serologic testing may indicate fundamental differences in the interpretation of these two indicators.
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Vargas CY, Wang L, Castellanos de Belliard Y, Morban M, Diaz H, Larson EL, LaRussa P, Saiman L, Stockwell MS. Pilot study of participant-collected nasal swabs for acute respiratory infections in a low-income, urban population. Clin Epidemiol 2016; 8:1-5. [PMID: 26793005 PMCID: PMC4708198 DOI: 10.2147/clep.s95847] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Objective To assess the feasibility and validity of unsupervised participant-collected nasal swabs to detect respiratory pathogens in a low-income, urban minority population. Methods This project was conducted as part of an ongoing community-based surveillance study in New York City to identify viral etiologies of acute respiratory infection. In January 2014, following sample collection by trained research assistants, participants with acute respiratory infection from 30 households subsequently collected and returned a self-collected/parent-collected nasal swab via mail. Self/parental swabs corresponding with positive reverse transcription polymerase chain reaction primary research samples were analyzed. Results Nearly all (96.8%, n=30/31) households agreed to participate; 100% reported returning the sample and 29 were received (median time: 8 days). Most (18; 62.1%) of the primary research samples were positive. For eight influenza-positive research samples, seven (87.5%) self-swabs were also positive. For ten other respiratory pathogen-positive research samples, eight (80.0%) self-swabs were positive. Sensitivity of self-swabs for any respiratory pathogen was 83.3% and 87.5% for influenza, and specificity for both was 100%. There was no relationship between level of education and concordance of results between positive research samples and their matching participant swab. Conclusion In this pilot study, self-swabbing was feasible and valid in a low-income, urban minority population.
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Affiliation(s)
| | - Liqun Wang
- Department of Pediatrics, Columbia University, New York, NY, USA
| | | | - Maria Morban
- Department of Pediatrics, Columbia University, New York, NY, USA
| | - Hilbania Diaz
- Department of Pediatrics, Columbia University, New York, NY, USA
| | - Elaine L Larson
- School of Nursing, Columbia University, New York, NY, USA; Department of Epidemiology, Mailman School of Public Health, Columbia University, New York, NY, USA
| | - Philip LaRussa
- Department of Pediatrics, Columbia University, New York, NY, USA
| | - Lisa Saiman
- Department of Pediatrics, Columbia University, New York, NY, USA; Department of Infection Prevention and Control, NewYork-Presbyterian Hospital, Columbia University, New York, NY, USA
| | - Melissa S Stockwell
- Department of Pediatrics, Columbia University, New York, NY, USA; Department of Population and Family Health, Mailman School of Public Health, Columbia University, New York, NY, USA; NewYork-Presbyterian Hospital, New York, NY, USA
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Transmission of the First Influenza A(H1N1)pdm09 Pandemic Wave in Australia Was Driven by Undetected Infections: Pandemic Response Implications. PLoS One 2015; 10:e0144331. [PMID: 26692335 PMCID: PMC4687009 DOI: 10.1371/journal.pone.0144331] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2015] [Accepted: 10/15/2015] [Indexed: 02/03/2023] Open
Abstract
Background During the first wave of influenza A(H1N1)pdm09 in Victoria, Australia the rapid increase in notified cases and the high proportion with relatively mild symptoms suggested that community transmission was established before cases were identified. This lead to the hypothesis that those with low-level infections were the main drivers of the pandemic. Methods A deterministic susceptible-infected-recovered model was constructed to describe the first pandemic wave in a population structured by disease severity levels of asymptomatic, low-level symptoms, moderate symptoms and severe symptoms requiring hospitalisation. The model incorporated mixing, infectivity and duration of infectiousness parameters to calculate subgroup-specific reproduction numbers for each severity level. Results With stratum-specific effective reproduction numbers of 1.82 and 1.32 respectively, those with low-level symptoms, and those with asymptomatic infections were responsible for most of the transmission. The effective reproduction numbers for infections resulting in moderate symptoms and hospitalisation were less than one. Sensitivity analyses confirmed the importance of parameters relating to asymptomatic individuals and those with low-level symptoms. Conclusions Transmission of influenza A(H1N1)pdm09 was largely driven by those invisible to the health system. This has implications for control measures–such as distribution of antivirals to cases and contacts and quarantine/isolation–that rely on detection of infected cases. Pandemic plans need to incorporate milder scenarios, with a graded approach to implementation of control measures.
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Tsang TK, Lau LLH, Cauchemez S, Cowling BJ. Household Transmission of Influenza Virus. Trends Microbiol 2015; 24:123-133. [PMID: 26612500 PMCID: PMC4733423 DOI: 10.1016/j.tim.2015.10.012] [Citation(s) in RCA: 81] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2015] [Revised: 10/05/2015] [Accepted: 10/28/2015] [Indexed: 12/13/2022]
Abstract
Human influenza viruses cause regular epidemics and occasional pandemics with a substantial public health burden. Household transmission studies have provided valuable information on the dynamics of influenza transmission. We reviewed published studies and found that once one household member is infected with influenza, the risk of infection in a household contact can be up to 38%, and the delay between onset in index and secondary cases is around 3 days. Younger age was associated with higher susceptibility. In the future, household transmission studies will provide information on transmission dynamics, including the correlation of virus shedding and symptoms with transmission, and the correlation of new measures of immunity with protection against infection. Historically, household cohort studies have provided valuable information on the incidence of respiratory infections and risk factors for infection. However, these studies require substantial resources and can provide limited information on transmission dynamics. Household transmission studies provide an efficient approach to describing the risk of influenza transmission and factors affecting transmission. In these studies, households with at least one member infected by influenza are eligible and are followed intensively for 1–2 weeks to observe secondary transmission within the household. Transmission studies also provide a model for evaluation of interventions in randomized controlled trials, and have been used to determine the efficacy of antiviral drugs for treatment and prophylaxis, and nonpharmaceutical interventions such as face masks and hand hygiene.
