Be Alert for Conjunctivitis: New Human Cases of H5N1 Bird Flu

This transcript has been edited for clarity. 

We're now in the midst of a multistate outbreak of influenza A H5N1 bird flu in dairy cows and other animals. USDA has confirmed outbreaks in more than 130 dairy herds across 12 states, and also in a herd of alpacas. CDC has confirmed three human cases of bird flu in dairy farm workers. 

The first case, on April 1, 2024, was the first-ever known case of cow-to-human transmission of bird flu viruses in the United States and globally, and it was the second-ever documented human case of bird flu in the United States. The first US case was in a poultry worker in Colorado in 2022. The chief complaint for the first two patients in that outbreak was conjunctivitis. The third patient had more typical flu symptoms, including a cough. All three of these patients had direct contact with infected cows. On July 3, 2024, a fourth human case of H5N1 bird flu, tied to the dairy cow outbreak, was identified in Colorado. This patient only reported eye symptoms. 

Over the past 27 years, more than 900 sporadic bird flu cases in humans have been reported worldwide. Overall, 52% of them have been fatal. CDC says to avoid exposure to sick or dead animals. They also recommend wearing appropriate personal protective equipment for job-related exposure to infected or potentially infected animals. 

Several questions come to mind. Is our milk supply safe? FDA says yes. PCR testing of milk samples did find genetic pieces of the virus, but they're not infectious. Pasteurization seems effective at killing this virus. This supports the safety of our commercial pasteurized milk supply, but not so for raw milk. So, people should avoid raw milk and any products made from it. 

What about beef? USDA says our meat supply is safe. Even so, they've continued testing, and on Friday, May 24, bird flu was detected via PCR in beef muscle from a second condemned cow. However, results of a USDA ground beef cooking study are reassuring. In this study, high levels of virus were injected into large ground beef patties. The patties were then cooked to different temperatures — 145° F (medium) and 160° F (well done). No virus was present in the burgers cooked to either temperature. The bottom line is that people should be careful handling raw meat and cook their meat to a safe internal temperature. No steak tartare. 

Here's the good news. Currently available flu test kits can detect H5, but they can't distinguish bird flu from seasonal flu. Current flu antivirals seem to be effective against it, and if we do end up needing a new dedicated vaccine, we already have two candidate vaccine viruses that should provide good cross-reactivity.

CDC says that the risk to the general public, at least for now, is low. But CDC remains on high alert and is asking health partners to help raise awareness to physicians. Consider bird flu in patients with conjunctivitis and or other respiratory illness after relevant exposures. If this H5N1 virus starts to mix and mingle with the seasonal flu virus, we could really get into a mess. So please get your seasonal flu vaccine in the fall.