The latest on bird flu: What to know about human cases, vaccines and more

The latest updates on bird flu. (Getty Images)
The latest updates on bird flu. (Getty Images)

A second Michigan dairy farm worker has contracted bird flu, bringing the number of cases in the United States this year to three, and the total ever detected in the U.S. to four. The latest case stands out because the worker developed a cough, marking the first time this year bird flu has led to flu-like symptoms in a human, the Centers for Disease Control and Prevention said in a May 30 statement. Pink eye and fatigue were the only symptoms in this year's previous infections.

U.S. health officials are "preparing for the possibility of increased risk to human health" due to bird flu, the Centers for Disease Control and Prevention said in a May 24 statement. In April, the CDC confirmed the first human case of the year, a dairy farm worker infected in Texas. All infected individuals had prolonged close contact with infected cattle. The CDC maintains that the risk to the general public is still "low," but the CDC has also warned that, if it isn't contained, the bird flu virus could mutate, "potentially causing a pandemic." Already, the Department of Health and Human Services has set plans in motion to make 4.8 million doses of bird flu vaccine, CIDRAP reports.

Dairy cattle herds have been infected in Texas, Colorado, Idaho, Kansas, Michigan, New Mexico, North Carolina, Ohio and South Dakota. Cases in birds in New York City parks and green spaces have also been confirmed by Icahn School of Medicine at Mount Sinai researchers.

How concerned should you be about bird flu, and what might this mean for the food supply? Here’s what you need to know.

Bird flu — clinically known as influenza A (H5N1) — is a variation of flu virus that spreads primarily among birds and poultry and can be highly contagious and even fatal among birds, according to the CDC. Occasionally, the virus will jump to other animals if they eat infected birds or drink water contaminated by the feces of infected birds, the CDC says. That has become more common in recent years. Viruses are constantly mutating, and the more they spread, the more they mutate. A recent family of variants may be particularly adept at infecting other animals, including cattle, according to the World Health Organization.

It’s rare for the virus to infect humans, and when it does happen, it’s usually confined to one person who was in close contact with an infected animal and doesn’t spread to others. Bird flu may cause mild to severe sickness in humans, and it has the potential to cause pneumonia and severe, sometimes fatal lung inflammation. Since 2020, there have been 26 cases in humans confirmed by the WHO, seven of which have been fatal.

Three people have been infected in this year's outbreak among dairy cattle, making a total of four people in the U.S. who have had the virus ever. (The first-ever U.S. case was in a poultry worker who contracted the virus in 2022 while culling infected birds and recovered after experiencing only mild fatigue.)

The third and latest person infected this year is the second case in Michigan. The latest person is also a dairy farm worker who is thought to have contracted bird flu from a dairy cow. But, unlike in this year's other two cases, the worker had a cough, the first time officials have seen respiratory symptoms in the latest outbreak. The first infected Michigan dairy farm worker was being closely monitored after coming in contact with infected dairy cattle when they tested positive. Their only symptom was pink eye, and they initially tested negative for H5N1 when their nose was swabbed. However, an eye swab confirmed that they had bird flu. They have since made a full recovery.

The first human case of 2024 (and second case ever) detected in the U.S. was a dairy farm worker in Texas, who was diagnosed in late March after developing pink eye. Eye inflammation was the only symptom the Texas dairy worker experienced; they never developed any respiratory symptoms that health officials might have expected with bird flu.

No other human cases have been confirmed in the U.S., but wastewater testing revealed bird flu had found its way into Texas’s sewage system beginning as early as March — nearly a month before the first human case was uncovered. The testing has found bird flu in 19 of the 23 places that have been monitored, CNN reported. But it’s unclear if the virus found in sewage came from cattle, birds or humans. Experts told The Atlantic that they suspect that there have likely been more undiagnosed cases in dairy farm workers. The CDC on May 24 urged stepped-up global surveillance to detect such cases, and told doctors to consider bird flu as a potential cause when patients who have had possible contact with animals — such as at an "agricultural fair" — present with pink eye or respiratory symptoms.