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Affiliation(s)
- Tim K Tsang
- WHO Collaborating Centre for Infectious Disease Epidemiology and Control, School of Public Health, Li Ka Shing Faculty of Medicine, University of Hong Kong, Hong Kong Special Administrative Region, China
| | - Lincoln L H Lau
- Dalla Lana School of Public Health, University of Toronto, Toronto, Canada
| | - Simon Cauchemez
- Mathematical Modelling of Infectious Diseases Unit, Institut Pasteur, Paris, France
| | - Benjamin J Cowling
- WHO Collaborating Centre for Infectious Disease Epidemiology and Control, School of Public Health, Li Ka Shing Faculty of Medicine, University of Hong Kong, Hong Kong Special Administrative Region, China.
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Jackson ML, Nguyen M, Kirlin B, Madziwa L. Self-Collected Nasal Swabs for Respiratory Virus Surveillance. Open Forum Infect Dis 2015; 2:ofv152. [PMID: 26613095 PMCID: PMC4653956 DOI: 10.1093/ofid/ofv152] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2015] [Accepted: 10/06/2015] [Indexed: 12/04/2022] Open
Abstract
We tested whether 135 patients reporting acute respiratory illness (ARI) could self-collect nasal swab specimens and ship them for laboratory testing. Most subjects (78.2%) collected and shipped their specimens without errors; 10.5% excluded ≥1 packing components; 12.9% made ≥1 packing errors. Self-swabbing at home is feasible for confirming ARI etiology.
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Affiliation(s)
| | | | - Beth Kirlin
- Group Health Research Institute , Seattle, Washington
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11
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Peters TR, Snively BM, Suerken CK, Blakeney E, Vannoy L, Poehling KA. Relative timing of influenza disease by age group. Vaccine 2014; 32:6451-6. [PMID: 25280434 PMCID: PMC4252244 DOI: 10.1016/j.vaccine.2014.09.047] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2014] [Revised: 07/22/2014] [Accepted: 09/22/2014] [Indexed: 11/18/2022]
Abstract
A detailed understanding of influenza movement in communities during yearly epidemics is needed to inform improved influenza control programs. We sought to determine the relative timing of influenza presentation and symptom onset by age group and influenza strain. Prospective, laboratory-confirmed surveillance was performed over three moderate influenza seasons in emergency departments and inpatient settings of both medical centers in Winston-Salem, NC. Influenza disease presented first in school age children through community epidemics of influenza A(H1N1)pdm09 and influenza B, and first in persons 5-49 years old for influenza A(H3N2). This finding indicates that influenza prevention in persons 5-49 years of age may be particularly important in influenza epidemic control.
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Affiliation(s)
- Timothy R Peters
- Department of Pediatrics, Wake Forest School of Medicine, Medical Center Boulevard, Winston-Salem, NC 27157, USA.
| | - Beverly M Snively
- Department of Biostatistical Sciences, Wake Forest School of Medicine, Medical Center Boulevard, Winston-Salem, NC 27157, USA.
| | - Cynthia K Suerken
- Department of Biostatistical Sciences, Wake Forest School of Medicine, Medical Center Boulevard, Winston-Salem, NC 27157, USA.
| | - Elizabeth Blakeney
- Department of Pediatrics, Wake Forest School of Medicine, Medical Center Boulevard, Winston-Salem, NC 27157, USA.
| | - Lauren Vannoy
- Department of Pediatrics, Wake Forest School of Medicine, Medical Center Boulevard, Winston-Salem, NC 27157, USA.
| | - Katherine A Poehling
- Department of Pediatrics, Wake Forest School of Medicine, Medical Center Boulevard, Winston-Salem, NC 27157, USA; Department of Pediatrics and Epidemiology and Prevention, Wake Forest School of Medicine, Medical Center Boulevard, Winston-Salem, NC 27157, USA.
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Khuntirat B, Yoon IK, Chittaganpitch M, Krueger WS, Supawat K, Blair PJ, Putnam SD, Gibbons RV, Buddhari D, Sawanpanyalert P, Heil GL, Friary JA, Gray GC. High rate of A(H1N1)pdm09 infections among rural Thai villagers, 2009-2010. PLoS One 2014; 9:e106751. [PMID: 25188434 PMCID: PMC4154756 DOI: 10.1371/journal.pone.0106751] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2014] [Accepted: 08/09/2014] [Indexed: 11/18/2022] Open
Abstract
Background Pandemic influenza A(H1N1)pdm09 emerged in Thailand in 2009. A prospective longitudinal adult cohort and household transmission study of influenza-like illness (ILI) was ongoing in rural Thailand at the time of emergence. Symptomatic and subclinical A(H1N1)pdm09 infection rates in the cohort and among household members were evaluated. Methods A cohort of 800 Thai adults underwent active community-based surveillance for ILI from 2008–2010. Acute respiratory samples from ILI episodes were tested for A(H1N1)pdm09 by qRT-PCR; acute and 60-day convalescent blood samples were tested by A(H1N1)pdm09 hemagglutination inhibition assay (HI). Enrollment, 12-month and 24-month follow-up blood samples were tested for A(H1N1)pdm09 seroconversion by HI. Household members of influenza A-infected cohort subjects with ILI were enrolled in household transmission investigations in which day 0 and 60 blood samples and acute respiratory samples were tested by either qRT-PCR or HI for A(H1N1)pdm09. Seroconversion between annual blood samples without A(H1N1)pdm09-positive ILI was considered as subclinical infection. Results The 2-yr cumulative incidence of A(H1N1)pdm09 infection in the cohort in 2009/2010 was 10.8% (84/781) with an annual incidence of 1.2% in 2009 and 9.7% in 2010; 83.3% of infections were subclinical (50% in 2009 and 85.9% in 2010). The 2-yr cumulative incidence was lowest (5%) in adults born ≤1957. The A(H1N1)pdm09 secondary attack rate among household contacts was 47.2% (17/36); 47.1% of these infections were subclinical. The highest A(H1N1)pdm09 secondary attack rate among household contacts (70.6%, 12/17) occurred among children born between 1990 and 2003. Conclusion Subclinical A(H1N1)pdm09 infections in Thai adults occurred frequently and accounted for a greater proportion of all A(H1N1)pdm09 infections than previously estimated. The role of subclinical infections in A(H1N1)pdm09 transmission has important implications in formulating strategies to predict and prevent the spread of A(H1N1)pdm09 and other influenza virus strains.
