First person tests positive for bird flu without clear exposure to sick animals

A Missouri resident has tested positive for bird flu even though there is no evidence the person came into contact with an animal infected with the virus, the Centers for Disease Control and Prevention said in a Friday evening news release.

Acquiring the virus without animal contact raises safety concerns because it may be an indication that the potentially quite deadly virus could develop the ability to transmit from human-to-human, although the CDC still considers such a risk "low" at the moment.

The person is the 14th infected with H5N1 in the U.S. this year and the first to be hospitalized and to test positive without coming into known contact with an infected animal. The others, who were all described as having "mild" symptoms, had worked on farms known to have H5N1-infected cattle or poultry.

It's unclear how the Missouri patient was infected or how sick the virus made them. The person, who has not been identified, was hospitalized Aug. 22 and treated with an anti-viral medication after a flu test turned positive. When that test didn't match the seasonal flu, it was sent for further testing and the H5N1 result was confirmed Thursday, the CDC said. The person has since been released from the hospital and recovered.

Public health officials have been concerned about bird flu, because it has been lethal in about half of the people known to have contracted it worldwide. Other milder cases may have went undetected.

Tracing its path

The CDC will analyze the genetics of the latest patient's strain to understand if it is the same one that infected the other people and farm animals or a different one.

Understanding the origin is crucial for understanding the threat, if any, that the virus poses to the general public, said Dr. Jesse Goodman, a professor of medicine and infectious diseases at Georgetown University and a former chief scientist at the U.S. Food and Drug Administration.

If the person is infected with the same strain as the other people, there has to be a chain of transmission, either from the sick animals or from another infected person, Goodman said.

Lisa Cox, a spokesperson for the Missouri health department, said in an email that the Missouri patient's contacts remained asymptomatic throughout the observation period, so they did not pass the virus on to anyone else.

It's possible the person carries a new strain of the virus that has not been seen before. Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota, said he thinks the Missouri patient most likely caught a different strain of the virus after coming into close contact with an infected migratory bird.

Late summer is when many birds are migrating, he said, so "this is the season we're going to see that virus moving." A backyard bird feeder "is the classic example," he said. Osterholm said he doesn't know if the patient has a feeder or was exposed to one, but "that's the kind of exposure that would not be uncommon."

Controlling the risk

The current U.S. outbreak was likely sparked by a wild bird that infected cattle on a dairy farm in Texas and then spread to farms in more than a dozen other states ? but has not been previously reported in Missouri cattle. Related strains of H5N1 have been circulating in wild birds since at least 1997.

So far, humans have not shown high susceptibility to the H5N1 virus, said Dr. Paul Offit, a pediatric infectious disease expert who directs the Vaccine Education Center at Children's Hospital of Philadelphia. The only people who've fallen ill so far were those on farms exposed to very high levels of virus, which penetrated deep into their lower respiratory tract. Perhaps the person in Missouri, whom state officials described as having an "underlying medical condition," was particularly susceptible to such a lower respiratory tract infection, he said.

People, even those who have had the seasonal flu or who get annual vaccines, have no immunity to H5 flu viruses, and thus they could become quite ill if infected, Offit said.

CDC closely monitors data from influenza surveillance systems, particularly in states with known animal outbreaks. So far they've seen no sign of unusual flu activity in people, according to the release.

Goodman praised the CDC monitoring, but thinks the agency and others need to be doing more to get ahead of any potential major outbreak. "This was another warning shot," Goodman said. Just this week, Goodman, co-wrote an opinion piece in the Journal of the American Medical Association calling for more investment in public health, including in a vaccine strategy, to address H5N1 both in the U.S. and abroad.

"The time to prepare for a potential infectious outbreak is before it occurs, because when it occurs it's too late," he said. "Hopefully, it doesn't turn into a public health threat and I think that's most likely, but we need to pay attention. We can't pretend that the world will never have another pandemic."

The CDC said it continues to assess the risk to the general public from H5N1 as "low" and is not changing its recommendations related to the virus at this time.

Not enough information has been made public about the Missouri patient to understand how concerning the situation is, Offit said.

"We await critical information, as always," Offit said. "You know enough just to make you nervous but not enough to know whether you really should be nervous."

Karen Weintraub can be reached at [email protected].

This article originally appeared on USA TODAY: Missouri resident contracts bird flu with no known exposure