Meanwhile, Australia has reported its first ever human case of bird flu. A child who had traveled to India tested positive in March and had a “severe infection,” officials said, but has since recovered.

The federal government is providing $200 million to help stem transmission, Reuters reported on May 10. The CDC has also requested that states provide personal protective equipment (PPE) to dairy farm workers who might be at risk, according to an emailed statement. Federal funding will provide each affected farm with up to $28,000 a day toward measures to slow the spread among animals and prevent transmission to humans, CNN reported. Health agencies will also get $101 million for continued food safety monitoring.

Dairy and poultry farm workers remain the CDC's main concern. On May 6, the agency asked state health and agriculture departments to provide PPE to dairy farm workers at risk of contracting bird flu in an effort to prevent any additional cases, the agency said in an emailed statement. But many at-risk farmworkers have yet to receive their protective gear, Reuters reported on May 23. The CDC has also asked state health officials to take other steps like making sure they have bird flu tests available to confirm possible infections. It also said health officials should stay in close contact with veterinarians and agriculture department officials and asked to be notified of any "challenges" states encounter.

For the general public, the risk remains low, the CDC says. Although human bird flu cases are extremely rare in the U.S., the CDC has asked states to step up their monitoring for the virus. Summer brings a lull in cases of common human flu, so testing often falls off. But, on May 21, the CDC said states should keep their monitoring at peak levels, testing positive flu samples to see if the illness was caused by H5N1.

After particles of the bird flu virus were discovered in about 1 in 5 samples of grocery store milk, further Food and Drug Administration testing has confirmed that the virus was inactivated by pasteurization, a sterilizing process used on more than 99% of the commercial milk supply. The U.S. Department of Agriculture also tested ground beef for bird flu, and all the samples came back negative.

Bird flu has also been found in unpasteurized milk, but you shouldn’t consume unpasteurized milk or cheese regardless, the CDC warns, because they carry risk of infections like listeria. The CDC also says that the risk of being infected from eating eggs is low, and properly cooking them would kill any virus anyway.

Farms are prohibited from selling products — including milk and eggs — from sick animals, so it’s unlikely that contaminated food would wind up on grocery store shelves. The most likely impact of the bird flu outbreak in animals on the food supply is rising prices. Egg prices have shot up as chickens have been culled or died, limiting the supply of eggs. Milk prices could see increases but are stable so far.

On April 15, Colombia became the first country to restrict the importation of beef and beef products from U.S. states with infected herds, Reuters reported. CDC tests have shown that properly cooking beef kills the bird flu virus and the agency says that the food supply is safe. However, on May 24, the USDA announced in a press statement that bird flu virus was detected in meat from one sick dairy cow that had been culled (meaning the meat never would have been sold). All other 95 samples tested by the agency were negative.

Yes. According to a CIDRAP report on May 22, the U.S. government could have the 4.8 million doses of bird flu vaccine ready in a month or two. One of the two candidate vaccines the U.S. government stockpiles appears to be a good match against the currently circulating virus, officials say. The shot will only be distributed if the current outbreak takes a turn for the worse by, for example, spreading from person to person, spreading more easily and often from animals to humans, if cases are confirmed in people with no contact with dairy cattle, or if human illnesses from bird flu become more severe, officials said.

Avoid close or prolonged contact with wild birds, cattle or any other animal suspected of being infected. The CDC also recommends steering clear of surfaces that may be contaminated with raw milk, animal feces, litter or anything else that might have crossed paths with an infected animal.

Cooking poultry and eggs to an internal temperature of 165˚F will kill off any virus. It's also recommended for milk drinkers to consume only pasteurized milk to prevent contracting bird flu or other viruses or bacteria from raw foods, and to avoid raw or undercooked foods sourced from animals that may be infected with bird flu.

This article was originally published on April 4, 2024. It has since been updated.