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Affiliation(s)
- Benjawan Khuntirat
- Department of Virology, Armed Forces Research Institute of Medical Sciences, Bangkok, Thailand
| | - In-Kyu Yoon
- Department of Virology, Armed Forces Research Institute of Medical Sciences, Bangkok, Thailand
| | | | - Whitney S. Krueger
- College of Public Health and Health Professions and Emerging Pathogens Institute, University of Florida, Gainesville, Florida, United States of America
| | - Krongkaew Supawat
- National Institute of Health, Ministry of Public Health, Nonthaburi, Thailand
| | | | - Shannon D. Putnam
- Naval Health Research Center, San Diego, California, United States of America
| | - Robert V. Gibbons
- Department of Virology, Armed Forces Research Institute of Medical Sciences, Bangkok, Thailand
| | - Darunee Buddhari
- Department of Virology, Armed Forces Research Institute of Medical Sciences, Bangkok, Thailand
| | | | - Gary L. Heil
- College of Public Health and Health Professions and Emerging Pathogens Institute, University of Florida, Gainesville, Florida, United States of America
| | - John A. Friary
- College of Public Health and Health Professions and Emerging Pathogens Institute, University of Florida, Gainesville, Florida, United States of America
| | - Gregory C. Gray
- College of Public Health and Health Professions and Emerging Pathogens Institute, University of Florida, Gainesville, Florida, United States of America
- * E-mail:
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Cauchemez S, Ferguson NM, Fox A, Mai LQ, Thanh LT, Thai PQ, Thoang DD, Duong TN, Minh Hoa LN, Tran Hien N, Horby P. Determinants of influenza transmission in South East Asia: insights from a household cohort study in Vietnam. PLoS Pathog 2014; 10:e1004310. [PMID: 25144780 PMCID: PMC4140851 DOI: 10.1371/journal.ppat.1004310] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2013] [Accepted: 06/30/2014] [Indexed: 11/18/2022] Open
Abstract
To guide control policies, it is important that the determinants of influenza transmission are fully characterized. Such assessment is complex because the risk of influenza infection is multifaceted and depends both on immunity acquired naturally or via vaccination and on the individual level of exposure to influenza in the community or in the household. Here, we analyse a large household cohort study conducted in 2007–2010 in Vietnam using innovative statistical methods to ascertain in an integrative framework the relative contribution of variables that influence the transmission of seasonal (H1N1, H3N2, B) and pandemic H1N1pdm09 influenza. Influenza infection was diagnosed by haemagglutination-inhibition (HI) antibody assay of paired serum samples. We used a Bayesian data augmentation Markov chain Monte Carlo strategy based on digraphs to reconstruct unobserved chains of transmission in households and estimate transmission parameters. The probability of transmission from an infected individual to another household member was 8% (95% CI, 6%, 10%) on average, and varied with pre-season titers, age and household size. Within households of size 3, the probability of transmission from an infected member to a child with low pre-season HI antibody titers was 27% (95% CI 21%–35%). High pre-season HI titers were protective against infection, with a reduction in the hazard of infection of 59% (95% CI, 44%–71%) and 87% (95% CI, 70%–96%) for intermediate (1∶20–1∶40) and high (≥1∶80) HI titers, respectively. Even after correcting for pre-season HI titers, adults had half the infection risk of children. Twenty six percent (95% CI: 21%, 30%) of infections may be attributed to household transmission. Our results highlight the importance of integrated analysis by influenza sub-type, age and pre-season HI titers in order to infer influenza transmission risks in and outside of the household. Influenza causes an estimated three to five million severe illnesses worldwide each year. In order to guide control policies it is important to determine the key risk factors for transmission. This is often done by studying transmission in households but in the past, analysis of such data has suffered from important simplifying assumptions (for example not being able to account for the effect of biological markers of protection like pre-season antibody titers). We have developed new statistical methods that address these limitations and applied them to a large household cohort study conducted in 2007–2010 in Vietnam. By comparing a large range of model variants, we have obtained unique insights into the patterns and determinants of transmission of seasonal (H1N1, H3N2, B) and pandemic H1N1pdm09 influenza in South East Asia. This includes estimating the proportion of cases attributed to household transmission, the average household transmission probability, the protection afforded by pre-season HI titers, and the effect of age on infection risk after correcting for pre-season HI titers.
