Two Human H5N1 Cases Yesterday - Good News, Bad News, or Both?

Improved testing does not equal greater risk; however, H1N1 remains uncomfortably infectious for human contacts, requiring intense monitoring for onward spread and potential genomic changes

Headlines for human H5N1 infections moved from Missouri to California yesterday, as the California Department of Public Health announced 2 confirmed (unrelated) cases of H5N1 infections in dairy farm workers: UPDATE: CDPH Confirms Two Cases of Bird Flu in California. CDC followed with a news release of their own: CDC Confirms New Human Cases of H5 Bird Flu in California | CDC Newsroom

Both cases apparently involved conjunctivitis as the primary complaint with little or no respiratory involvement, similar to an early case from Texas pictured here:

Both cases were apparently mild and not hospitalized; this has been the common scenario with conjunctival H5N1 infections. The human conjunctiva contains appropriate alpha 2,3 sialic acid receptors for H5N1 viral attachment, making these infections a risk for individuals with inadequate eye protection in close contact with infected environments.

Anecdotally, observers have widely reported that these infections (both conjunctival and some respiratory) are very common and undiagnosed on infected dairy farms. Thus, the number positive samples in a day or week during a large outbreak like in California are really just a function of how effectively workers are being screened. Recall that in Colorado last summer, multiple cases were found in poultry depopulation workers when medical staff was on site to monitor and swab symptomatic cases.

Regardless of case numbers each case is still each important on its own, because any one of them could signal trends towards viral adaptation for human-to-human spread. Quality of case follow-up is just as important as number of cases positive. Sequencing is critical, as is checking for any evidence of onward spread to human (or animal) contacts.

In summary, these 2 cases are not by themselves a cause for increased concern for pandemic risk. It’s good news that California has been able to secure cooperation in testing a least a few symptomatic workers. With all the infected herds in the state, I’d expect that they might find many more cases if their public health outreach remains successful.

It’s also good news that CDC is sequencing the 2 isolates. If successful, they will likely obtain matching dairy samples from farms where the workers are employed for comparison. That is especially good news for animal researchers because it will provide accelerated complete genome results to the public from CDC for 2 herds in California which would not otherwise be available in a timely manner from NVSL. It will be interesting to learn of experts’ analyses of the latest sequences from California, given recent perceptions of a more lethal clinical disease course in cows.

Finally, the proof for increased risk for pandemic potential remains in closely monitoring for human-to-human spread. That is why CDC is so active in developing robust serological methodology now, so that they can better assess infections in contacts. Contacts may not test positive for the virus but can still be evaluated serologically for evidence of response to viral exposure. As more human cases are identified, follow-up testing of contacts will become a more time-consuming task, testing our public health infrastructure.

I came an interesting article this morning regarding the 2024 election that is strictly apolitical! The writer states that the 2024 winner will be labelled the “Bird Flu President”, because this situation is brewing to be a major 2025 issue for whoever wins the election. Neither party wants to address it right now, because it’s a no-win issue for voters. However, we would all be well-advised to keep pandemic risk and response in mind as we make our individual candidate choices on November 5th:

The Atlantic -The Bird-Flu President

John

P.S. SOMEONE, please be thinking of a better popular press name for “bird flu”, a horrible name for a multi-species influenza threat. Its popular use is ubiquitous and will need repeated educational efforts to improve.