Update: Human Infection with Highly Pathogenic Avian Influenza A(H5N1) Virus in Texas

Summary

What CDC knows

H5N1 bird flu has been spreading in wild birds and causing outbreaks in poultry with infections in a growing number of other animals worldwide. It is now causing a multi-state veterinary outbreak in the U.S. in a new animal: dairy cows. In addition, there has been one confirmed human infection in a person who works with cows. CDC has been tracking and evaluating H5N1 bird flu for decades and is actively engaged with these recent developments because H5N1 bird flu has the potential to infect more humans and become a more widespread problem. Preliminary epidemiologic and laboratory data are reassuring, leading CDC to conclude that the current H5N1 risk to the general public remains low.

What CDC is doing

CDC is working with USDA, FDA, and state health departments to monitor people who may have been exposed to H5N1 bird flu infected animals and test people who develop symptoms. CDC has updated and expanded its recommendations for the prevention and control of H5N1 to include measures for people that are exposed to other animals, including cows, that may be infected with this virus. The CDC lab has sequenced and analyzed the virus from the person who tested positive for H5N1, published a summary of their findings, and provided the full sequence of this virus to public databases. The virus from the Texas human case is very similar compared to those from poultry and impacted cattle, with only a few minor changes. There is no evidence of genetic adaptation that would make the virus more likely to spread from person-to-person. Additionally, the virus is picked up by CDC tests, susceptible to currently available flu antiviral medications, and at this time, there is no sign of person-to-person spread of this virus. CDC will continue to remain engaged with this situation.

Current Situation

On April 1, 2024, Texas reported a human infection with highly pathogenic avian influenza (HPAI) A(H5N1) virus (H5N1 bird flu) after confirmation by CDC. This is the first time this virus has been found in a cow and the second human case of H5N1 bird flu reported in the United States. There was a previous case in 2022 in Colorado in a poultry worker. This new case is associated with a multi-state veterinary outbreak of H5N1 bird flu in U.S. dairy cows. This case occurs amid ongoing outbreaks of H5N1 bird flu in U.S. poultry, sporadic infections in a growing number of animal species, and widespread circulation of this virus in wild birds globally.

The person in Texas with H5N1 bird flu who had exposure to presumably infected cows reported eye redness, or conjunctivitis, as their only symptom and is recovering. The patient was told to stay at home away from others and was treated with a flu antiviral drug. Human infections with H5N1 bird flu are rare, but they do happen, most often after unprotected exposure to infected birds when enough virus gets into a person's eyes, nose, or mouth, or is inhaled, or when a person touches something that has virus on it and then touches their mouth, eyes, or nose. The case in Texas would be the first known instance of a person getting bird flu from a cow. It's not clear at this time exactly how the person in Texas became infected. Bird flu illnesses in people have ranged from mild (e.g., eye infection, upper respiratory symptoms) to severe (e.g., pneumonia, multi-organ failure, death).

CDC does not believe these developments change the overall H5N1 bird flu human health risk for the U.S. general public, which CDC continues to believe is low. CDC has preliminary analysis of genetic sequences showing that these viruses remain primarily avian and are not well adapted to people. There were no changes that would make these viruses resistant to current FDA-approved and recommended flu antiviral medications. These viruses also are very closely related to two existing HPAI A(H5N1) candidate vaccine viruses that are already available to manufacturers, and which could be used to make vaccine if needed.

Viruses can undergo changes when they replicate after infection, and CDC scientists look for changes any time they study a virus. In this case, CDC scientists did identify a previously characterized change in one amino acid associated with human and other mammal infections. This finding is not uncommon or surprising and, importantly, is not associated with an increased ability of this virus to spread between people.

In addition to studying the virus, CDC analyzes whether people may be seeking more health care in areas where the virus might be spread. Although increases in health care use are unlikely in this situation, in an abundance of caution, CDC reviewed available public health surveillance data sources in the states with affected dairy farms and did not detect any evidence of increases in influenza A positive tests or influenza-related medical visits.

Recommendations

While CDC believes the current risk to the general public remains low, people with close or long unprotected exposures (not wearing respiratory or eye protection) to infected birds or other animals (including livestock), or to environments contaminated by infected birds or other animals, are at greater risk of infection.

To reduce the risk of infection:

• People should avoid unprotected exposures to sick or dead animals, including wild birds, poultry, other domesticated birds, and other wild or domesticated animals (including cows).
• People should avoid unprotected exposures to animal poop, bedding (litter), raw milk, or materials that have been touched by, or close to, birds or other animals with suspected or confirmed H5N1 bird flu.
• People should not prepare or consume uncooked or undercooked food or related uncooked food products, such as unpasteurized (raw) milk, or raw cheeses, from animals with suspected or confirmed H5N1 bird flu virus infection.
• It is safe to drink commercial milk because products are pasteurized before entering the market. Pasteurization kills bacteria and viruses, like influenza viruses, in milk.
• It is safe to eat properly handled and cooked poultry in the United States. Properly handling and cooking poultry and eggs to an internal temperature of 165˚F kills bacteria and viruses, including bird flu viruses.
• Specific recommendations for farmers; poultry, backyard flock, and livestock owners; and worker protection are also available.