Testing of samples taken from a child in California suspected of contracting H5N1 bird flu after drinking raw milk found no evidence of influenza viruses, the Centers for Disease Control and Prevention said Thursday.
A test on a sample from the child — who went to the Marin County emergency department last week with fever and vomiting — came back positive for influenza A. The sample was sent to a local lab, as well as to the California Department of Public Health Health’s lab to see if the virus was one of the seasonal flu viruses, H1N1 and H3N2, or H5N1, that 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 technicians could identify the virus. They couldn’t.
“The sample was negative for all flu targets,” Kevin Griffis, director of the CDC’s communications office, told STAT on Thursday.
This outcome does not definitively rule out the possibility that the child had an H5N1 infection, but it does mean that he or she will not be added to the list of confirmed human cases in the US.
Lisa Santora, public health officer for Marin County, said she was not 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 that the child will be classified as a suspected case.
This incident is unlikely to be 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 that as flu season begins and with the popularity of raw milk in some parts of the California population, it is likely that doctors and emergency rooms will see other people with flu-like illness who have consumed raw milk. “I think we have to be careful about interpreting this as we move forward,” he said.
Santora said that as flu activity begins to increase, it will be important for health care workers to obtain clear exposure histories from patients with flu-like illnesses to determine whether they have been exposed to potentially infected animals or consumed raw milk.
“Now is the time for us, based on the lessons learned from the past, to improve our surveillance systems that we know have the ability to detect early,” she said.
So far 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 labs of California, Washington and Arizona. But the quality of the samples for those six people was such that CDC labs could not confirm the infections.
If the CDC had 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 been drinking raw milk produced by a company called Raw Milk LLC. The company’s products were recently quarantined because some products on store shelves and milk on the farm tested positive for H5N1.
Lisa Santora, public health officer for Marin County, said Wednesday that it appears the family was not aware when they purchased the milk and gave it to the child that it was unpasteurized. The milk from cows infected with H5N1 contains high levels of the virus, but studies have shown that commercial pasteurization kills the virus.
When a family member informed the doctor caring for the child about the consumption of raw milk, a flu test was ordered. An initial test, which involved swirling a cotton swab around the child’s nostrils, was negative, but a second was ordered a day later. That test, which involved rubbing a cotton swab around the child’s mouth and throat, tested positive for influenza A. That was the only test in this study that was positive for influenza.
Santora said the child’s relatives were also tested for flu, but all were negative. The child, who had no classic flu symptoms, has since recovered.
Scientists studying H5N1 are concerned about what could happen to people who drink unpasteurized milk containing the virus, based on evidence from some animals. Cats on farms where infected cows have died from drinking raw milk; A study earlier this year found that mice fed infected raw milk became so sick that they had to be euthanized.
Last month, a child in Alameda County, California, tested positive for H5N1. It has not been established how the child, who only had mild complaints, became infected with the virus.
California is currently the epicenter of the H5N1 outbreak in dairy cows. More than 600 herds have tested positive for the virus since the spread was first discovered there 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.