Abstract
Co-circulation of influenza A(H5N1) and seasonal influenza viruses among humans and animals could lead to co-infections, reassortment, and emergence of novel viruses with pandemic potential. We assessed the timing of subtype H5N1 outbreaks among poultry, human H5N1 cases, and human seasonal influenza in 8 countries that reported 97% of all human H5N1 cases and 90% of all poultry H5N1 outbreaks. In these countries, most outbreaks among poultry (7,001/11,331, 62%) and half of human cases (313/625, 50%) occurred during January-March. Human H5N1 cases occurred in 167 (45%) of 372 months during which outbreaks among poultry occurred, compared with 59 (10%) of 574 months that had no outbreaks among poultry. Human H5N1 cases also occurred in 59 (22%) of 267 months during seasonal influenza periods. To reduce risk for co-infection, surveillance and control of H5N1 should be enhanced during January-March, when H5N1 outbreaks typically occur and overlap with seasonal influenza virus circulation.
Highlights
Co-circulation of influenza A(H5N1) and seasonal influenza viruses among humans and animals could lead to coinfections, reassortment, and emergence of novel viruses with pandemic potential
We explored whether H5N1 outbreaks among domestic poultry and human H5N1 cases occurred in temporal proximity, occurred during certain climate conditions, or overlapped with human seasonal influenza epidemics
Timing of Human H5N1 Cases and Poultry H5N1 Outbreaks We identified the monthly number of human H5N1 cases reported to the World Health Organization (WHO) during January 2004– June 2013
Summary
Co-circulation of influenza A(H5N1) and seasonal influenza viruses among humans and animals could lead to coinfections, reassortment, and emergence of novel viruses with pandemic potential. To reduce risk for co-infection, surveillance and control of H5N1 should be enhanced during January–March, when H5N1 outbreaks typically occur and overlap with seasonal influenza virus circulation. H5N1 viruses have not yet acquired the ability to be transmitted between humans beyond 3 generations, failing to show sustained human-to-human transmission [8] These viruses have wide geographic distribution and the potential to reassort with human seasonal influenza viruses. These characteristics mean that clarifying the timing of H5N1 outbreaks among poultry and infections in humans may be useful for prevention and control activities. We explored whether H5N1 outbreaks among domestic poultry and human H5N1 cases occurred in temporal proximity, occurred during certain climate conditions, or overlapped with human seasonal influenza epidemics
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