#18,398
The CDC has updated their human case count of confirmed H5 infections (n=46), adding 4 more cases since Monday's update. These CDC counts are - at best - fleeting snapshots in time, since the number of cases continues to rise and they don't necessarily match what the individual states are reporting.
Washington State has reported 14 human cases, but only 11 have been confirmed by the CDC.
Similarly, California is reporting 1 more locally confirmed case than the CDC is reporting, since the CDC was unable to verify those results. There are also likely additional cases in the pipeline, waiting to be confirmed.
Testing of exposed farm workers has been generally limited to symptomatic individuals. The CDC justifies this decision by citing a recent (small) seroprevalence study in Michigan, which tested 35 farm workers and found no neutralizing or HI antibodies specific to avian influenza A(H5N1) virus.And then there are the anecdotal reports of symptomatic farm workers in several states which were never tested for the virus. How many of those might have contracted HPAI H5 is unknown.
That said, we've seen a number of seroprevalence studies on (various) HPAI H5N1 strains over the years that have found limited evidence of asymptomatic (or very mild) infection with H5 avian influenza.
While these official updates are important in showing us trends, they can't tell us the true number of cases. We can say `at least' 46 cases, but it would not be surprising if this was the proverbial `tip of the iceberg’ or in the case of the CDC graphic below, the `top of the pyramid’.
What we can say is:
- for the first two years of circulation of HPAI H5 in the United States (2022-2023) only 1 probable human infection was reported.
- The first human infection of 2024 was reported in late March, and over the next 6 months (through Oct 1st), 14 human cases were reported.
- Over the past 5 weeks, that number has more than tripled, to at least 46 cases.