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Affiliation(s)
- Simon Cauchemez
- Mathematical Modelling of Infectious Diseases Unit, Institut Pasteur, Paris, France
- MRC Centre for Outbreak Analysis and Modelling, Department of Infectious Disease Epidemiology, Imperial College London, London, United Kingdom
- * E-mail:
| | - Neil M. Ferguson
- MRC Centre for Outbreak Analysis and Modelling, Department of Infectious Disease Epidemiology, Imperial College London, London, United Kingdom
| | - Annette Fox
- Oxford University Clinical Research Unit - Wellcome Trust Major Overseas Programme, Hanoi, Vietnam
- Department of Microbiology and Immunology, University of Melbourne, Melbourne, Australia
| | - Le Quynh Mai
- National Institute of Hygiene and Epidemiology, Hanoi, Vietnam
| | - Le Thi Thanh
- National Institute of Hygiene and Epidemiology, Hanoi, Vietnam
| | - Pham Quang Thai
- National Institute of Hygiene and Epidemiology, Hanoi, Vietnam
| | | | - Tran Nhu Duong
- National Institute of Hygiene and Epidemiology, Hanoi, Vietnam
| | - Le Nguyen Minh Hoa
- Oxford University Clinical Research Unit - Wellcome Trust Major Overseas Programme, Hanoi, Vietnam
| | | | - Peter Horby
- Oxford University Clinical Research Unit - Wellcome Trust Major Overseas Programme, Hanoi, Vietnam
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Chao DY, Cheng KF, Hsieh YH, Li TC, Wu TN, Chen CY. Geographical heterogeneity and influenza infection within households. BMC Infect Dis 2014; 14:369. [PMID: 24993483 PMCID: PMC4094897 DOI: 10.1186/1471-2334-14-369] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2014] [Accepted: 06/30/2014] [Indexed: 11/29/2022] Open
Abstract
Background Although it has been suggested that schoolchildren vaccination reduces influenza morbidity and mortality in the community, it is unknown whether geographical heterogeneity would affect vaccine effectiveness. Methods A 3-year prospective, non-randomized sero-epidemiological study was conducted during 2008–2011 by recruiting schoolchildren from both urban and rural areas. Respective totals of 124, 206, and 176 households were recruited and their household contacts were followed. Serum samples were collected pre-vaccination, one-month post-vaccination and post-season from children and household contacts for hemagglutination inhibition (HI) assay. A multivariate logistic model implemented with generalized estimation equations (GEE) was fitted with morbidity or a four-fold increase in HI titer of the household contacts for two consecutive sera as the dependent variable; with geographical location, vaccination status of each household and previous vaccination history as predictor variables. Results Although our results show no significant reduction in the proportion of infection or clinical morbidity among household contacts, a higher risk of infection, indicated by odds ratio > 1, was consistently observed among household children contacts from the un-vaccinated households after adjusting for confounding variables. Interestingly, a statistically significant lower risk of infection was observed among household adult contacts from rural area when compared to those from urban area (OR = 0.89; 95% CI: 0.82-0.97 for Year 2 and OR = 0.85; 95% CI: 0.75-0.96 for Year 3). Conclusions A significant difference in the risk of influenza infection among household adults due to geographical heterogeneity, independent of schoolchildren vaccination status, was revealed in this study. Its impact on vaccine effectiveness requires further study.
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Affiliation(s)
- Day-Yu Chao
- Graduate Institute of Microbiology and Public Health, College of Veterinary Medicine, National Chung-Hsing University, Taichung, Taiwan.
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15
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Borse RH, Shrestha SS, Fiore AE, Atkins CY, Singleton JA, Furlow C, Meltzer MI. Effects of vaccine program against pandemic influenza A(H1N1) virus, United States, 2009-2010. Emerg Infect Dis 2013; 19:439-48. [PMID: 23622679 PMCID: PMC3647645 DOI: 10.3201/eid1903.120394] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Vaccination likely prevented 700,000–1,500,000 clinical cases, 4,000–10,000 hospitalizations, and 200–500 deaths. In April 2009, the United States began a response to the emergence of a pandemic influenza virus strain: A(H1N1)pdm09. Vaccination began in October 2009. By using US surveillance data (April 12, 2009–April 10, 2010) and vaccine coverage estimates (October 3, 2009–April 18, 2010), we estimated that the A(H1N1)pdm09 virus vaccination program prevented 700,000–1,500,000 clinical cases, 4,000–10,000 hospitalizations, and 200–500 deaths. We found that the national health effects were greatly influenced by the timing of vaccine administration and the effectiveness of the vaccine. We estimated that recommendations for priority vaccination of targeted priority groups were not inferior to other vaccination prioritization strategies. These results emphasize the need for relevant surveillance data to facilitate a rapid evaluation of vaccine recommendations and effects.
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Affiliation(s)
- Rebekah H Borse
- Centers for Disease Control and Prevention, Atlanta, GA 30333, USA
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Jartti T, Söderlund-Venermo M, Hedman K, Ruuskanen O, Mäkelä MJ. New molecular virus detection methods and their clinical value in lower respiratory tract infections in children. Paediatr Respir Rev 2013; 14:38-45. [PMID: 23347659 PMCID: PMC7106250 DOI: 10.1016/j.prrv.2012.04.002] [Citation(s) in RCA: 72] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
During the past decade, several new respiratory viruses and their subgroups have been discovered. All these new viruses, as well as previously known respiratory viruses, can be detected by sensitive PCR methods, which have become popular in the diagnostic workup of respiratory viral infections. Currently, respiratory viruses can be detected in up to 95% of children with lower respiratory tract illness. On the other hand, virus detection rates in asymptomatic children are also high (up to 68%), as are coinfection rates in symptomatic children (up to 43%) and justified concerns of causality have been raised. Imposing progress has been made in developing multiplex quantitative PCR assays; here, several primer sets are run within a single PCR mixture. These PCR assays give a better understanding of the dominant viral infection, of viral infections that may be incipient and of any waning infections than does a single-target PCR. Multiplex PCR assays are also gaining popularity due to their cost-effectiveness and short throughput time compared to multiple single-target PCRs. Our understanding of the indications of virus PCRs and our ability to interpret the results from a clinical point of view have improved. This paper reviews the progress in PCR assays and discusses their role in the diagnosis of lower respiratory tract infections in children.
