A second human case of bird flu infection linked to the current H5N1 outbreak in dairy cows has been detected, in a farm worker who had exposure to infected cows, Michigan state health authorities announced on Wednesday.
In a statement, health officials said the individual had mild symptoms and has recovered. Evidence to date suggests this is a sporadic infection, with no signs of ongoing spread, the statement said.
“Farmworkers who have been exposed to impacted animals have been asked to report even mild symptoms, and testing for the virus has been made available,” Natasha Bagdasarian, the state’s chief medical executive, said in the statement.
“The current health risk to the general public remains low,” she added. “This virus is being closely monitored, and we have not seen signs of sustained human-to-human transmission at this point. This is exactly how public health is meant to work, in early detection and monitoring of new and emerging illnesses.”
This is only the third human case ever of H5N1 reported in the United States. A man in Texas who worked on a dairy farm was infected there earlier in this outbreak. The country’s first case, in the spring of 2022, was in a man in Colorado who was involved in culling H5N1-infected birds in a poultry outbreak there.
The Centers for Disease Control and Prevention said a nasal swab taken from the Michigan farm worker was negative for flu. But a swab of the person’s eye was sent to the CDC, where it tested positive for H5 flu virus, though final confirmation that it’s the H5N1 subtype is pending genetic sequencing. This was the only symptom the individual had, the CDC said.
In the Texas case in late March, the only symptom reported was conjunctivitis, also known as pink eye.
“We found this case because we were looking for this case. And we were looking for it because we were prepared. And in particular, the state of Michigan was prepared,” CDC’s Principal Deputy Director Nirav Shah said during a press conference organized by the U.S. Department of Health and Human Services.
Jennifer Nuzzo, director of the Pandemic Center at Brown University’s School of Public Health, said she wished other states were looking for H5N1 cases as aggressively as Michigan is.
“If there’s any takeaway from this finding it’s that this is probably the tip of the iceberg because this is the one state that we know of that has done the most in terms of testing on farms of both cows and also monitoring workers that are on the farms where they found cattle infections,” she told STAT.
Nuzzo said she took no comfort from the fact that only two human cases have been detected so far in this outbreak, and worries that people may be reading too much into that low number.
“The absence of finding cases is being interpreted as reassuring, that this [outbreak] is perhaps something that is abating,” she said. “And I have absolutely no ability to tell you that’s happening, in part because I think the testing that we’re doing could very well be qualitatively … misleading.”
During the press conference, Dawn O’Connell, assistant secretary for preparedness and response at HHS, revealed that 4.8 million doses of H5N1 vaccine that has been stockpiled in bulk is in the process of being put into vials — a process called fill and finish. This is a little less than half of the vaccine believed to be effective against the current strain of H5N1 that is stored in the National Pre-Pandemic Influenza Vaccine Stockpile.
O’Connell said the decision to make the vaccine more readily deployable was taken a couple of weeks ago. “It takes a couple of months to be able to fill and finish vaccine doses… so I thought it made sense, given what we were seeing,” she said.
O’Connell said a decision to use the vaccine has not been made.
To date, nearly 900 people in 24 countries have been confirmed to have been infected with H5N1 since 2003, with most cases tied to exposure to infected poultry. On rare occasions, there have been small clusters of cases that raised questions about whether limited person-to-person spread has occurred — something that is hard to prove when multiple people have the same exposures to infected animals. Ongoing spread among people has not been detected, and it is believed the virus would need to evolve further to gain the ability to spread easily to and among people.
The outbreak in cattle, the first known to have occurred with this virus, was confirmed in late March, though evidence suggests that it had been underway for several months before testing revealed the cause of a drop in milk production among cows.
Since then the U.S. Department of Agriculture has confirmed outbreaks in 52 herds in nine states, including Michigan, which has reported 19 infected herds — more than any other state. (The USDA’s most recent tally does not include four that Michigan reported since May 17.)
Experts following the outbreak believe the national count of affected herds significantly underestimates the scope of the problem. Both the USDA and the CDC have admitted that farmers have been reluctant to allow testing of their cows or their workers, afraid of the stigma attached to being associated with the outbreak.
But that has been less true in Michigan, where state officials have taken a uniquely aggressive stance in its public health response, informed, in part, by the devastating impacts H5N1 has had on the state’s poultry flocks in the past few years.
On May 1, Tim Boring, director of the state’s Department of Agriculture, declared an “extraordinary animal health emergency,” signing an order requiring Michigan farmers to step up their biosecurity measures. “Most farms have been good cooperators with that,” Boring told STAT in an interview last week.
Farmers have also been open to working with local health authorities to fill out questionnaires that could help investigators track how the virus is moving between dairy herds throughout the state. “Hundreds and hundreds of farm workers here in Michigan have been interviewed,” Boring said. “They understand the importance of understanding how this is moving around so we can limit the spread of this.”
Local health authorities have also been monitoring workers from farms with infected herds for symptoms — either through regular phone calls with farm supervisors or automated text messages that ask if they’ve been experiencing conjunctivitis or any flu-like symptoms, even mild ones. Testing is being offered to any symptomatic workers who’ve been exposed to animals on affected farms or are living in congregate settings with people who’ve been exposed.
In an interview Wednesday afternoon, Bagdasarian, the Michigan health official, described the discovery of a human case as a sign these efforts to find new infections are paying off. “Michigan has really been one of the states leading in terms of testing, so it’s not surprising that we have picked up on this sporadic case,” she said. At least 35 people have been tested so far, she said. This case is the first to have come back positive.
Bagdasarian said officials have seen no evidence of secondary infections. But the state is not yet conducting serological surveys — looking for antibodies to H5N1 in the blood of farm workers and those they’ve been in contact with — to determine if there have been unreported cases, and possibly even spread from those individuals to others.
“We’ve always talked about the need to do additional studies to do additional engagement, and to do a big look at serology, especially for people who may have remained asymptomatic throughout,” Bagdasarian said. “That would be a next step.”
Shah said the CDC would very much like to conduct serology studies among dairy farm workers, including those, like the Michigan individual, who test positive. “At this time, we’re not there yet,” he said.
Eric Deeble, the USDA’s acting senior advisor for H5N1, announced during the news conference that additional financial incentives are being planned to try to entice dairy farmers to report infections in their herds and take steps to reduce the risks to cows and workers on the farms. Compensation for lost milk — a substantial drop in milk production is the most notable sign of infection in a herd — is planned, but will take a few more weeks to finalize, he said.
This story has been updated throughout with comments from the HHS news conference and interviews with Bagdasarian and Nuzzo.