By Tom Polansek and Leah Douglas
CHICAGO (Reuters) - Colorado began requiring dairies to test milk supplies for bird flu every week, the state's veterinarian told Reuters on Tuesday, as a federal team arrived to help investigate an escalating outbreak in cows that has spread to chickens and people.
The state's new mandate aims to identify additional farms that could be infected and spread the disease to other dairies or poultry flocks, after the largest cluster of human cases to date in the United States occurred on a Colorado farm this month.
Bird flu infections linked to dairy cows have wiped out 3.1 million egg-laying chickens in Colorado in recent weeks, and poultry workers also tested positive.
Colorado has confirmed infections in 47 dairy herds since the U.S. outbreak in cows began in late March, with about 60% of its cases detected in the past month, according to U.S. data. Nationally, 13 states have reported infections in about 168 herds since spring.
In Colorado, the loss of millions of chickens triggered the requirement for licensed dairies with lactating cows to test bulk milk supplies weekly, state veterinarian Maggie Baldwin said in an interview. About 70% of the state's laying hens were eliminated, according to U.S. data.
"We really said what we're doing right now is not effective and we need to change strategy," Baldwin said.
The U.S. Department of Agriculture since late April has required testing for lactating cows that are being shipped over state lines. The agency later launched a voluntary program to test bulk milk supplies.
A USDA epidemiological "strike team" arrived in Colorado this week to assess how the virus may be spreading among dairies there, Baldwin said. Workers or vehicles can carry the virus from farms.
If mandated testing reveals additional infections, Colorado can take further steps to contain the virus, Baldwin said.
Six Colorado farm workers tested positive for bird flu in July after culling chickens at an infected egg farm, the U.S. Centers for Disease Control and Prevention said.
More than 150 workers were exposed to the infected poultry, and 69 developed symptoms and were tested, according to the Colorado Department of Public Health and the Environment.
Colorado's public health department reported a presumptive positive human case on a different Colorado poultry farm on Friday. About 350 people were involved in culling chickens at that farm, where 23 workers developed symptoms and were tested, the department told Reuters. The CDC has not confirmed the presumptive positive case.
Testing remains in progress, Colorado's health department said on Tuesday.