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Key Words
- dna, deoxyribonucleic acid
- hbov, human bocavirus
- hmpv, human metapneumovirus
- hrv, human rhinovirus
- lrti, lower respiratory tract illness
- n, number of samples
- np, nasophryngeal
- npa, nasopharyngeal aspirate
- pcr, polymerase chain reaction
- piv, parainfluenza virus
- qpcr, quantitative pcr
- rna, ribonucleic acid
- rsv, respiratory syncytial virus
- rt, reverse transcriptase
- rvp, respiratory virus panel
- child
- infection
- lower respiratory tract
- multiplex
- pcr
- quantitative
- respiratory
- virus
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Affiliation(s)
- Tuomas Jartti
- Department of Pediatrics, Turku University Hospital, Turku, Finland.
| | | | - Klaus Hedman
- Department of Virology; University of Helsinki; Helsinki
| | - Olli Ruuskanen
- Department of Pediatrics, Turku University Hospital, Turku
| | - Mika J. Mäkelä
- Pediatric division, Department of Allergy, Skin and Allergy Hospital, University of Helsinki, Helsinki, all in Finland
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Laurie KL, Huston P, Riley S, Katz JM, Willison DJ, Tam JS, Mounts AW, Hoschler K, Miller E, Vandemaele K, Broberg E, Van Kerkhove MD, Nicoll A. Influenza serological studies to inform public health action: best practices to optimise timing, quality and reporting. Influenza Other Respir Viruses 2013; 7:211-24. [PMID: 22548725 PMCID: PMC5855149 DOI: 10.1111/j.1750-2659.2012.0370a.x] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
BACKGROUND Serological studies can detect infection with a novel influenza virus in the absence of symptoms or positive virology, providing useful information on infection that goes beyond the estimates from epidemiological, clinical and virological data. During the 2009 A(H1N1) pandemic, an impressive number of detailed serological studies were performed, yet the majority of serological data were available only after the first wave of infection. This limited the ability to estimate the transmissibility and severity of this novel infection, and the variability in methodology and reporting limited the ability to compare and combine the serological data. OBJECTIVES To identify best practices for conduct and standardisation of serological studies on outbreak and pandemic influenza to inform public policy. METHODS/SETTING An international meeting was held in February 2011 in Ottawa, Canada, to foster the consensus for greater standardisation of influenza serological studies. RESULTS Best practices for serological investigations of influenza epidemiology include the following: classification of studies as pre-pandemic, outbreak, pandemic or inter-pandemic with a clearly identified objective; use of international serum standards for laboratory assays; cohort and cross-sectional study designs with common standards for data collection; use of serum banks to improve sampling capacity; and potential for linkage of serological, clinical and epidemiological data. Advance planning for outbreak studies would enable a rapid and coordinated response; inclusion of serological studies in pandemic plans should be considered. CONCLUSIONS Optimising the quality, comparability and combinability of influenza serological studies will provide important data upon emergence of a novel or variant influenza virus to inform public health action.
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Affiliation(s)
- Karen L Laurie
- WHO Collaborating Centre for Reference and Research on Influenza, VIDRL, North Melbourne, Vic. 3051, Australia.
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Kang EK, Lim JS, Lee JA, Kim DH. Comparison of immune response by virus infection and vaccination to 2009 pandemic influenza A/H1N1 in children. J Korean Med Sci 2013; 28:274-9. [PMID: 23399558 PMCID: PMC3565140 DOI: 10.3346/jkms.2013.28.2.274] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/22/2012] [Accepted: 11/26/2012] [Indexed: 11/20/2022] Open
Abstract
We aimed to compare the immune response induced by natural infection with 2009 pandemic influenza A/H1N1 (pH1N1) virus and by monovalent pH1N1 vaccination in children and adolescents. This cross-sectional clinical study was conducted at 3 hospitals in Korea from February to May 2010. A total of 266 healthy subjects aged from 6 months to 18 yr were tested for the presence of the antibody against pH1N1 using hemagglutination inhibition (HI) test. Information about pH1N1 vaccination and laboratory-confirmed pH1N1 infection history was obtained. The overall rate of HI titers of ≥ 1:40 against pH1N1 was 38.7%, and the geometric mean titer (GMT) was 20.5. Immunogenicity of pH1N1 vaccination only was reflected by a 41.1% of seroprotection rate and a GMT of 22.5. Immunogenicity of natural infection only was reflected by a 61.0% of seroprotection rate and a GMT of 40.0. GMT was significantly higher in the subjects of natural infection group than in the subjects of pH1N1 vaccination group (P < 0.001). The immune responses induced by natural pH1N1 infection exceed those induced by pH1N1 vaccinations.
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Affiliation(s)
- Eun Kyeong Kang
- Department of Pediatrics, Dongguk University Ilsan Hospital, Goyang, Korea
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Mizumoto K, Nishiura H, Yamamoto T. Effectiveness of antiviral prophylaxis coupled with contact tracing in reducing the transmission of the influenza A (H1N1-2009): a systematic review. Theor Biol Med Model 2013; 10:4. [PMID: 23324555 PMCID: PMC3563494 DOI: 10.1186/1742-4682-10-4] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2012] [Accepted: 01/14/2013] [Indexed: 01/08/2023] Open
Abstract
BACKGROUND During the very early stage of the 2009 pandemic, mass chemoprophylaxis was implemented as part of containment measure. The purposes of the present study were to systematically review the retrospective studies that investigated the effectiveness of antiviral prophylaxis during the 2009 pandemic, and to explicitly estimate the effectiveness by employing a mathematical model. METHODS A systematic review identified 17 articles that clearly defined the cases and identified exposed individuals based on contact tracing. Analysing a specific school-driven outbreak, we estimated the effectiveness of antiviral prophylaxis using a renewal equation model. Other parameters, including the reproduction number and the effectiveness of antiviral treatment and school closure, were jointly estimated. RESULTS Based on the systematic review, median secondary infection risks (SIRs) among exposed individuals with and without prophylaxis were estimated at 2.1% (quartile: 0, 12.2) and 16.6% (quartile: 8.4, 32.4), respectively. A very high heterogeneity in the SIR was identified with an estimated I2 statistic at 71.8%. From the outbreak data in Madagascar, the effectiveness of mass chemoprophylaxis in reducing secondary transmissions was estimated to range from 92.8% to 95.4% according to different model assumptions and likelihood functions, not varying substantially as compared to other parameters. CONCLUSIONS Only based on the meta-analysis of retrospective studies with different study designs and exposure settings, it was not feasible to estimate the effectiveness of antiviral prophylaxis in reducing transmission. However, modelling analysis of a single outbreak successfully yielded an estimate of the effectiveness that appeared to be robust to model assumptions. Future studies should fill the data gap that has existed in observational studies and allow mathematical models to be used for the analysis of meta-data.
