For months, as human cases of the H5N1 bird flu, linked to an outbreak of the virus in U.S. dairy cattle, mounted, one question loomed larger than others: How many human infections are being missed?
Farmworkers face the most intense exposure to the bird flu virus, but resistance from farmers and a lack of health insurance and paid sick leave in the industry have limited testing of workers and limited public health officials’ ability to track where infections have occurred. virus may be spreading. Now, the long-awaited results of blood tests conducted by the Centers for Disease Control and Prevention are starting to fill the picture.
The findingspublished Thursday, suggests that a small but not insignificant number of H5N1 infections are going undetected among people who work with dairy cows. Blood samples taken from 115 farmworkers in Michigan and Colorado this summer found evidence of recent infection in eight people — half of whom remembered being sick around the same time the cows were sick. The other half could not remember having any complaints.
The tests are known as serological studies and involve looking out for antibodies in the blood: molecules made by the immune system in response to a pathogen’s attack and that persist long after the infection. Finding it is a signal of previous contact with a particular virus and helps scientists understand how widely it has spread.
While the new results suggest that current public health efforts are missing cases, they do not indicate that the H5N1 strain linked to the dairy cattle outbreak has acquired the ability to spread from person to person.
“There is nothing that we have seen in the new serology data that raises concerns about person-to-person transmission,” Nirav Shah, the agency’s deputy director, said at a news conference Thursday morning.
The agency believes the virus still poses a low risk to the general public.
So far this year, 45 people have been infected with H5N1 due to exposure to livestock or poultry, with one additional case from an unknown source. CDC officials said the newly discovered infections would not be added to the list of confirmed cases. But the study gives new urgency to reports of undiagnosed conditions among farm workers and veterinarians.
In response to the new data, the CDC now recommends that all farmworkers exposed to infected animals be tested for H5N1, regardless of whether they have symptoms or not. Previously, the agency recommended that only individuals who had been exposed and were showing symptoms should be tested.
The aim of this expansion is to intensify case detection efforts so that even workers with mild or unnoticeable infections can be offered treatment and isolation. The CDC also recommends that Tamiflu be offered to all individuals on a farm with infected animals who have had a high-risk exposure – such as being splashed with milk from a dairy cow or participating in a culling operation on a poultry farm – without adequate personal protective equipment.
The CDC study found that all eight people with H5N1 antibodies had reported cleaning milking parlors, and most reported milking cows. None reported wearing respiratory protection and less than half wore eye protection. Other research has shown that H5N1 appears to primarily infect the mammary glands; the amount of virus in the udders of infected cows is very high, and the virus can survive for hours on surfaces and milking machines, leaving little doubt that there is a lot of spread. happens in milking parlors.
Although human cases have been mild so far, public health officials worry that when infected, the virus has a greater chance of picking up mutations that could make it more dangerous.
“Simply put, the less space we give this virus, the less opportunity it has to cause harm,” Shah said. “The best way to do that is to identify, treat and isolate as many human cases as possible as quickly as possible.”
However, it remains unclear what impact these new recommendations will have in reducing the H5N1 outbreak, given the realities on the front lines and the CDC’s lack of legal authority to order cooperation. Many farmers are reluctant to let public health officials conduct on-site testing and have resisted the offer of free personal protective equipment for workers. In many cases, environmental conditions make PPE virtually useless in dairies – extreme heat waves in California this summer not only resulted in more severe illness among animals, but made wearing masks and goggles too hot or even dangerous for workers.
Although Tamiflu is effective at reducing the amount of virus in a person’s body, thereby lowering the risk of onward transmission and the chance of the virus mutating, it works best if given as early as possible, within 48 hours after the onset of symptoms. . Filling a prescription within that time frame can be a challenge for farmworkers, who often live in remote places and may lack transportation to reach medical care.
Public health authorities in states like Michigan and Colorado have been especially successful in reaching farmers, allowing them to conduct these types of studies in collaboration with the CDC. Other states, such as California, where nearly half of confirmed human cases have been reported in recent weeks, have not yet indicated whether they will conduct their own serological testing.
The CDC said it continues to try to learn more about the extent to which H5N1 has caused undetected infections among people who work closely with cows in any way. In September, about 150 veterinarians at the American Association of Bovine Practitioners’ annual conference in Columbus, Ohio, provided blood samples to be tested for evidence of H5N1 antibodies.