UPDATED November 18, 2025 // Editor’s note: This article was updated to include a newly confirmed human case of bird flu in Washington State. 

Bird flu cases are increasing, and a new review suggests the virus might spread between people without causing symptoms. But with limited surveillance and major gaps in data and reporting, the scope of the problem remains unclear.

The review, authored by CDC scientists, reported 18 asymptomatic H5N1 human cases documented (all abroad) since 2004. Two were likely due to human-to-human transmission via household contact. In their paper, the CDC authors joined calls from public health advocates and scientists for increased bird flu surveillance, which has instead been scaled back by the federal government.

“This is a call to action for public agencies to do a lot [more] surveillance,” said Diego Hijano, MD, MSc, pediatric infectious disease physician at St. Jude Children’s Research Hospital in Memphis, Tennessee. (Hijano was not involved in the review.)

What can clinicians do? Ask patients with flu-like symptoms about risk factors such as occupational exposure (poultry and dairy workers, veterinarians, or wildlife handlers), dietary exposure (unpasteurized milk or undercooked poultry), and — to a lesser degree highlighted by the new review — household exposure, infectious disease experts recommended.

“Physicians should maintain awareness but avoid alarmism,” said Rick Bright, PhD, immunologist, public health expert, and the founder of Bright Global Health.

Here’s what you need to know about bird flu right now.

Current H5N1 Situation

Fall migratory patterns are again spurring seasonal outbreaks, particularly among geese and swans at public parks. Since September, 42 US states have confirmed wild bird cases. Nearly 4 million commercial poultry were culled in September, plus another 4 million in October due to flock outbreaks — a sharp increase from just 60,000 birds culled in August. Since 2024, 18 US states have had confirmed dairy cattle infections, including Nebraska’s first documentation in September.

Since 2022, the CDC has confirmed 71 human cases of bird flu, including two nonfatal cases in California with unknown exposure sources and one death in January of a person in Louisiana exposed to backyard and wild birds.

In early November, an older adult with underlying conditions in Washington State tested positive for a rare bird flu strain called H5N5, according to the Washington State Department of Health. The person, who was hospitalized and is the first human case with the strain, kept backyard poultry that were exposed to wild birds.

The current practice in the US — and globally — is to initiate human testing when a person has been exposed to sick animals and is symptomatic. 

Many US scientists and public health experts are calling for expanded human testing. CDC data show that since 2022, 18,700 people have been monitored after exposure, with approximately 880 people tested.

“If you’re only testing 5% of exposed individuals…you’re going to miss some human cases,” said Leonard Mermel, DO, professor and a respiratory pathogen expert at Brown University, Providence, Rhode Island. Brown’s hospital system and emergency department include screening questions because they “don’t want to miss the case that could lead to an outbreak.”

Of the 70 human cases, six were detected through the national flu surveillance program, which screens for A(H5) and other novel flu viruses. This shows how important broad surveillance is for early detection: Without it, those six cases likely would have gone unnoticed. Experts say more robust surveillance, particularly among farm workers who may be asymptomatic, would likely uncover additional mild or asymptomatic cases. 

“Limited surveillance and delayed data sharing are leaving blind spots,” said Bright, who coauthored a commentary that was published alongside the scoping review. “Because current US surveillance focuses primarily on symptomatic individuals, the true number of human infections may be underestimated.”

In dairy cattle studies, 60% of cows exposed to H5N1 were infected but didn’t show any symptoms, said Diego Diel, DVM, MS, PhD, professor at Cornell University College of Veterinary Medicine, Ithaca, New York.

Despite these concerns, there’s no evidence so far to suggest that the virus can spread efficiently among humans, and the threat to public health remains low, according to the World Health Organization.

Tips for Clinical Practice

“Clinicians on the front line are at greater risk of unknowingly seeing [bird flu],” said Mermel. They “therefore should be more vigilant and open-minded to potential exposure.”

Be aware of what public health officials are doing in your area to monitor for bird flu, said Dean Blumberg, MD, chief of the division of pediatric infectious diseases at UC Davis Health in Sacramento, California.

“In my area, when we have patients who test positive for influenza — specifically for influenza A — if it’s not able to be typed, then it does undergo further testing,” Blumberg said. “I don’t have to order that…it’s what the lab is going to do. And they’re going to work with the county and state public health so that if it is avian influenza, they’re going to detect that. Clinicians need to be aware of [whether] those protocols are in place in their area.”

Experts offered these tips:

• Incorporate risk assessment for bird flu into your influenza-like illness triage questions, said Bright. Ask patients about animal and dietary exposures.
• For those at risk for animal exposure, remind them to wear protective gear and practice good hygiene.
• Discourage consumption of unpasteurized milk or cheese and undercooked eggs and poultry. A recent study in ferrets — a “highly relevant model for influenza,” said Diel, senior author of the study — revealed that liquid matrices, such as raw milk, may be especially infectious.
• Ask about cats and bird feeders. Domestic cats “are highly susceptible,” either from eating an infected bird or from exposure to raw dairy, Diel said. Another potential exposure is handling bird feeders because wild birds shed the virus in their feces.
• Encourage seasonal flu vaccination to reduce the risk for viral reassortment.