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Affiliation(s)
- Kenji Mizumoto
- School of Public Health, The University of Hong Kong, 100 Cyberport Road, Pokfulam, Hong Kong, China
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20
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Soh SE, Cook AR, Chen MIC, Lee VJ, Cutter JL, Chow VTK, Tee NWS, Lin RTP, Lim WY, Barr IG, Lin C, Phoon MC, Ang LW, Sethi SK, Chong CY, Goh LG, Goh DLM, Tambyah PA, Thoon KC, Leo YS, Saw SM. Teacher led school-based surveillance can allow accurate tracking of emerging infectious diseases - evidence from serial cross-sectional surveys of febrile respiratory illness during the H1N1 2009 influenza pandemic in Singapore. BMC Infect Dis 2012; 12:336. [PMID: 23206689 PMCID: PMC3544582 DOI: 10.1186/1471-2334-12-336] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2011] [Accepted: 11/06/2012] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Schools are important foci of influenza transmission and potential targets for surveillance and interventions. We compared several school-based influenza monitoring systems with clinic-based influenza-like illness (ILI) surveillance, and assessed the variation in illness rates between and within schools. METHODS During the initial wave of pandemic H1N1 (pdmH1N1) infections from June to Sept 2009 in Singapore, we collected data on nation-wide laboratory confirmed cases (Sch-LCC) and daily temperature monitoring (Sch-DTM), and teacher-led febrile respiratory illness reporting in 6 sentinel schools (Sch-FRI). Comparisons were made against age-stratified clinic-based influenza-like illness (ILI) data from 23 primary care clinics (GP-ILI) and proportions of ILI testing positive for pdmH1N1 (Lab-ILI) by computing the fraction of cumulative incidence occurring by epidemiological week 30 (when GP-ILI incidence peaked); and cumulative incidence rates between school-based indicators and sero-epidemiological pdmH1N1 incidence (estimated from changes in prevalence of A/California/7/2009 H1N1 hemagglutination inhibition titers ≥ 40 between pre-epidemic and post-epidemic sera). Variation in Sch-FRI rates in the 6 schools was also investigated through a Bayesian hierarchical model. RESULTS By week 30, for primary and secondary school children respectively, 63% and 79% of incidence for Sch-LCC had occurred, compared with 50% and 52% for GP-ILI data, and 48% and 53% for Sch-FRI. There were 1,187 notified cases and 7,588 episodes in the Sch-LCC and Sch-DTM systems; given school enrollment of 485,723 children, this represented 0.24 cases and 1.6 episodes per 100 children respectively. Mean Sch-FRI rate was 28.8 per 100 children (95% CI: 27.7 to 29.9) in the 6 schools. We estimate from serology that 41.8% (95% CI: 30.2% to 55.9%) of primary and 43.2% (95% CI: 28.2% to 60.8%) of secondary school-aged children were infected. Sch-FRI rates were similar across the 6 schools (23 to 34 episodes per 100 children), but there was widespread variation by classrooms; in the hierarchical model, omitting age and school effects was inconsequential but neglecting classroom level effects led to highly significant reductions in goodness of fit. CONCLUSIONS Epidemic curves from Sch-FRI were comparable to GP-ILI data, and Sch-FRI detected substantially more infections than Sch-LCC and Sch-DTM. Variability in classroom attack rates suggests localized class-room transmission.
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Affiliation(s)
- Shu E Soh
- National University of Singapore, 21 Lower Kent Ridge Road, Singapore 119077, Singapore
| | - Alex R Cook
- National University of Singapore, 21 Lower Kent Ridge Road, Singapore 119077, Singapore
| | - Mark IC Chen
- National University of Singapore, 21 Lower Kent Ridge Road, Singapore 119077, Singapore
- Communicable Disease Centre, Tan Tock Seng Hospital, 11 Jalan Tan Tock Seng, Singapore 308433, Singapore
- Duke-NUS Graduate Medical School, 8 College Road, Singapore, 169857, Singapore
- Department of Clinical Epidemiology, Tan Tock Seng Hospital, 11 Jalan Tan Tock Seng, Singapore, 308433, Singapore
| | - Vernon J Lee
- National University of Singapore, 21 Lower Kent Ridge Road, Singapore 119077, Singapore
- Ministry of Defence, Gombak Drive, Singapore, 669645, Singapore
| | - Jeffery L Cutter
- Ministry of Health, College of Medicine Building, 16 College Road, Singapore, 169854, Singapore
| | - Vincent TK Chow
- National University of Singapore, 21 Lower Kent Ridge Road, Singapore 119077, Singapore
| | - Nancy WS Tee
- KK Women’s and Children’s Hospital, 100 Bukit Timah Road, Singapore, 229899, Singapore
| | - Raymond TP Lin
- Ministry of Health, College of Medicine Building, 16 College Road, Singapore, 169854, Singapore
| | - Wei-Yen Lim
- National University of Singapore, 21 Lower Kent Ridge Road, Singapore 119077, Singapore
| | - Ian G Barr
- World Health Organization Collaborating Centre for Reference and Research on Influenza, 10 Wreckyn Street, North Melbourne, VIC, 3051, Australia
| | - Cui Lin
- Ministry of Health, College of Medicine Building, 16 College Road, Singapore, 169854, Singapore
| | - Meng Chee Phoon
- National University of Singapore, 21 Lower Kent Ridge Road, Singapore 119077, Singapore
