CDC, FDA, USDA answer big questions about the growing bird flu outbreak

The agencies are continuing to test milk, dairy products and meat to ensure they can not spread the virus, and working to monitor farm workers for more human cases of bird flu.

Here's a look at some of the questions they addressed.

Q: Has the virus spread between people?

A: While there can be rare instances of human-to-human transmission of bird flu, there have been no such cases in the United States. Dr. Rosemary Sifford, chief veterinary officer for the USDA, said researchers are not seeing changes in the virus that would indicate it might spread more easily between people. The dairy worker reported with bird flu on April 1 is the second human case of the virus reported in the U.S. The worker had conjunctivitis, a mild eye infection, and recovered.

Q: What is the CDC doing to respond to the bird flu outbreak?

A: Dr. Demetre Daskalakis, director of the CDC's National Center for Immunization and Respiratory Diseases, said the agency is looking for unusual trends in flu-like illnesses around the country and conjunctivitis—especially in areas where H5N1 virus has been found in dairy cattle or other animals. CDC's flu surveillance systems are not showing any signs of unusual flu activity, which might indicate avian influenza.

The CDC is also supporting the monitoring of exposed workers, Daskalakis said. People who have been exposed to infected cows, poultry or other animals are monitored for 10 days and if they show symptoms of illness, they are then tested. So far over 100 farm workers have been monitored.

He said the CDC is also providing guidance for farm worker protection, which includes a graphic for recommending personal protective equipment for those who work with farm animals and that is available in English and Spanish.

He said the agency is also conducting ongoing lab work, which includes genetic sequencing. Because viruses are constantly changing, he said the CDC is continually analyzing the virus to identify any genetic changes that suggest these viruses might spread more easily to and between people or might change in a way that makes antivirals and vaccines less effective.

Q: How is the virus spreading among dairy cows?

A: Dr. Rosemary Sifford, chief veterinary officer for the USDA, said studies indicate the recent infections of dairy cattle in the U.S. was the result of one "spillover event" from wild birds, and that they are not finding more than that single event.

That first spillover from birds to cows occurred in Texas and took place among a number of herds, she said. Once infected cows from those herds were moved to other states, the infection spread. As of Wednesday, 36 U.S. herds in nine states had confirmed infections, according to the U.S. Agriculture Department.

Sifford said the movement of cattle spreads the virus, but she also noted it can also spread through farming equipment. She said farmers with affected herds have reported about 10% of their herds displayed symptoms.

She said these cattle with symptoms "generally" returned to near their previous milk production levels after recovering from the virus, which is taking about two weeks. She said most cows are recovering with "little or no associated mortality."

Q: What dairy products have been tested for bird flu and where they purchased?

Last week, the FDA announced it had done testing on 96 commercially available milk products and found genetic traces in one of five samples, but that early data showed no live virus. Donald A. Prater, acting director of the Center for Food Safety and Applied Nutrition at the FDA, said the agency had done testing of an additional 201 products, which include cottage cheese and sour cream in addition to milk, and early data found none of the samples had "viable virus."

Several samples of powdered infant formula were also tested and the results from these tests were also negative.

Federal agencies expressed more concern about the possible dangers of drinking raw milk, and they once again urged people to not drink raw milk or eat raw cheese.

Q: What treatments are available?

There are four commercially available FDA-approved prescription antiviral treatment drugs recommended for influenza that are effective against H5N1, according to the CDC.

When reporters pressed CDC's Daskalakis about farm workers being given the antiviral medication Tamiflu "prophylactically," to protect them from illness, he said for the workers being offered this, it's a clinical decision made on a case-by-case basis.