A second health care worker who cared for a person hospitalized in Missouri with H5N1 bird flu developed mild respiratory symptoms but was not tested for the flu, the Centers for Disease Control and Prevention reported. on Friday.
The CDC said Missouri health officials only learned the health care worker had symptoms after the individual had recovered, too late to perform a diagnostic test.
“CDC is maintaining close communication with the State of Missouri in its ongoing investigation of the positive H5N1 case there, including regarding the identification of an additional symptomatic close contact,” an agency spokesperson told STAT via email. “The finding does not change the CDC’s assessment that the risk to the public remains low.”
This is the second time that possible cases linked to the confirmed case have come to light long after the fact. Last week it was announced that a household contact of the confirmed case and a healthcare worker who had cared for the individual while he or she was in hospital had also been ill. That first healthcare worker tested negative for influenza.
In the case of the household contact, the person became ill the same day as the confirmed case, virtually eliminating the possibility of the virus spreading between these two people. Instead, it suggests that if the second person was indeed also infected with H5N1, he or she had the same exposure to the virus as the confirmed case.
It is still not known how this person contracted H5N1. While a number of US states have seen the virus spread among cows, Missouri has not reported any infected dairy cattle or any recent poultry outbreak involving the virus.
The Missouri individual was hospitalized on August 22, although the case was not publicly reported until September 6, after the individual had been released from the hospital and recovered.
STAT has attempted to contact the Missouri Department of Health and Senior Services several times over the past week to inquire about the status of the investigation into this case. Late Friday, after the first version of this article appeared, the agency responded.
“The investigation is ongoing and health care providers who may have had contact with the case have been identified and are being followed up,” department spokesperson Lisa Cox said in an email.
Missouri is conducting the investigation. The CDC can only send its disease investigators if invited by a state, and Missouri has not issued an invitation.
The CDC reported on the new health care worker in an influenza “spotlight” posted on its website Friday.
The update revealed that Missouri has collected blood samples from both the confirmed case and the household contact. Those samples will be used for what is known as serological testing – looking for antibodies that can confirm previous infection with the H5N1 bird flu. The samples are sent to the CDC for analysis.
The CDC said the newly identified healthcare worker will also be asked to submit a blood sample for testing. Asked whether health care workers have agreed to provide blood samples for antibody testing, Cox said: “We should know more next week.”
Michael Osterholm, director of the University of Minnesota’s Center for Infectious Diseases Research and Policy, said there could be another explanation for this health care worker’s illness. At the time the confirmed case was in hospital, there was a high level of respiratory illness, including high levels of Covid-19 activity.
“We’ll have to see what the serology shows,” Osterholm said.
This news emerged as California announced it had found it seven more infected dairy herds, bringing the number of affected farms in the state to 17, and the cumulative number of infected herds in the country to 215 across 14 states. The outbreak in cattle was first confirmed in late March.
Determining how widespread the virus is in dairy herds is a challenge because many farmers have resisted testing their animals and see no benefit in linking their operations to the outbreak. However, some took and stored samples from sick cows earlier in the outbreak and only recently submitted them for testing, after a federal program that compensates farmers for losses in milk production took effect. At least seven herds have been retroactively confirmed in this way.
Fourteen human cases have been discovered so far this year, including four in farm workers who handled livestock, nine in people who worked culling infected poultry, and the Missouri case. There have been multiple reports of symptomatic workers not being tested, and there is widespread belief that the 14 confirmed cases represent only part of the human infection picture.
In an effort to further explore this issue, the CDC and the Ohio Department of Health are working a serological study of veterinarians and other veterinary professions, taking advantage of a meeting of these professions at the recent annual conference of the American Association of Bovine Practitioners in Columbus, Ohio.
Blood samples and questionnaires were collected from approximately 150 veterinarians and others from 45 states who work with cows. The goal is to see if there have been undetected infections among these individuals.
This article has been updated with comments from the CDC and the Missouri Department of Health and Senior Services