| | - Li Wei Ang
- Ministry of Health, College of Medicine Building, 16 College Road, Singapore, 169854, Singapore
| | - Sunil K Sethi
- National University Health Systems, 1E Kent Ridge Road, Singapore, 119228, Singapore
| | - Chia Yin Chong
- KK Women’s and Children’s Hospital, 100 Bukit Timah Road, Singapore, 229899, Singapore
| | - Lee Gan Goh
- National University Health Systems, 1E Kent Ridge Road, Singapore, 119228, Singapore
| | - Denise LM Goh
- National University Health Systems, 1E Kent Ridge Road, Singapore, 119228, Singapore
| | - Paul A Tambyah
- National University Health Systems, 1E Kent Ridge Road, Singapore, 119228, Singapore
| | - Koh Cheng Thoon
- KK Women’s and Children’s Hospital, 100 Bukit Timah Road, Singapore, 229899, Singapore
| | - Yee Sin Leo
- Communicable Disease Centre, Tan Tock Seng Hospital, 11 Jalan Tan Tock Seng, Singapore 308433, Singapore
- Department of Clinical Epidemiology, Tan Tock Seng Hospital, 11 Jalan Tan Tock Seng, Singapore, 308433, Singapore
| | - Seang Mei Saw
- National University of Singapore, 21 Lower Kent Ridge Road, Singapore 119077, Singapore
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Glatman-Freedman A, Portelli I, Jacobs SK, Mathew JI, Slutzman JE, Goldfrank LR, Smith SW. Attack rates assessment of the 2009 pandemic H1N1 influenza A in children and their contacts: a systematic review and meta-analysis. PLoS One 2012; 7:e50228. [PMID: 23284603 PMCID: PMC3523802 DOI: 10.1371/journal.pone.0050228] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2012] [Accepted: 10/18/2012] [Indexed: 11/30/2022] Open
Abstract
BACKGROUND The recent H1N1 influenza A pandemic was marked by multiple reports of illness and hospitalization in children, suggesting that children may have played a major role in the propagation of the virus. A comprehensive detailed analysis of the attack rates among children as compared with their contacts in various settings is of great importance for understanding their unique role in influenza pandemics. METHODOLOGY/PRINCIPAL FINDINGS We searched MEDLINE (PubMed) and Embase for published studies reporting outbreak investigations with direct measurements of attack rates of the 2009 pandemic H1N1 influenza A among children, and quantified how these compare with those of their contacts. We identified 50 articles suitable for review, which reported school, household, travel and social events. The selected reports and our meta-analysis indicated that children had significantly higher attack rates as compared to adults, and that this phenomenon was observed for both virologically confirmed and clinical cases, in various settings and locations around the world. The review also provided insight into some characteristics of transmission between children and their contacts in the various settings. CONCLUSION/SIGNIFICANCE The consistently higher attack rates of the 2009 pandemic H1N1 influenza A among children, as compared to adults, as well as the magnitude of the difference is important for understanding the contribution of children to disease burden, for implementation of mitigation strategies directed towards children, as well as more precise mathematical modeling and simulation of future influenza pandemics.
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Affiliation(s)
- Aharona Glatman-Freedman
- Department of Family and Community Medicine, New York Medical College, Valhalla, New York, United States of America.
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Prevalence of seropositivity to pandemic influenza A/H1N1 virus in the United States following the 2009 pandemic. PLoS One 2012; 7:e48187. [PMID: 23118949 PMCID: PMC3485186 DOI: 10.1371/journal.pone.0048187] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2012] [Accepted: 09/24/2012] [Indexed: 11/21/2022] Open
Abstract
Background 2009 pandemic influenza A/H1N1 (A(H1N1)pdm09) was first detected in the United States in April 2009 and resulted in a global pandemic. We conducted a serologic survey to estimate the cumulative incidence of A(H1N1)pdm09 through the end of 2009 when pandemic activity had waned in the United States. Methods We conducted a pair of cross sectional serologic surveys before and after the spring/fall waves of the pandemic for evidence of seropositivity (titer ≥40) using the hemagglutination inhibition (HI) assay. We tested a baseline sample of 1,142 serum specimens from the 2007–2008 National Health and Nutrition Examination Survey (NHANES), and 2,759 serum specimens submitted for routine screening to clinical diagnostic laboratories from ten representative sites. Results The age-adjusted prevalence of seropositivity to A(H1N1)pdm09 by year-end 2009 was 36.9% (95%CI: 31.7–42.2%). After adjusting for baseline cross-reactive antibody, pandemic vaccination coverage and the sensitivity/specificity of the HI assay, we estimate that 20.2% (95%CI: 10.1–28.3%) of the population was infected with A(H1N1)pdm09 by December 2009, including 53.3% (95%CI: 39.0–67.1%) of children aged 5–17 years. Conclusions By December 2009, approximately one-fifth of the US population, or 61.9 million persons, may have been infected with A(H1N1)pdm09, including around half of school-aged children.
