California reports 6th human case of H5N1 bird flu

Health officials in California have reported another human case of H5N1 bird flu, taking the total number of dairy farm workers who have been infected during the past week to six. All of the cases were caused by animal-to-human transmission.

All six cases so far have been found in individuals who worked at dairy farms in the Central Valley, suggesting none of them were caused by human-to-human transmission, according to the California Department of Public Health (CDPH).

Of the six cases, four have been confirmed by the Centers for Disease Control and Prevention (CDC). The other two have tested positive in California and are awaiting final confirmation from the CDC.

“All cases so far have experienced mild symptoms, including eye redness or discharge (conjunctivitis),” CDPH said in a statement on Thursday. “None of the individuals have been hospitalized.”

The statement added: “While the risk to the general public remains low, additional human cases of bird flu are expected to be identified and confirmed in California among individuals who have contact with infected dairy cattle. CDPH continues to work closely with local health jurisdictions to identify, track, test, confirm, and treat possible and confirmed human cases of bird flu.”

Based on CDC’s genomic sequencing of California’s first two human bird flu cases, there is no evidence to suggest an increased ability for the virus to infect or spread between people and no known reduced susceptibility to antiviral medications.

Pasteurized milk and dairy products continue to be safe to consume, as pasteurization is fully effective at inactivating the bird flu virus, according to CDPH. As an added precaution, and according to longstanding state and federal requirements, milk from sick cows is not permitted in the public milk supply.

LINK: A list of all human cases of H5N1 bird flu since 2021

A newer strain of H5N1, clade 2.3.4.4b, has raised concern due to its global spread and the growing number of cases in mammals, including outbreaks among dairy cows in the U.S. Only a limited number of human cases have been reported so far after contact with infected birds or cows.

Earlier on Thursday, officials confirmed that H5N1 bird flu has so far been found at 99 dairies across California, the nation’s largest producer of dairy. That’s up from 44 earlier this month.

33 human cases of H5N1 bird flu have been reported so far this year, including 20 in the U.S., 10 in Cambodia and one each in Australia, Vietnam and China. Only the U.S. cases – 10 in Colorado, 6 in California, 2 in Michigan and one each in Texas and Missouri – were caused by the newer variant, clade 2.3.4.4b.

Last month, a patient in Missouri tested positive for H5N1 bird flu despite having no known links to infected animals. The patient was hospitalized but has since recovered. The source of the infection is still unknown but no other cases have been reported.