From the earliest days of the H5N1 bird flu outbreak in dairy cattle, experts watching the evolving situation have worried about California. 

The Golden State has the country’s largest concentration of dairy farms, roughly 1,100 herds. The concern has been if the virus got into California, the prospects for spread would be huge and containment a challenge.

And, indeed, in the roughly five weeks since California’s first infected farms were confirmed, those fears have proved to have been well-founded. As of Monday, 82 farms have tested positive for H5N1, vaulting California over Colorado as the state with the most infected herds. By comparison, Colorado has counted 64 infected herds over the course of six months. (It should also be noted that California’s Department of Food and Agriculture is actively looking for affected herds; many other states are not.)

Infected cows could in turn infect people. California has already detected three human infections in workers who had exposure to infected cows. (The Centers for Disease Control and Prevention has yet to confirm the third case.)

STAT recently spoke to Erica Pan, California’s state epidemiologist, about what public health officials are doing to monitor for human H5N1 infections. The conversation, which took place before California announced its human cases, has been lightly edited for clarity and length.

Has California been proactively looking for H5N1 infections among farmworkers and others, given the rapid rise in infected farms in the state?

Ever since March or April [when H5N1 in cows was first confirmed in the U.S.] we have been very actively watching and preparing and working with our California Department of Food and Ag. Typically, seasonal flu surveillance really decreases over the summer but we —like many other states — kept up our flu surveillance and sent out a health advisory to clinicians in California, saying: Please still test for flu, even though it’s summer. Please be asking these questions about animal exposures.

And then we were trying to reach goals of the numbers of flu specimens we would be subtyping of flu A, to confirm that the flu that is still circulating is seasonal flu and not H5N1. So we’ve been meeting our goals over the summer on that. 

In addition, once we’ve had these positive herds in California, we’ve worked closely with our local health departments on the ground where these actual farms and premises are, who are then working with the farms and the farmworkers to monitor individuals who might be exposed and monitoring for symptoms. Really working to talk to the employees and the farmers about “This is a health check. The goal is not government monitoring. It is really to do a health check to make sure you are feeling well. And if you’re not, we can help get testing and treatment if needed.” 

We, of course, had a lot of experience since 2022, when we had huge [H5N1] poultry outbreaks, so thankfully a lot of the local health departments at least had experience with that as well — acknowledging that dairy farmers are often different, though.

One of the things a lot of affected jurisdictions have had to grapple with is the fact that there’s been a fair amount of reluctance on the part of the farmers and farmworkers to interact with the public health side. Are you getting cooperation or are you facing suspicion and unwillingness to interact?

A lot of this work happens on the ground with our local health departments. And what we’re hearing from them is that it’s a big spectrum. There are definitely some farms that are the most collaborative and open and welcoming. And I think there are some that are challenging.

We’re working with some of the farmworker organizations, and I think we’re improving. I think local health departments are working more closely with their agricultural commissioners and some of these other worker organizations to really get more of their input and support — especially in areas where there may be more concern about what the role of public health is.

We are not only working on outreach and education around personal protective equipment but have distributed a lot. We’ve distributed over 300,000 respirator masks, gloves, goggles, and face shields to protect farmworkers from bird flu and have tried to offer that as well as a way to engage the workers and the worker organizations.

One of the things the CDC is also trying to do is get seasonal flu shots into farmworkers in states where it’s known that there have been outbreaks in cows. Is that happening at your level? Or is it happening at the local health department level?

Both. CDC did give us an additional allocation of CDC-funded seasonal flu vaccine for farmworkers. For our entire state, we’ve only gotten about 5,000 more doses. It’s not a huge amount. But it’s certainly helpful. So we are definitely working with the farms in the Central Valley where we have both the highest intensity of dairy farms and where our positives [herds] have been detected. And in general our local health departments are trying to figure out how to provide more influenza vaccinations in that community as well.

Five thousand doses? There are more than 1,000 dairies in California. Is that the only allocation you’re getting?

That’s the allocation that’s been associated with this bird flu H5N1 effort.

We have some state-funded vaccine that is for high-risk uninsured and underinsured people, which historically is distributed to the underinsured elderly living in congregate settings and other places. We typically do use all that vaccine in that high-risk population. So, yeah, I think we’re working on and thinking about other creative solutions, especially if there are workers in smaller farms, etc., that don’t have other health care access.

And it will be interesting to see what the uptake is [among farmworkers offered flu shots].

Do you have a sense of whether this is a population that takes flu shots normally?

I don’t offhand. I do know that in general only about half of people get a flu vaccination. So we have concerns that it may not be a population that typically has high uptake.

What about studies? There’s been a lot of interest in trying to test blood samples from farmworkers looking for antibodies to see if there have been more infections than have been detected. Is California trying to do that?

I think we’re learning from other states that have gone before us. And our understanding from Michigan, for example, is that it took them a little bit to develop these relationships, work with individuals to then get the engagement to do that. It’s still relatively early for us. It’s been about a month.

But we’re certainly interested and open to that and the CDC has indicated that they would absolutely support [that kind of work].

It is my understanding that some of the USDA resources that farms can apply for if they have been impacted also have inclusive language about collaborating with local public health and participating in CDC studies. So I think we do want to start to work on that soon. But I think right now, we’re really kind of working on just solidifying some of those relationships and working on encouraging overall health monitoring, health checks, etc.

How big an issue is raw milk in California and how worried are you about it in terms of people’s exposure to H5N1?

It definitely has been top of mind. 

For a lot of the details you’ll have to refer to the California Department of Food and Ag. But they do regulate. There are a few raw dairy farms in California and they do regulate them at the state level. And they’ve been requiring testing — for several months at this point. Definitely before we had these other commercial detections.