A new scoping review from CDC researchers found that “asymptomatic avian human influenza A(H5N1) infections occur, and person-to-person transmission is likely in some settings.” CIDRAP has the news.
Over 1,000 A(H5N1) infections among humans have been reported globally since 1997. The team sought to determine which of those cases, if any, involved asymptomatic individuals. They found 10 reports of 18 asymptomatic infections. Two of the cases were confirmed with molecular and serologic methods – “one patient was also exposed to infected chickens, and the other is believed to have been infected through human-to-human spread, because they had no contact with sick or dead poultry.”
The authors of the study noted that most of the asymptomatic cases were “identified through enhanced surveillance or household contact investigations of persons with known exposure.” They urge that “robust data collection is needed from persons with possible asymptomatic A(H5N1) virus infection to inform future public health responses.”
A related commentary noted that “high viral levels have been found [in the U.S.] in raw milk, and live virus has been detected in mammary tissue and milking equipment.” The authors also wrote that this study’s findings “challenge the traditional perception that human H5N1 infections are almost always symptomatic and severe and that no human-to-human H5N1 spread has occurred.” These findings “underscore the importance of carefully examining clusters where limited transmission may occur.”
