Avian Flu Diary: A Review of Significant HPAI H5 Related Events Over The Past 3 Weeks

CDC Case Count 11/10/24

#18,406

While it may not tell us where HPAI H5 will go in the days and weeks ahead, the events of the past 21 days have demonstrated how quickly the status quo with avian flu can change.

On October 21st, the CDC counted 27 human H5 infections in the United States in 2024.

Three weeks later that number is officially 46 (a gain of 19), but this doesn't include 4 cases confirmed by states (California & Washington) but not the CDC, a 2nd (strongly suspected) case in Missouri, or any of the 8 cases turned up last week by retrospective serology tests.

Three weeks ago, both the United States and Canada had gone months without substantial outbreaks in poultry, but between them have since reported > 40 outbreaks.

At the same time the known number of American dairy herds infected by H5N1 has increased by 46% (from 324 to 473), across (now) 15 states.

All of that by itself would be concerning, but this doesn't begin to scratch the surface of H5 related events of the past 3 weeks. With that in mind, a mini review of 10 other H5 avian flu related events or revelations from the past 21 days.

Starting with the oldest, on October 21st the state of Washington announced their First Presumed Human Infections with H5 (n=4), in exposed poultry cullers. We learned that this outbreak was due to a new genotype D1.1, and as of today, they are reporting 14 human cases.

On October 24th, we got the long awaited Serology Results On Missouri H5 Patient's Contacts, which found no evidence of transmission to HCWs, but did strongly suggest a housemate was infected at the same time as the index case. The source of these infections has yet to be identified.

On October 28th, in Nature: A Human Isolate of Bovine H5N1 is Transmissible and Lethal in Animal Models, we learned that the first Texas H5 isolate could be transmitted through the air between separated ferrets, that it might be capable of binding to and replicating in human respiratory tract cells, and that oseltamivir (Tamiflu) might not be as effective in treating it as Baloxivir.

On October 30th, the USDA Reported the 1st Detection of HPAI H5N1 in Swine (Oregon), once again with another new genotype D1.2, which had infected poultry on the same farm. A week later (Nov 7th) the USDA Confirmed a 2nd Pig on Oregon Farm Tested Positive.

On October 31st, Utah Became the 15th State To Report HPAI H5N1 In Cattle (n=8) a little more than two weeks after an outbreak of the B3.13 `bovine' genotype was detected in a large poultry operation in Cache County. The number of infected herds was last reported to be 13.

On Nov 2nd the CDC Updated their Results On Texas H5N1 Virus In Ferrets, reporting that the virus transmitted in ferrets more efficiently than initially reported, and warning that `The results suggest this virus has the potential to cause severe illness in people'.

On Nov 3rd, the Los Angeles County Health Dept. issued a Statement on H5 Avian Flu Detected In Wastewater, and while an animal source is suspected, human infections could not be ruled out.

On Nov 7th, in MMWR: Serologic Evidence of Recent Infection with HPAI A(H5) Virus Among Dairy Workers we learned that 7% of (115) farmworkers tested positive for antibodies for H5, although half of them reported remembering no illness, and the other half only mild complaints. An early study had found no evidence of sub-clinical infection.

That MMWR study prompted a major release of revised guidance by the CDC on Nov 8th, calling for - among other things - expanded testing of exposed, but asymptomatic, individuals.