Update: Domestic H5 Outbreak in Birds

Investigation into initial human exposures to H5-infected birds suggests risk of human infection is low

July 24, 2015 - - A report published in Emerging Infectious Diseases (EID) today sheds light on the human health risk posed by newly detected highly pathogenic avian influenza H5 viruses in birds in the United States. The investigation identified 164 people exposed to domestic H5 viruses in the United States from December 15, 2014, to March 31, 2015. While some of these exposures included contact with infected birds none have resulted in human infection. These findings support CDC’s current assessment that the risk of human infections from these viruses is relatively currently low.

Avian influenza A H5 viruses were detected in birds in the United States in December 2014. The human exposures described in the paper are among the first in the United States. While the EID report details early human exposures to these viruses, no human infections having been detected at this time.

Of the 164 human exposures described in the EID report, approximately 63% was associated with H5N2 virus, 34% associated with H5N8 virus, and 2% with H5N1 virus.* While the H5N8 viruses detected in the United States are similar to viruses previously found in birds in other countries, the H5N2** and H5N1 viruses detected in U.S. birds are new reassortant viruses, not previously identified in birds.*** Of the three H5 viruses, H5N2 viruses have been most commonly detected in U.S. birds since December 2014. Of the 164 people with exposures, 64 people were exposed to wild birds, 13 were exposed to captive wild birds, 25 were exposed to poultry on backyard farm(s), and 62 were exposed to poultry on commercial farm(s). More than 48 million domestic birds have been affected with H5 bird flu.

Human infections with bird flu viruses are rare but have occurred in the past, most notably with H5N1*** and H7N9 viruses in Asia. Both of these viruses have resulted in sporadic human infections and deaths, most often following prolonged close contact with infected birds. The fact that none of the 164 people followed in the Emerging Infectious Diseases paper were infected is reassuring information. The report does note, however, that exposures in the United States are likely to be different from those in Asia and Africa where socio- and economic factors result in more prolonged, close exposures to birds without the use of PPE.

While the risk of human infection with these viruses is considered low at this time, CDC still considers it possible that these viruses may cause human infection resulting in severe disease. CDC recommends that people avoid close or prolonged contact with sick or dead infected poultry and their environments, and that personal protective equipment (PPE) be used when contact cannot be avoided. On June 2, 2015, the agency issued a health alert network advisory which summarized CDC recommendations to protect human health in the context of these domestic H5 bird flu outbreaks.

Investigation Details

For this investigation, CDC, USDA, the US Department of Interior worked with state health and agriculture departments in Arkansas, California, Idaho, Kansas, Minnesota, Missouri, Oregon, South Dakota, Utah, Washington, and Wyoming to gather H5 exposure information from outbreak areas. Laboratory tests were performed on specimens from patients who were exposed to H5 infected birds and later developed acute respiratory infection (ARI). People involved in flock depopulation were considered separately because of their instruction to wear PPE.

During the investigation, CDC received detailed information describing the exposures of 60 people which revealed that (44) 73% had exposure to infected birds while not wearing PPE while engaging in activities such as removing dead birds, collecting eggs, cleaning coops, or feeding birds. Five of 164 people developed ARI within 10 days after their last exposure. Four of five people tested negative for influenza by reverse transcriptase-polymerase chain reaction (RT-PCR) and one person had H3N2 seasonal influenza and no evidence of HPAI H5 virus infection. In addition to the 164 exposed people, zero of 29 persons involved in depopulation activities of infected flocks reported ARI within the 10 days of their last contact with infected birds.

Human infection with avian influenza may result from direct exposures like touching infected poultry or poultry parts, and butchering infected poultry or via activities (e.g., feeding poultry and/or cleaning poultry barns) which cause people to come into close proximity to infected birds or their environment.

For more CDC recommendations, please visit the CDC avian flu website, or call (800)-CDC-INFO [(800) 232-4636].

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*The HPAI H5N8 viruses detected in the United States are similar to viruses that were first reported on duck farms in China in 2009-2010. During 2014, similar HPAI H5N8 viruses were found in wild birds and poultry in Korea and Japan. In November 2014, HPAI H5N8 in poultry and wild birds was reported in England, the Netherlands, Germany and Italy. No human cases have been associated with these HPAI H5N8 viruses.

**The HPAI H5N2 viruses detected in the United States are similar to HPAI H5N2 viruses first detected in early December 2014 on poultry farms in British Columbia province, Canada. This is a reassortant virus that combines genes from Eurasian H5 viruses and North American N2 viruses. No human cases have been associated with either the North American or the Eurasian lineages of HPAI H5N2 viruses.

***The HPAI H5N1 virus detected in the United States is a reassortant virus with genes from HPAI H5 Asian viruses and low pathogenic North American viruses. It is different from the H5N1 Eurasian virus that has been associated with human illnesses, including severe disease and death.