An eagerly anticipated serology study in farm workers exposed to H5N1-infected dairy cattle shows that 7% had antibodies suggesting prior infection, findings that today triggered enhanced testing, prophylactic (preventive) treatment, and use of personal protective equipment (PPE) from the US Centers for Disease Control and Prevention (CDC).
The number of H5 avian flu infections in farm works continues a slow but steady rise. California yesterday reported one more infection in a dairy worker, and Washington state reported two more in poultry cullers. The cases boost the CDC's confirmed case total to 46.
Four of 8 who tested positive remembered symptoms
The serology study included blood samples collected from June to August from 115 farm workers who had been exposed to sick cows in Colorado and Michigan. The samples were collected between 15 and 90 days after exposure. CDC scientists and their state health partners detailed the findings today in Morbidity and Mortality Weekly Report (MMWR).
At a media briefing today, Demetre Daskalakis, MD, MPH, who directs the CDC's National Center for Immunization and Respiratory Diseases, said the serology testing involved a multistep protocol that was done to rule out cross-contamination from seasonal flu viruses. Of the 115 samples, 8 were positive for H5 avian influenza antibodies. He added that the 7% infection level isn't far from other recent seroprevalence studies for H5N1, such as in Egyptian market workers, which found a 4.6% level.
Dairy workers, all of whom spoke Spanish, were also interviewed about prior symptoms, the types of jobs they did on the farms, and the protective equipment they used, which Daskalakis said was done so that health officials can better understand the human infection dynamics on the farms.
Four of the workers said they remembered having symptoms, which included conjunctivitis. Tasks included milking cows and cleaning barns. None of the workers wore respiratory protection, and less than half used eye protection.
Only one of the workers reported working with cows known to be infected.
New testing, Tamiflu recommendations
Nirav Shah, MD, JD, the CDC's principal deputy director, said that, in light of the serology findings, the CDC is expanding recommendations on who should be tested to include workers who are exposed to sick cows or poultry but aren't experiencing symptoms. "We in public health need to cast a wider net," he said.
Active detection of cases can help reduce infections and illness severity in workers and reduce the risk of them spreading the virus to other people, Shah said.
Also, the CDC stepped up its recommendation for oseltamivir (Tamiflu) prophylaxis to include any asymptomatic worker with high-risk exposure, especially those who didn't wear adequate PPE. The step is geared toward preventing infections in workers and cutting the risk of onward spread.
Given the PPE findings, the CDC today adjusted its recommendations, focusing on the farm tasks that pose the highest risk, such as working in milking parlors and culling sick poultry. "This is an example of the CDC using data to drive actions," he said.
Shah said although the serology findings add evidence of undetected illnesses and an undercount of cases, the agency still doesn't have enough data to estimate the true number of infections in farm workers.
Inadequate PPE use on outbreak farms
In a related development, Colorado researchers who surveyed 83 dairy workers from three outbreak farms found that PPE was usually available, but wasn't always used, even when the virus was found in cows. They published their findings today in a separate MMWR report.
The most frequent activities were milking cows or working in the milking parlor, cleaning cow manure, and transporting animals.
The most common PPE available before outbreaks were identified included gloves at 88%, followed by eye protection at 76%, rubber boots at 71%, and head covers at 69%.
Though masks were used more frequently, N95 respirator use was low among workers who were exposed to cows after H5N1 was detected—only 26% reported wearing that form of protection. The team acknowledged that hot weather and humid conditions in milking parlors make it difficult and uncomfortable to wear respirators, posing obstacles to use, especially in the summer months. The authors said that messaging consistent with CDC PPE recommendations could encourage use of better respiratory protection.
Overall, PPE use jumped 28% after the virus was found in cows, especially eye protection, which rose 40%.
