California officials have ordered bulk milk testing at dairy farms within a six-mile radius of herds infected with H5N1 bird flu, as well as at dairies that share trucks, staff or equipment with facilities that have experienced an outbreak.
The mandatory testing comes as the total number of infected herds in California has risen to 17. Nationally, officials have announced 218 outbreaks in 18 states. However, in the past 30 days, California has recorded all but two outbreaks.
Authorities have not yet revealed the location of these herds, except to say they are somewhere in the Central Valley. They also say the country's supply of milk and dairy products is safe for consumption; pasteurization inactivates the virus.
When officials conduct mass testing, they examine the combined milk production of several cows on a farm. If the tests reveal the presence of the H5N1 virus, more precise testing is done to locate infected cows or subherds for isolation.
The state is quarantining all farms that are found to have H5N1 or that refuse to test. It is also quarantining dairy farms that are within six miles of an infected herd or that have contact with an infected herd.
“To date, all dairies have been cooperative,” said Steve Lyle, a spokesman for the California Department of Food and Agriculture. Authorities have the authority to require testing under state law, he said.
Testing is underway on nearly 100 farms, Lyle said.
In addition to the infections in the flock, an outbreak of H5N1 was also reported in a commercial turkey flock on September 18. The number of turkeys in the flock has not yet been disclosed.
Federal and state officials have released county-level data on infections in commercial poultry, but not livestock.
John Korslund, a retired U.S. Department of Agriculture veterinary epidemiologist who writes online about livestock diseases, fears California could soon find itself in a situation similar to Colorado's.
Between May and August, 64 Colorado flocks were infected, as well as six poultry workers.
Colorado has about 100 dairy herds and about 200,000 dairy cows. California has 1,300 dairy herds and about 1.7 million cows.
“The problems in California are just beginning,” Korslund said.
Wastewater testing by the Centers for Disease Control and Prevention and WastewaterScan, an infectious disease monitoring network, has detected the H5N1 virus in samples collected in Turlock and San Diego.
Health officials say they cannot identify the source of the H5N1 in the wastewater, saying it could have come from discarded milk or wild animals.
CDC and WastewaterScan test only at a few wastewater treatment sites in the Central Valley, including those in Placer, Yuba, El Dorado and Sacramento counties. However, there are only two sites further south in Merced and Stanislaus counties. There are no participating wastewater treatment sites in Fresno, Kings, Tulare, Kern, Madera or San Joaquin counties.
Ninety percent of the state's dairy cows are located in the San Joaquin Valley, which includes San Joaquin, Stanislaus, Merced, Kings, Madera, Fresno, Tulare and Kern counties. Thirty percent of the state's dairy farms are located in Tulare County.
