New human cases of avian flu have been reported—this time, in California and Washington, as well as in Missouri. As of November 1, 2024, the latest reported cases have increased the total number of avian flu human cases in the United States this year to 41.
Reports on the Californian cases have been released throughout the month of October by the Centers for Disease Control and Prevention (CDC). As of November 1, 17 human cases of avian flu have been reported there.
The first six cases of avian flu in California reportedly occurred in dairy workers on different farms, with the exception of two cases from a single farm. These two cases worked on different parts of the farm and were not close contacts of each other.
As of October 28, avian flu has been confirmed in 203 dairies in California, according to the California Department of Food and Agriculture (CDFA). Of 16 confirmed human cases of bird flu in California, the CDFA noted that those cases have had mild symptoms, including conjunctivitis; none have required hospitalization.
The CDC noted in a recent report that genetic sequencing on samples from nine of the confirmed California cases showed that the viruses were closely related to H5N1 viruses detected in infected dairy cattle. Testing of other cases continues.
In addition to the California cases, the CDC has confirmed nine cases of avian flu in poultry workers in Washington state. The affected cases had signs of mild illness, some with upper respiratory illness, and many with conjunctivitis or pink eye; none have required hospitalization. Genetic testing of specimens from these human cases are underway.
In other news, a human case of H5N1 was reported in Missouri in early September. Serological testing (testing of blood serum) of the contacts of this Missouri case showed that six healthcare workers who fell ill after having contact with this case did not have avian flu. However, the CDC reported in late October that serology testing of the household contact of that case has shown evidence of exposure to H5N1. Neither of these confirmed cases in Missouri had exposure to infected animals. Because the two people from the same household had symptoms starting at the same time, this suggests there was a single common exposure to bird flu rather than person-to-person transmission.
As of October 31, 403 dairy herds have been affected by H5N1 across 14 states; H5N1 has been detected in 1,182 flocks in 48 states, including 518 commercial flocks and 674 backyard flocks.
Although the CDC still considers the overall public health risk from H5N1 to be low, people who work on farms are considered to be at higher risk. In response, the CDC has allocated more than 100,000 doses of seasonal influenza vaccine to 12 affected states to provide to farm workers. While the seasonal flu shot does not protect against H5N1 directly, it can prevent co-infection with seasonal flu and help reduce the burden on rural healthcare systems. The CDC is also piloting a program with pharmacy partners in California and one other state to provide free flu testing and triage for farm and dairy workers.
The CDC continually updates its website with information on new and existing cases of avian flu. Stay informed of the latest updates from the CDC.
Read background information about the avian flu currently in circulation