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House T, Inglis N, Ross JV, Wilson F, Suleman S, Edeghere O, Smith G, Olowokure B, Keeling MJ. Estimation of outbreak severity and transmissibility: Influenza A(H1N1)pdm09 in households. BMC Med 2012; 10:117. [PMID: 23046520 PMCID: PMC3520767 DOI: 10.1186/1741-7015-10-117] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/22/2012] [Accepted: 10/09/2012] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND When an outbreak of a novel pathogen occurs, some of the most pressing questions from a public-health point of view relate to its transmissibility, and the probabilities of different clinical outcomes following infection, to allow an informed response. Estimates of these quantities are often based on household data due to the high potential for transmission in this setting, but typically a rich spectrum of individual-level outcomes (from uninfected to serious illness) are simplified to binary data (infected or not). We address the added benefit from retaining the heterogeneous outcome information in the case of the 2009-10 influenza pandemic, which posed particular problems for estimation of key epidemiological characteristics due to its relatively mild nature and hence low case ascertainment rates. METHODS We use mathematical models of within-household transmission and case ascertainment, together with Bayesian statistics to estimate transmission probabilities stratified by household size, the variability of infectiousness of cases, and a set of probabilities describing case ascertainment. This novel approach was applied to data we collected from the early "containment phase" stage of the epidemic in Birmingham, England. We also conducted a comprehensive review of studies of household transmission of influenza A(H1N1)pdm09. RESULTS We find large variability in the published estimates of within-household transmissibility of influenza A(H1N1)pdm09 in both model-based studies and those reporting secondary attack rates, finding that these estimates are very sensitive to how an infected case is defined. In particular, we find that reliance on laboratory confirmation alone underestimates the true number of cases, while utilising the heterogeneous range of outcomes (based on case definitions) for household infections allows a far more comprehensive pattern of transmission to be elucidated. CONCLUSIONS Differences in household sizes and how cases are defined could account for an appreciable proportion of the reported variability of within-household transmissibility of influenza A(H1N1)pdm09. Retaining and statistically analysing the full spectrum of individual-level outcomes (based on case definitions) rather than taking a potentially arbitrary threshold for infection, provides much-needed additional information. In a future pandemic, our approach could be used as a real-time analysis tool to infer the true number of cases, within-household transmission rates and levels of case ascertainment.
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Affiliation(s)
- Thomas House
- Mathematics Institute, University of Warwick, Coventry, CV4 7AL, UK.
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Household transmission of 2009 pandemic influenza A (H1N1): a systematic review and meta-analysis. Epidemiology 2012; 23:531-42. [PMID: 22561117 DOI: 10.1097/ede.0b013e31825588b8] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
BACKGROUND During the 2009 influenza A (H1N1) pandemic, household transmission studies were implemented to better understand the characteristics of the transmission of the novel virus in a confined setting. METHODS We conducted a systematic review and meta-analysis to assess and summarize the findings of these studies. We identified 27 articles, around half of which reported studies conducted in May and June 2009. RESULTS In 13 of the 27 studies (48%) that collected respiratory specimens from household contacts, point estimates of the risk of secondary infection ranged from 3% to 38%, with substantial heterogeneity. Meta-regression analyses revealed that a part of the heterogeneity reflected varying case ascertainment and study designs. The estimates of symptomatic secondary infection risk, based on 20 studies identifying febrile acute respiratory illness among household contacts, also showed substantial variability, with point estimates ranging from 4% to 37%. CONCLUSIONS Transmission of the 2009 pandemic virus in households appeared to vary among countries and settings, with differences in estimates of the secondary infection risk also partly due to differences in study designs.
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Fisher BM, Van Bockern J, Hart J, Lynch AM, Winn VD, Gibbs RS, Weinberg A. Pandemic influenza A H1N1 2009 infection versus vaccination: a cohort study comparing immune responses in pregnancy. PLoS One 2012; 7:e33048. [PMID: 22457731 PMCID: PMC3310855 DOI: 10.1371/journal.pone.0033048] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2011] [Accepted: 02/09/2012] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND With the emergence of H1N1 pandemic (pH1N1) influenza, the CDC recommended that pregnant women be one of five initial target groups to receive the 2009 monovalent H1N1 vaccine, regardless of prior infection with this influenza strain. We sought to compare the immune response of pregnant women to H1N1 infection versus vaccination and to determine the extent of passive immunity conferred to the newborn. METHODS/FINDINGS During the 2009-2010 influenza season, we enrolled a cohort of women who either had confirmed pH1N1 infection during pregnancy, did not have pH1N1 during pregnancy but were vaccinated against pH1N1, or did not have illness or vaccination. Maternal and umbilical cord venous blood samples were collected at delivery. Hemagglutination inhibition assays (HAI) for pH1N1 were performed. Data were analyzed using linear regression analyses. HAIs were performed for matched maternal/cord blood pairs for 16 women with confirmed pH1N1 infection, 14 women vaccinated against pH1N1, and 10 women without infection or vaccination. We found that pH1N1 vaccination and wild-type infection during pregnancy did not differ with respect to (1) HAI titers at delivery, (2) HAI antibody decay slopes over time, and (3) HAI titers in the cord blood. CONCLUSIONS Vaccination against pH1N1 confers a similar HAI antibody response as compared to pH1N1 infection during pregnancy, both in quantity and quality. Illness or vaccination during pregnancy confers passive immunity to the newborn.
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Affiliation(s)
- Barbra M. Fisher
- Department of Obstetrics and Gynecology, Section of Maternal-Fetal Medicine, University of Colorado School of Medicine, Aurora, Colorado, United States of America
| | - Janice Van Bockern
- Department of Obstetrics and Gynecology, Section of Maternal-Fetal Medicine, University of Colorado School of Medicine, Aurora, Colorado, United States of America
| | - Jan Hart
- Department of Obstetrics and Gynecology, Section of Maternal-Fetal Medicine, University of Colorado School of Medicine, Aurora, Colorado, United States of America
| | - Anne M. Lynch
- Department of Obstetrics and Gynecology, Section of Maternal-Fetal Medicine, University of Colorado School of Medicine, Aurora, Colorado, United States of America
| | - Virginia D. Winn
- Department of Obstetrics and Gynecology, Section of Maternal-Fetal Medicine, University of Colorado School of Medicine, Aurora, Colorado, United States of America
| | - Ronald S. Gibbs
- Department of Obstetrics and Gynecology, Section of Maternal-Fetal Medicine, University of Colorado School of Medicine, Aurora, Colorado, United States of America
- Novartis Diagnostics and Therapeutics, Emeryville, California, United States of America
| | - Adriana Weinberg
- Departments of Pediatrics, Medicine, and Pathology, University of Colorado School of Medicine, Aurora, Colorado, United States of America
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