No cases of H5N1 avian influenza have been identified among farmworkers, according to the Centers for Disease Control and Prevention (CDC).

For several months, since human cases bird flu H5N1 With a virus outbreak among U.S. dairy cattle, one question has become more important than others: How many human infections go undetected?

Agricultural workers are most exposed to the avian influenza virus, but resistance from farmers, as well as the lack of health insurance and paid sick leave in the industry, limit the amount of testing of workers and hampered public health officials’ ability to track where the virus can spread. Now, long-awaited blood test results from the Centers for Disease Control and Prevention are beginning to fill in the picture.

Conclusionspublished Thursday suggest that a small but significant number of H5N1 infections go undetected among people who work with dairy cows. Blood samples taken over the summer from 115 farmworkers in Michigan and Colorado found evidence of recent infection in eight people, half of whom recalled getting sick around the same time as the cows. The other half could not remember any symptoms.

These tests, known as serological tests, involve detecting antibodies in the blood – molecules produced by the immune system in response to a pathogen attack that persist long after the infection has passed. Their detection signals past exposure to a particular virus and helps scientists understand how widely it has spread.

While the new findings show that current public health efforts are missing cases, they do not indicate that the H5N1 strain associated with the dairy cattle outbreak has acquired the ability to spread from person to person.

“We haven’t seen anything in the new serological data that raises concerns about human-to-human transmission of the virus,” Nirav Shah, the agency’s principal deputy director, said at a news conference Thursday morning.

The agency believes the virus continues to pose a low risk to the public.

This year, 45 people have been infected with H5N1 through contact with cattle or poultry. another case with an unknown source. CDC officials said newly identified infections will not be added to the list of confirmed cases. But the study brings new urgency to reports of undetected illnesses among farmworkers and veterinarians.

In response to the new data, the CDC now recommends that all farm workers exposed to infected animals get tested for H5N1, regardless of whether they have symptoms. Previously, the agency recommended testing only those who had been exposed and had symptoms.

The goal of this expansion is to increase case-finding efforts so that even workers with mild or undetectable infections can be offered treatment and isolation. The Centers for Disease Control and Prevention (CDC) also recommends offering Tamiflu to anyone on farms with infected animals who have been exposed to a high risk (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 reported cleaning milking parlors, and most reported milking cows. None reported wearing respiratory protection, and less than half wore safety glasses. Other studies have shown that H5N1 appears to primarily attack the mammary glands – the amount of virus in the udders of infected cows is very high, and it can remain alive on surfaces and milking machines for several hours, leaving no doubt that significant spread of the virus is occurring in milking parlors. .

Although human cases have so far been mild, Public health officials are concerned that during infections, the virus has more opportunities to acquire mutations that can make it more dangerous.

“Simply put, the less room we give this virus to spread, the less likely it is to cause harm or damage,” Shah said. “The best way to do this is to identify, treat and isolate as many human cases as quickly as possible.”

However, it remains unclear what impact these new recommendations will have on containing 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 allow public health officials to conduct on-site testing and pushed back against proposals for free personal protective equipment for workers. In many cases, environmental conditions make personal protective equipment virtually unsuitable for use in dairies—extreme heat in California this summer not only led to more severe illness among animals, but also made wearing masks and goggles too hot or even dangerous for workers.

Although Tamiflu is effective in reducing the amount of virus in a person’s body and therefore reducing the risk of any further transmission and the chance of the virus mutating, it works best if given as early as possible, within 48 hours of the onset of symptoms. . Getting a prescription within this time frame can be challenging for farmworkers, who often live in remote locations and may not have transportation to get to medical care.

Public health authorities in states like Michigan and Colorado have been particularly good at this. invade farmersletting them conduct similar studies in collaboration with the CDC. Other states, such as California, where nearly half of the confirmed human cases have been reported in the past few weeks, have not yet said whether they will conduct their own serology surveys.

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 possible. In September, at the American Association of Cattle Practitioners’ annual conference in Columbus, Ohio, about 150 veterinarians provided blood samples to be tested for H5N1 antibodies.