Even because it has turn out to be more and more clear that the fowl flu outbreak on the nation’s dairy farms started months earlier — and might be rather more widespread — than beforehand thought, federal authorities have emphasised that the virus poses little danger to people.

But there’s a group of people who find themselves at excessive danger for an infection: the estimated 100,000 women and men who work on these farms. There was no widespread testing to see what number of could also be contaminated. None have been vaccinated in opposition to fowl flu.

That leaves the employees and their households susceptible to a poorly tracked pathogen. And it poses broader public well being dangers. If the virus had been to search out its manner into the broader inhabitants, specialists say, dairy staff can be a probable route.

“We do not know if this virus goes to evolve to turn out to be a pandemic pressure, however we all know right now that farmworkers are being uncovered, and we’ve good causes to assume that they’re getting sick,” mentioned Jennifer Nuzzo, director of the Pandemic Middle at Brown College Faculty of Public Well being.

A majority of dairy farmworkers are Spanish-speaking immigrants, typically undocumented, who could not have paid sick go away or be protected by occupational security legal guidelines. They could lack entry to medical suppliers, and their employers will be illiberal of absences.

“This sector of staff will not be solely on the very, very highest danger as a result of they’re having that direct, intimate contact with discharge, uncooked milk, with contaminated animals, however they’re additionally on the very, very highest degree of danger by way of having no social security web,” mentioned Elizabeth Strater, an organizer with United Farm Staff.

Interviews with greater than three dozen federal and state officers, public well being specialists, farmers and staff’ organizations present how little is understood about what’s occurring on farms: what number of staff could also be affected, how the virus is evolving and the way it’s spreading amongst cows.

To this point, the virus, referred to as H5N1, has been detected in cattle herds in 9 states. Whereas veterinarians have mentioned there are unconfirmed reviews of farmworkers with flulike signs, solely 30 have been examined as of Wednesday.

Barring extraordinary circumstances, state and federal well being officers do not need the authority to demand entry to farms. As an alternative, the Meals and Drug Administration and the Division of Agriculture are testing milk and floor beef on grocery cabinets for the virus.

The Facilities for Illness Management and Prevention is ready for contaminated individuals to point out up at clinics.

“Do you wish to discover out a few virus when it’s spreading amongst individuals a lot that they’re coming into emergency rooms in hordes, or do you wish to catch it on the farms so you may deal with the individuals and gradual the unfold?” mentioned Rick Vivid, the chief government of Vivid World Well being, which focuses on responses to public well being emergencies.

A tangled regulatory system complicates the state of affairs, mentioned Dr. Jay Varma, who served within the C.D.C.’s food-borne illnesses department and oversaw meals security as a deputy commissioner at New York Metropolis’s well being division.

The agriculture division regulates massive industrial farms and may mandate testing of animals — though it has not but executed so — however not of farmworkers. The division “doesn’t ever wish to be able the place it has to declare that meals provide from the U.S. is unsafe, as a result of a few of these meals merchandise could also be exported to different nations and that may have an enormous financial impression,” Dr. Varma mentioned.

The C.D.C. has authority over ports of entry into the US, however domestically the company wants state approval to do a lot of its work. The F.D.A., Occupational Security and Well being Administration, the Environmental Safety Company and Citizenship and Immigration Providers all have roles to play, however every has its bureaucratic layers and institutional tradition.

This patchwork will be an obstacle throughout a illness outbreak, some specialists mentioned. In 2009, the response to a cluster of bacterial infections in a salami product was delayed as a result of the Division of Agriculture regulated the meat, the F.D.A. was liable for the cracked black pepper that coated it and the C.D.C. was in command of investigating the individuals who grew to become sick.

Dr. Nirav Shah, principal deputy director of the C.D.C., dismissed the notion that forms was an impediment as “overly simplistic,” and mentioned the businesses responding to the outbreak discuss quite a few instances a day to coordinate their actions and to work with state companions.

“These things is tough,” he mentioned. However “we’re working collectively on this as a result of we’ve widespread objectives.”

Due to the comparatively small variety of circumstances — 36 affected herds out of some 26,000 nationwide and one contaminated farmworker — some farmers see the fowl flu as a distant risk. Even those that help public well being efforts are hesitant to let federal officers on their properties.

