A case of H5 influenza, also known as avian influenza or bird flu, has been reported in a farm worker in Michigan who had regular exposure to infected livestock, according to the Michigan Department of Health and Human Services and the US Centers for Disease Control and Prevention.
It’s the second case reported as part of an ongoing outbreak of the virus in birds and cattle across the country and the third bird flu case ever reported in a person in the US. However, health officials emphasized Wednesday that the risk to the general public remains low.
The person was being monitored for the virus because of their exposure to infected cattle, the CDC said in a news release Wednesday. A nasal swab tested negative for influenza at the state health department and later at the CDC, but an eye swab tested positive. The person reported only eye symptoms, and they have recovered.
Eye symptoms such as redness, swelling and watering were also the only ones reported in the previous human case in this outbreak, in a dairy farm worker in Texas. That man took antiviral medications and recovered with no lasting problems.
“It is not unexpected that comprehensive testing identified a human infection,” the Michigan Department of Health and Human Services said in a news release Wednesday. “Information to date suggests this is a sporadic infection, with no associated ongoing spread person-to-person.”
The Michigan farm worker was one of about 170 people enrolled in an active monitoring program in which they received a text message from the state health department each day that asks about potential symptoms. When the person indicated the presence of symptoms, public health workers took samples, offered antiviral medications to them and their close contacts, and urged them to isolate.
The CDC received the samples on Tuesday and reported the test results to Michigan health officials that night, said Dr. Nirav Shah, principal deputy director of the CDC.
“This case was not unexpected,” Shah said Wednesday, emphasizing the agency’s ongoing efforts to help farms prepare for the spread of the virus. “It does not change our assessment of the risk overall. What it does do, however, is it reinforces the message that CDC has been putting out since late March, which is that entities involved with this – be they local health departments, farms, farm workers and farm worker organizations – ought to be alert but not alarmed by these developments.
“We have not seen evidence of other cases in this area or elsewhere in any of our monitoring systems, let alone any evidence of human-to-human transmission,” he said. “And this is reassuring, but the work of public health is not done. In the coming days, we’ll have additional information on the genomic sequence or the DNA fingerprint of this particular virus. And we’ll be able to compare it to the virus from infected cows in Michigan, as well as to compare it to the virus from the earlier human case in Texas.”
The fact that the nasal specimen tested negative while the eye swab was positive is also, “in a sense, reassuring,” Shah said, as it indicates a reduced likelihood that the virus is spreading through respiration.
Although remnants of the virus have been found in samples of dairy products purchased from grocery stores, the US Food and Drug Administration “continues to affirm our assessment of the safety of the commercial milk supply,” Dr. Don Prater, acting director of the agency’s Center for Food Safety and Applied Nutrition, said Wednesday.
“To date, the totality of the evidence – including studies on the effectiveness of pasteurization against multiple pathogens, recent studies on the effectiveness of pasteurization of [highly pathogenic avian influenza] and eggs at lower temperatures than generally used in dairy products, and negative retail sample results to date – continue to indicate the commercial milk supply is safe. We also continue to strongly advise against the consumption of raw milk” or milk that has not been pasteurized.
Testing with a substitute virus in ground beef found some live virus in patties cooked to 120 degrees or rare, but it was present at “much, much reduced levels,” according to Eric Deeble, acting senior adviser for highly pathogenic avian influenza at the US Department of Agriculture, and it’s not clear whether it would be enough to make someone sick.
Correction: A previous version of this report misidentified the genetic strain of the virus.
