Detecting Spread of Avian Influenza A(H7N9) Virus Beyond China

Abstract

During February 2013-March 2015, a total of 602 human cases of low pathogenic avian influenza A(H7N9) were reported; no autochthonous cases were reported outside mainland China. In contrast, since highly pathogenic avian influenza A(H5N1) reemerged during 2003 in China, 784 human cases in 16 countries and poultry outbreaks in 53 countries have been reported. Whether the absence of reported A(H7N9) outside mainland China represents lack of spread or lack of detection remains unclear. We compared epidemiologic and virologic features of A(H5N1) and A(H7N9) and used human and animal influenza surveillance data collected during April 2013-May 2014 from 4 Southeast Asia countries to assess the likelihood that A(H7N9) would have gone undetected during 2014. Surveillance in Vietnam and Cambodia detected human A(H5N1) cases; no A(H7N9) cases were detected in humans or poultry in Southeast Asia. Although we cannot rule out the possible spread of A(H7N9), substantial spread causing severe disease in humans is unlikely.

Keywords: A(H5N1); A(H7N9); Cambodia; China; Influenza; Laos; Southeast Asia; Thailand; Vietnam; poultry; respiratory infections; surveillance; viruses.

Figure 1

Avian influenza A(H7N9) in humans, China, 2013–2014. Data were obtained from the World Health Organization as reported from the National Health and Family Planning Commission (http://www.who.int/influenza/human_animal_interface/influenza_h7n9/en/).

Figure 2

Initial 2-year spread of human cases and poultry outbreaks of influenza A(H5N1) in China and Southeast Asia, December 2003–2005. Data on A(H5N1) in humans were obtained from the World Health Organization (http://www.who.int/influenza/human_animal_interface/en/). Data on outbreaks of A(H5N1) in poultry were obtained from the World Organisation for Animal Health (outbreaks before 2005 from http://www.oie.int/en/animal-health-in-the-world/the-world-animal-health-information-system/data-before-2005-handistatus/; outbreaks after 2005 from http://www.oie.int/wahis_2/public/wahid.php/Wahidhome/Home).

Figure 3

Severe acute respiratory infection (SARI) and influenza-like Illness (ILI) sentinel sites in Vietnam, Thailand, Laos, and Cambodia. A given location might have >1 SARI or ILI sentinel site. SARI sites in Laos include planned SARI sites and 8 nonsentinel SARI sites. (The Lang Son and Quang Ninh province sites continue to operate. The Hanoi site operated until June 2014.)