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Additional preliminary testing by the FDA has found that retail milk products such as cottage cheese and sour cream don't contain any viable H5N1 avian influenza virus, officials said during a press briefing.

Results from 96 products found retail milk samples didn't have any viable virus, and these additional results from 201 retail milk products showed no viable virus, either, Donald Prater, DVM, acting director of FDA's Center for Food Safety and Applied Nutrition, said during the briefing.

The agency also tested retail powdered infant formula and powdered milk products marketed as toddler formula, and there were no viral fragments on PCR testing, so additional testing for culturable virus weren't necessary, Prater said.

"These additional preliminary results further affirm the safety of the U.S. commercial milk supply," Prater said, adding that the agency is "continuing to identify additional products that we may test."

He reiterated the agency's stark warning against consuming raw milk and raw milk products: "We continue to strongly advise against the consumption of ... milk that has not been pasteurized, and recommend that industry does not manufacture or sell raw milk or raw milk products made with milk from cows showing symptoms of illness, including those infected with avian influenza viruses or exposed to those infected with avian influenza viruses," he said.

Last week, the agency announced on a that preliminary results from analysis of the 96 retail milk samples found one in five had viral fragments of H5N1, and the preponderance of these samples came from areas with known infections among dairy cattle herds.

The agency also previously reported that there was no culturable virus in that batch of samples.

Demetre Daskalakis, MD, MPH, director of CDC's National Center for Immunization and Respiratory Diseases, said more than 100 people have been monitored for symptoms and about 25 have been tested. Still only one person has tested positive for H5N1 during this outbreak among dairy cattle.

Daskalakis did not know how many people exposed to infected cattle reported having conjunctivitis.

He added that the agency developed for various groups of workers, which was recently expanded to people who work in slaughterhouses.

The agency also developed interim guidance for potentially exposed to the virus, as well as for .

Two existing H5 candidate vaccine viruses tailored to the strain involved in the current outbreak, 2.3.4.4b, are available to manufacturers and can be used to make vaccine if needed, Daskalakis said. A representative from the HHS Administration for Strategic Preparedness and Response said one of those candidate vaccines is now in early clinical trials, being evaluated for safety and immunogenicity by two manufacturers.

Available influenza antivirals also appear to work against the virus picked up from the Texas human case, Daskalakis said.

CDC plans to conduct serologic studies in farm workers but the agency is "waiting for the appropriate time and place to be able to launch them," he added.

Rosemary Sifford, DVM, chief veterinary officer at the U.S. Department of Agriculture (USDA), said there's no evidence of virus in any beef herds at this time.

José Emilio Esteban, PhD, under secretary for food safety at the USDA, said the agency is "confident the meat supply is safe," but is conducting three sampling efforts to be sure. Those include analysis of retail samples of ground beef; beef muscle samples from culled dairy cows; and cooking studies to ensure cooking would kill the virus should it exist in the meat.

"We're pretty sure that the meat supply is safe," he said. "We're doing this to enhance our scientific knowledge."

Sifford said evidence points to a single spillover event in the Texas panhandle, from wild birds into dairy cattle. Animals from those herds moving to herds in other states led to the initial movement of the virus, she said, adding that these animals being moved were asymptomatic.

Also, spread occurred through movement of equipment or other items between herds, she said.

The virus also moved from those cattle herds into other poultry flocks, Sifford said.

In the affected dairy herds, about 10% of the cows had symptoms, she said. These animals return to their previous levels of production after they recover, which takes about 2 weeks, she said. There's been little or no associated mortality, she added.

As of press time, have tested positive for H5N1.

"At this time, our focus is on identifying the currently affected herds and being able to work with them to eradicate the virus from the herd," Sifford said. "But we do have plans to do some serologic testing to try to understand the overall scope, including previously infected herds."

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