Global epidemiology of avian influenza A H5N1 virus infection in humans, 1997–2015: a systematic review of individual case data

Journal article

Background From November 2014 through April 2015, there were a total of 165 confirmed human cases of avian influenza A(H5N1) virus infection, including 48 deaths that were reported to the World Health Organization (WHO). This is the highest number of human cases ever reported globally over a similar period since the first human case of H5N1 was reported in Hong Kong in 1997. This study describes the epidemiology of human cases of H5N1 in 1997-2015. Methods We describe the epidemiology of global human H5N1 cases spanning 18 years between 1 May 1997 and 30 April 2015, focusing on the characteristics of cases, seasonality, geographical distribution, and outcome. Findings A total of 907 human H5N1 cases were reported globally from May 1997 to April 2015, with no cases reported between 1998 and 2002, and the largest annual numbers recorded in 2015 (152 cases). The number of affected countries rose between 2003 and 2008, with expansion from East and Southeast Asia, then to West Asia and Africa. The overall case fatality risk (CFR) was 53.5%, and this varied across geographical regions (p<0.001) with the highest (69.4%) in East and Southeast Asia and the lowest in North Africa (32.1%). The age of cases differed significantly by outcome (p<0.001), with a median age of 22 years for fatal cases and 10 years for non-fatal cases. The majority (95.8%, 748/781) of cases reported exposure to poultry. Although the incidence of human cases in Egypt has increased dramatically from November 2014 through April 2015, but compared to the cases before November 2014 there were no significant differences in the CFR, history of exposure to poultry, history of human case contact, and time from onset to hospitalization. Interpretation The geographic distribution of countries affected has expanded, especially between 2003 and 2008, with variations in outcome, demography, seasonality and virus clade across regions. The incidence of human infection has increased dramatically in Egypt since November 2014, but the CFR has not changed significantly.

Authors: Lai, S; Qin, Y; Cowling, B; Ren, X; Wardrop, N

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Elsevier
• Journal: Lancet Infectious Diseases
• Volume: 16
• Issue: 7
• Pages: e108-e118
• Publication date: 2016-05-17
• DOI: 10.1016/S1473-3099(16)00153-5
• EISSN: 1474-4457
• ISSN: 1473-3099
• Language: English
• Keywords: H5N1; Egypt; seasonality; epidemiology; avian influenza