Officials at the U.S. Centers for Disease Control and Prevention (CDC) said today serology testing has ruled out H5 avian influenza infection in five health care workers who were showing symptoms at the time they were exposed to a patient in Missouri had, although the results suggest that a household contact was probably infected at the same time.
At a Department of Health and Human Services press conference today, CDC officials also said that testing had confirmed H5 infection in two poultry slaughterers in Washington, although the virus was genotype D.1.1, which is different from the genotype B3.13 that circulates in US dairy cattle.
Household contact in Missouri likely exposed to same source
Demetre Daskalakis, MD, MPH, who directs the CDC’s National Center for Immunization and Respiratory Diseases, said the CDC faces challenges with serology testing to assess whether symptomatic health care workers were exposed to a previously confirmed hospitalized patient in Missouri, along with a household contact of the patient, had also been infected with the virus. For example, the patient’s sample did not contain all of the virus’s sequences, and CDC scientists had to reverse engineer it to develop serology tests.
Tests on blood samples from all five health workers were negative on all serology tests, ruling out person-to-person transmission in the hospital setting, Daskalakis said. The CDC also detailed the findings in a spotlight on its website today. A sixth health worker had respiratory symptoms but tested negative for H5, so the patient did not undergo serology testing.
The results of the battery of three serology tests showed that the patient’s household contact, who became ill with gastrointestinal symptoms on the same day as the patient, was likely exposed to the virus but did not meet the criteria to be counted as a human H5N1 case. Both the patient and the household contact tested positive in one microneutralization test, but not in the other two tests. In previous testing, the patient’s respiratory sample was positive in the polymerase chain reaction (PCR) test.
Daskalakis said the identical outbreaks of illness from the patient and household contact suggested exposure to an unknown animal source or product rather than person-to-person transmission.
Washington cases confirmed but do not involve bovine genotype
Meanwhile, Nirav Shah, MD, JD, the CDC’s principal deputy director, said CDC testing confirmed H5 in two of the four presumptive positive results from poultry slaughterers in Washington state. He added that further testing is underway on at least five other presumptive positive results from the state.
The cases, the first in Washington, were announced by state health officials on Oct. 20. The workers were part of a team that culled poultry after a large outbreak at a laying hen farm in Franklin County. Shah said the two patients with confirmed infections had mild respiratory symptoms and conjunctivitis.
He said the genotype was D1.1 and belonged to group 2.3.4.4b, which circulates in wild birds worldwide and occasionally spreads to poultry populations. Although the D1.1 genotype is different from the B1.13 virus circulating in U.S. dairy cattle, it causes similarly mild symptoms, including conjunctivitis.
He praised Washington state for its good public health preparedness and said health officials had been conducting drills to prepare for outbreaks in animals and the arrival of cases in humans. Nirav said health authorities were in the middle of such an exercise in the region, where the poultry outbreak occurred on the same day the first human cases were detected. “Some thought it was an injection into the exercise,” he said.
Currently, the nationwide total number of H5 infections this year stands at 31 cases, and Shah said these cases are expected to increase as more confirmatory testing is completed. Washington health officials had also said they expected an increase in the number of confirmed cases as state testing identified more suspected cases.
Health officials said the risk to the general public remains low, but is higher for people who have professional contact with sick animals.
More positive herds in California and Idaho; Utah introduces tank testing for bulk milk
The United States Department of Agriculture’s (USDA) Animal and Plant Health Inspection Service (APHIS) confirmed three additional outbreaks in California dairy herds, bringing the total to 137, and two more in Idaho, bringing the state’s total to 36. To date, testing has confirmed bird flu in 339 dairy herds in 14 states.
Meanwhile, the Utah Department of Agriculture and Food (UDAF) yesterday announced mandatory weekly tank sampling for all dairy herds in Cache County after a large outbreak was confirmed at a Cache County layer farm with more than 1.8 million birds.
“Genetic sequencing has confirmed that the HPAI-H5N1 virus recently discovered at a commercial poultry farm in Cache County is the same virus that has affected dairy cattle in other states,” the UDAF said. “There are currently no confirmed cases of HPAI [highly pathogenic avian influenza] at dairies in Utah.”
A positive milk tank sample would trigger quarantine of the dairy herd and movement restrictions for lactating cows, except for those going directly to slaughter, the UDAF said.