Avian flu case without known animal contact

Latest news from H5N1

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What’s new: There’s an old saying in epidemiology that outbreaks always happen at 5 p.m. on a Friday. Those refrains often exist because they contain a kernel of truth.

This afternoon, the Missouri Department of Health (MDH) reported a case of avian influenza A (H5) in a person who was hospitalized in August. The specific flu subtype was not identified at the time of hospitalization, but additional testing revealed it to be the same subtype as what has caused outbreaks in wild birds, farmed poultry and dairy cattle¹.

What’s notable is that the person did not report exposure to animals. There have been a handful of human cases of H5N1 reported, but all had direct contact with infected dairy herds, poultry flocks, or other known exposures.

Caveats: MDH notes, “The specimen was forwarded to CDC for additional testing and was confirmed as H5 subtype of flu, also known as a bird flu, or avian flu. Additional virus characterization is underway at CDC.” It’s also worth noting that the press release did not specify that the person was hospitalized because of influenza infection, or whether it was picked up incidentally. We also don’t know if it’s the same clade as what has been affecting herds.

My take: It’s not great news, but nor is it seismic at this point.

The person’s hospitalization (if it was, in fact, due to flu) is worrying, as severe outcomes are more alarming than mild illness.

The lack of animal exposure is also concerning, as it suggests the infection could have come from another person, indicating possible human-to-human transmission (which would be highly alarming), or from an unnoticed animal source. I am sure that MDH is investigating to learn more about the source of the infection. Both backward and forward contact tracing is important, to look for evidence of human-to-human transmission. But until such data is collected and analyzed, my level of alarm is only mildly heightened.

I am encouraged that this case was detected through existing surveillance systems, which bodes well for our ability to identify any additional cases in the future. Federal, state and local health officials maintained flu surveillance through the summer months in response to the H5 situation, and that was definitely the right move.

That said, I have long worried about H5N1. I’ve written so in Foreign Affairs, and my team at Johns Hopkins has developed a frequently-updated risk assessment to analyze possible future scenarios. With continued evidence of human infections, both linked and unlinked to known sources of the virus, we should continue intensified disease surveillance to track how and where these infections are occurring.

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1. Edited to add: The virus has been confirmed as H5, but further genomic characterization to determine whether it is the same clade as the current outbreak in dairy cattle is still underway. Other clades are circulating, including one that has caused a number of human cases in Cambodia.