Seasonal patterns in human A (H5N1) virus infection: analysis of global cases.

Maya B Mathur,Timothy M Uyeki,Yang Xiao,Rita B Patel,Michael Gould,Nayer Khazeni,Charlotte Chae,Jay Bhattacharya,Yoshi Gillaspie,Gerardo Chowell

doi:10.1371/journal.pone.0106171

Abstract

BackgroundHuman cases of highly pathogenic avian influenza (HPAI) A (H5N1) have high mortality. Despite abundant data on seasonal patterns in influenza epidemics, it is unknown whether similar patterns exist for human HPAI H5N1 cases worldwide. Such knowledge could help decrease avian-to-human transmission through increased prevention and control activities during peak periods.MethodsWe performed a systematic search of published human HPAI H5N1 cases to date, collecting month, year, country, season, hemisphere, and climate data. We used negative binomial regression to predict changes in case incidence as a function of season. To investigate hemisphere as a potential moderator, we used AIC and the likelihood-ratio test to compare the season-only model to nested models including a main effect or interaction with hemisphere. Finally, we visually assessed replication of seasonal patterns across climate groups based on the Köppen-Geiger climate classification.FindingsWe identified 617 human cases (611 with complete seasonal data) occurring in 15 countries in Southeast Asia, Africa, and the Middle East. Case occurrence was much higher in winter (n = 285, p = 0.03) than summer (n = 64), and the winter peak occurred across diverse climate groups. There was no significant interaction between hemisphere and season.InterpretationAcross diverse climates, HPAI H5N1 virus infection in humans increases significantly in winter. This is consistent with increased poultry outbreaks and HPAI H5N1 virus transmission during cold and dry conditions. Prioritizing prevention and control activities among poultry and focusing public health messaging to reduce poultry exposures during winter months may help to reduce zoonotic transmission of HPAI H5N1 virus in resource-limited settings.

Highlights

With a case-fatality proportion of approximately 60% [1], highly pathogenic avian influenza (HPAI) A (H5N1) virus is a serious public health threat in a number of countries
We investigated seasonal patterns in the occurrence of human cases of HPAI H5N1 using a comprehensive data set comprising all confirmed, symptomatic cases published in the literature since the initial 1997 outbreak in Hong Kong
We compiled our dataset of 611 cases through a systematic search of all published human cases of HPAI H5N1, investigated seasonal incidence patterns in human infections with HPAI H5N1 viruses and explored hemisphere as a potential moderator of seasonal fluctuations in case incidence

Summary

Introduction

With a case-fatality proportion of approximately 60% [1], highly pathogenic avian influenza (HPAI) A (H5N1) virus is a serious public health threat in a number of countries. Isolates from aquatic and terrestrial poultry in mainland China were most frequently HPAI H5N1-positive during winter [7,8], and drops in temperature tend to immediately precede avian outbreaks [9]. Such seasonal patterns among avian vectors suggest similar patterns might exist in human cases. Despite abundant data on seasonal patterns in influenza epidemics, it is unknown whether similar patterns exist for human HPAI H5N1 cases worldwide Such knowledge could help decrease avian-to-human transmission through increased prevention and control activities during peak periods

Methods

Results

Conclusion