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PLoS One. 2014 Sep 12;9(9):e106171. doi: 10.1371/journal.pone.0106171. eCollection 2014.

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

Author information

1
Quantitative Sciences Unit, Stanford University Department of Medicine, Stanford, California, United States of America.
2
Division of Pulmonary and Critical Care Medicine, Stanford University Medical Center, Stanford, California, United States of America.
3
Kaiser Permanente Southern California, Pasadena, California, United States of America.
4
Influenza Division, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, United States of America.
5
Center for Health Policy and Center for Primary Care and Outcomes Research, Stanford University, Stanford, California, United States of America.
6
Department of Languages, Literatures, and Cultures, University of South Carolina, Columbia, South Carolina, United States of America.
7
Division of Pulmonary and Critical Care Medicine, Stanford University Medical Center, Stanford, California, United States of America; Center for Health Policy and Center for Primary Care and Outcomes Research, Stanford University, Stanford, California, United States of America.

Abstract

BACKGROUND:

Human 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.

METHODS:

We 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.

FINDINGS:

We 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.

INTERPRETATION:

Across 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.

PMID:
25215608
PMCID:
PMC4162536
DOI:
10.1371/journal.pone.0106171
[Indexed for MEDLINE]
Free PMC Article

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