Federal officials have maintained that the nation's bird flu outbreak does not pose an immediate threat to public health, but infectious disease experts say recent developments indicate the H5N1 virus' spread is widening — and with it, the risks it poses to humans.
"The traffic light is changing from green to amber," Peter Chin-Hong, MD, an infectious disease expert at University of California at San Francisco, told NBC News. "So many signs are going in the wrong direction."
Here’s a recap of the scope of the outbreak and recent developments that have heightened concerns among experts:
- Since late March, the H5N1 outbreak has affected at least 875 herds of dairy cows in 16 states, according to the CDC. This year marked the first time bird flu viruses have been found in cows. As for human infections, 64 have been confirmed in the U.S. since April, mostly among individuals who work with dairy cattle and poultry. Most patients with a confirmed case have reported mild symptoms.
- In recent months, fragments of the virus have been detected in wastewater, indicating the virus' spread is much wider than what official numbers suggest. About 19% of sites tested as part of the CDC's National Wastewater Surveillance System in 10 states have returned positive detections in early December. Most detections have been in areas where there are dairy and poultry farms, but there have been cases where positive detections surface in areas with no agricultural facilities.
"We've seen detections in a lot more places, and we've seen a lot more frequent detections," in recent months, Amy Lockwood, PhD, told NBC. She leads detection efforts at Verily, the company providing wastewater testing services to the CDC. "We are starting to see it in more and more places where we don't know what the source might be automatically," Ms. Lockwood said. "We are in the throes of a very big numbers game."
- Another factor sounding alarm bells among experts: Several human cases with no confirmed source of infection. In September, the CDC confirmed a case in a Missouri resident who did not have any known occupational exposure to infected animals. Two months later, a child in California became ill with H5N1 with no initial confirmed infection source.
- On Dec. 18, the CDC confirmed a patient in Louisiana has been hospitalized with a severe bird flu infection, marking the nation's first human case of severe illness tied to H5N1. The individual, who is older than 65 and has underlying medical conditions, was exposed to sick and dead birds in backyard flocks.
- The more the virus spreads, particularly among mammals, the more opportunities it has to evolve in ways that make it more adept at spreading to and among humans. A study published Dec. 5 in Science gave weight to that concern, suggesting that the version of the virus circulating in dairy cows is a single mutation away from being able to more easily bind to human receptors.
- Taken together, these developments have put H5N1 on the path to becoming the next potential pandemic, according to public health experts, who are urging federal agencies to bolster testing and surveillance efforts to better prepare and respond to the possibility that the virus gains the ability to spread from person to person.