Jason Schmidt owns Grazing Plains Farm in Whitewater, Kan., “an itty bitty little” farm as he refers to it, with 70 dairy cows he raises himself. Mr. Schmidt mentioned he supported the federal government’s public well being function, however wouldn’t need officers traipsing round his farm.

If he had been to see a sick cow, “I certain hope I’d report it,” he mentioned. “However there’s that little satan on my shoulder saying, ‘Simply maintain quiet and divert that milk from these sick cows and put that down the drain and don’t say something.’”

Mitch Breunig, who owns Mystic Valley Dairy in Sauk Metropolis, Wis., mentioned that if his veterinarian decided it was “prudent,” he would check a cow with fowl flu signs, however “I actually don’t need the C.D.C. coming to my farm.”

To this point, the outbreak has affected not small farms, however the large dairies that more and more dominate the trade and sometimes depend on migrant staff.

The house owners of such farms “don’t care about our well being, they only care that we do our jobs,” mentioned Luis Jimenez, who works on a dairy in upstate New York and based a bunch supporting undocumented immigrant farmworkers.

“Their cows’ well being is extra essential to them than their staff,” he added.

Farms are sometimes geographically distant, and the employees — who generally dwell on web site — could not have transportation to achieve medical care. And to many, the sorts of signs ascribed to fowl flu an infection could not appear notably pressing.

“We’re speaking about a watch an infection or a cough, and these are individuals who have again aches and arm aches and damaged this and that,” mentioned Monica Schoch-Spana, a medical anthropologist on the Johns Hopkins Middle for Well being Safety.

Even with out entry to farms, well being officers might help migrant staff in different settings, advocates famous. “They go to church, they go to shops, they go to eating places, and there are different methods to achieve them,” mentioned Amy Liebman, a program officer on the Migrant Clinicians Community.

To make testing extra enticing, group facilities might supply different well being care providers, authorized help and meals, and educate staff on methods they’ll defend themselves and their households, Ms. Liebman mentioned.

Dr. Shah mentioned the C.D.C. was working with veterinarians and organizations just like the Migrant Clinicians Community to achieve farmworkers. “We, too, want to supply testing to extra staff,” he mentioned.

On Monday, Dr. Shah requested that state well being officers present goggles, face shields and gloves to farmworkers, and collaborate with trusted group organizations to teach them on the significance of the gear in stopping an infection.

Regardless of the dangers to their well being, farmworkers will not be required to put on protecting tools. “It’s not a mandate, nobody is being pressured to do something right here,” Dr. Shah mentioned.

However the nature of farm work and the settings wherein it’s executed — milk parlors that shortly render masks moist and ineffective, for instance — could make sporting protecting tools difficult.

A number of states have taken steps to include the outbreak, with restricted success.

Texas provided to offer protecting gear to dairies, however solely 4 got here ahead, based on a spokesman for the state’s well being division. Idaho has additionally provided protecting tools for the reason that outbreak’s onset, however no farms have taken up the supply.

Idaho well being officers haven’t requested to go onto farms “for privateness and biosecurity causes,” Dr. Christine Hahn, the state epidemiologist, mentioned in an electronic mail, though they helped to check one farmworker for the an infection.

Michigan is prohibiting exhibition of dairy cows and poultry till the outbreak has subsided. The state doesn’t require testing of cows or farmworkers.

The present state of affairs has proven that dairy farms could seed new outbreaks that shortly unfold, as has lengthy been the case on poultry and pig farms, a number of specialists mentioned.

“Should you needed to conceal a novel virus emergence in the US, top-of-the-line locations to cover it might be in animal staff in rural America,” mentioned Dr. Gregory Grey, an infectious illness epidemiologist on the College of Texas Medical Department.

Surveillance of these staff is “not practically as sturdy as we’d see for different inhabitants teams,” he mentioned.

To construct surveillance networks that embrace farmworkers and their households, federal, state and native businesses must first set up belief, mentioned Dr. Andrew Bowman, a veterinary epidemiologist at Ohio State College.

“Should you have a look at the influenza surveillance we’ve executed in swine, that didn’t occur in a single day,” Dr. Bowman mentioned. “That took a decade to construct.”

Whereas surveillance is essential, some specialists cautioned in opposition to testing farmworkers with out first catering to their wants.

“If we put together to gather info that’s solely going to learn others and never essentially straight defend them, I simply assume that’s a really exhausting factor to do ethically,” Dr. Nuzzo mentioned.

Miguel Salazar contributed reporting.