Testing of samples taken from a child in California thought to have contracted H5N1 bird flu after drinking raw milk turned up no evidence of influenza viruses, the Centers for Disease Control and Prevention said Thursday.
A test run on a sample from the child — who went to a Marin County emergency department last week with a fever and vomiting — had been positive there for flu A. The sample was sent to a local laboratory as well as the California Department of Public Health’s lab to see if the virus was one of the seasonal flu viruses, H1N1 and H3N2, or H5N1, which have infected hundreds of dairy herds in the state.
When neither lab could confirm the positive result, a sample was sent to the CDC to see if its technicians could identify the virus. They could not.
“The sample was negative for all flu targets,” Kevin Griffis, director of the CDC’s office of communications, told STAT on Thursday.
That outcome does not definitively rule out the possibility that the child had an H5N1 infection, but it does mean he or she will not be added to the list of confirmed human cases in the U.S.
Lisa Santora, public health officer for Marin County, said she wasn’t surprised by the outcome, because the amount of virus in the original test sample was low. Samples degrade over time, so sometimes tests that are positive in a state or local lab cannot be confirmed by the time they reach the CDC. Santora said locally the child will be classified as a suspected case.
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This incident is likely not the last time a situation like this will arise, warned Michael Osterholm, director of the University of Minnesota’s Center for Infectious Disease Research and Policy.
Osterholm said with flu season beginning, and with the popularity of raw milk in some segments of the California population, it’s likely doctors and emergency departments will see other people with influenza-like illness who have consumed raw milk. “I think we have to be careful about interpreting these as we go forward,” he said.
Santora said as flu activity starts to pick up it will be important for health professionals to get clear exposure histories for patients with influenza-like illnesses, to determine if they had exposures to potentially infected animals or have consumed raw milk.
“This is the time for us, based on lessons learned in the past, to up our surveillance systems that we know have capabilities to engage in early detection,” she said.
To date this year the CDC has confirmed 58 human cases in seven states. Most were workers on infected dairy farms or people involved in culling infected poultry. In addition, there were six people who tested positive for H5 in the state laboratories of California, Washington, and Arizona. But the quality of the samples for those six people were such that CDC’s laboratories were unable to confirm the infections.
Had the CDC confirmed the child’s infection, it would have been the first H5N1 case linked to raw milk consumption in the United States.
The toddler had drunk raw milk produced by a company called Raw Milk LLC. The company’s products have recently been quarantined because some of its products on store shelves as well as milk at its farm had tested positive for H5N1.
Lisa Santora, public health officer for Marin County, said Wednesday that it appears that the family had been unaware when they purchased the milk and gave it to the child that it was unpasteurized. The milk of cows infected with H5N1 contains high levels of the virus, but studies have shown that commercial pasteurization kills the virus.
When a family member told the doctor tending to the child about the raw milk consumption, a flu test was ordered. An initial test, using a swab swirled around the child’s nostrils, was negative, but a second was ordered a day later. That test, using a swab rubbed around the child’s mouth and throat, tested positive for flu A. That was the only test in this investigation that was positive for influenza.
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Santora said family members of the child were also tested for flu, but all were negative. The child, who did not have classic flu symptoms, has since recovered.
Scientists who study H5N1 have been worried about what might happen to people who drink unpasteurized milk laced with the virus, based on evidence from some animals. Cats on farms with infected cows have died from drinking raw milk; a study earlier this year showed that mice fed infected raw milk became so ill they had to be euthanized.
Last month a child in Alameda County, Calif., tested positive for H5N1. It has not been determined how the child, who had only mild symptoms, became infected with the virus.
California is currently the epicenter of the outbreak of H5N1 in dairy cows, with over 600 herds having tested positive for the virus since spread there was first detected in late August. Nationally, 832 herds in 16 states have tested positive for the virus since the outbreak in cows was first confirmed in late March.
