麻豆传媒

The U.S. has reported its first severe case of H5N1 bird flu requiring hospitalization, the CDC announced.

The patient, in Louisiana, had exposure to sick and dead birds in a backyard flock, according to CDC, which confirmed the case on Dec. 13. The agency said it's the first case of H5N1 linked to a backyard flock in the U.S.

The patient is in critical condition, has underlying medical conditions, and is over age 65, a spokesperson for the Louisiana Department of Health told 麻豆传媒 in an email.

"The demonstrated potential for this virus to cause severe illness in people continues to highlight the importance of the joint coordinated U.S. federal response, the One Health response, to address the current animal outbreaks in dairy cows and poultry and limit the potential transmission of this virus to humans through animal contact," said Demetre Daskalakis, MD, MPH, director of CDC's National Center for Immunization and Respiratory Diseases, during a press briefing on Wednesday.

Daskalakis said that although a patient in Missouri who was hospitalized earlier this year had H5N1, that was not considered a severe case. The source of that patient's infection remains unknown.

Further analysis of the virus from the patient in Louisiana revealed that it belongs to the D1.1 genotype that has been detected primarily in wild birds, but also in some poultry flocks in the U.S.

The D1.1 genotype was involved in the severe case of H5N1 bird flu seen in a teenager in British Columbia, Canada, last month. The source of that patient's infection also remains unknown.

Many human infections in the U.S. have involved a different H5N1 genotype, B3.13, which has mainly been observed in dairy cows, but also in some poultry outbreaks in the U.S.

Daskalakis said genetic analysis is ongoing by the CDC to determine if there are any concerning changes in the virus, including changes that would signal an increased ability to infect humans, to be transmitted person-to-person, or that would make currently available diagnostics, antivirals, or candidate vaccines less effective.

No human-to-human transmission has been detected in the Louisiana case, Daskalakis said, adding that the risk to the general population remains low at this time.

To date, there have been 61 human cases of H5N1 bird flu across nine states in the U.S., Daskalakis said.

Last week, in routine influenza surveillance, Delaware identified a patient who was presumptively positive for H5N1, Daskalakis said. However, the CDC was not able to confirm H5N1 infection, and no known animal exposure was identified, so the case was reported as a probable H5N1 case, he said.

Also last week, a child in California may have developed H5N1 after drinking raw milk, but the CDC wasn't able to confirm the case.

During the press briefing, Eric Deeble, deputy under secretary for marketing and regulatory programs at the U.S. Department of Agriculture (USDA), said a new federal order requires that raw, unpasteurized milk samples be collected and provided to the USDA upon request. It also mandates that private labs and state veterinarians report positive H5N1 results to the USDA, and requires herd owners with positive herds to provide epidemiological information to the USDA.

Deeble said the agency has also approved seven vaccine field safety trials for bovine vaccine candidates, and one is currently moving forward. It's still early in the development process, he added, and it's difficult to predict how long development might take.

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