The CDC has confirmed the nation's first case of bird flu in a person who had no known occupational exposure to infected animals, the agency said Sept. 6.
The adult patient, a Missouri resident, was hospitalized Aug. 22 and has since recovered, according to federal and state health authorities. The individual had underlying medical conditions and was treated with an influenza antiviral. State officials have said no transmission among close contacts or others has been identified, though an investigation is ongoing.
This marks the 14th human case of H5N1 avian influenza reported in the U.S. this year. The other 13 patients were all exposed to infected dairy cows or poultry. The CDC said its current assessment is that the risk bird flu poses to public health remains low, but it noted that results from an investigation on the Missouri case will inform whether guidance changes are needed.
"The question now is: How did this patient acquire the infection?" William Schaffner, MD, an infectious diseases expert at Nashville, Tenn.-based Vanderbilt University Medical Center, told NBC News. "We need a very, very thorough investigation" to ensure the virus has not acquired mutations that make it more transmissible among humans.
"This will be of enormous interest," Dr. Schaffner said.
The H5N1 outbreak has affected nearly 200 dairy herds in 14 states since late March, according to the CDC. Health officials have been following the outbreak and have reiterated there is no evidence human-to-human transmission is occurring, though infectious disease experts have raised concern that the nation is not conducting enough testing to quickly identify and respond if and when that does occur.
"I'm really glad we have a robust flu system that picked this up, but [it] just begs the question: How many cases have we missed?" Katelyn Jetelina, PhD, a California-based epidemiologist who has been closely following the avian flu outbreak in dairy cattle and poultry, told The Washington Post. "In these situations, we can't fly blind. If we have a full picture, we can better act, communicate and prevent."
A preliminary genetic analysis of the virus sample in the Missouri case did not show evidence of changes that would make the virus more transmissible to humans, a federal health official who spoke on the condition of anonymity since the investigation is ongoing, told The Washington Post.
The Missouri case is also the first time the country's flu surveillance system has detected a case of H5 bird flu, the CDC said. A specimen from the patient first tested positive for influenza A but tested negative for seasonal subtypes, which triggered further testing.
"CDC continues to closely monitor available data from influenza surveillance systems, particularly in affected states, and there has been no sign of unusual influenza activity in people, including in Missouri," the agency said.