Unusual avian influenza incident in Missouri shares resemblance with strain prevalent among livestock, according to the CDC.
The viral strain was uploaded to the GISAID database on a Friday, making its genetic sequence publicly accessible for research purposes. The strain is closely related to the one that has been affecting dairy cattle in 14 states this year. Despite this, the individual who tested positive in Missouri last month had no contact with wild birds, poultry, or cattle, nor did they consume raw dairy products. The origin of the infection in this case remains under investigation. Thirteen other human infections have been reported in the US this year, all in individuals who had contact with infected animals.
The potential significance of this infection is a subject of debate. On one hand, experts find it concerning that the individual was infected without apparent contact with infected animals, which seems to deviate from the usual pattern. All the other reported H5N1 infections this year have been mild and classified as dead-end infections, with no evidence of human-to-human transmission. Fortunately, contact tracing has not identified any further transmissions, suggesting that the virus lacks novel capabilities.
This observation is supported by the genetic sequence of the virus. Scientists, according to the CDC, have not identified any mutations that could indicate increased transmissibility or severity.
However, the virus did exhibit mutations that may impact the development of candidate vaccine viruses, vaccines prepared by the CDC that can be used by manufacturers in case of an outbreak.
Additional information about the Missouri case, published in the CDC's weekly FluView report, revealed that a close household contact of the infected person also fell ill on the same day, exhibited similar symptoms but was never tested. Both individuals have since recovered.
The simultaneous onset of symptoms does not suggest person-to-person transmission but rather a shared exposure, according to the CDC.
A second close contact, a healthcare worker, developed mild symptoms but tested negative for flu.
A 10-day follow-up period has passed, and no additional cases have been reported, as per the CDC.
The confirmed patient in Missouri was an adult with multiple underlying medical conditions. They fell ill during the week ending August 24, according to the FluView report.
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Dr. Nirav Shah, principal deputy director of the CDC, stated at a news briefing that the patient was admitted to the hospital due to chest pain, nausea, vomiting, diarrhea, and weakness. Shah mentioned that the patient's hospitalization was due to their underlying health conditions.
While in the hospital, the patient tested positive for an influenza A virus. The state of Missouri conducts additional testing on all specimens that test positive for influenza A, and this testing identified the patient as having an H5 virus, a rare finding. The sample was sent to the CDC for confirmation.
When asked during a briefing on Thursday whether the CDC considered the flu infection to be incidental to the patient's hospitalization, Dr. Shah responded, “no, we’re not describing it as incidental. That was a question that was on our minds, but no, it was not incidental there.”
Dr. Shah declined to provide further details, citing patient confidentiality concerns.
CDC scientists noted that the sample they received contained a low concentration of the virus, and they expressed caution about their ability to sequence all eight of the virus's segments.
Despite the ongoing investigation, the unexplained infection in Missouri has raised concerns among health experts due to the individual's lack of direct contact with infected animals. Moreover, the potential impact of the virus mutations on the development of candidate vaccine viruses is a matter of interest for public health officials.
