BSE 'FALSE POSITIVES' PART OF NEW TESTS

WASHINGTON -- Retailers and the shopping public can anticipate more announcements of "inconclusive" initial test results for mad cow disease as the government's expanded carcass testing program hits full gear.The announcement that two carcasses -- tested within four days of one another -- returned inconclusive results is raising questions as to how the expanded testing program administered by the

WASHINGTON -- Retailers and the shopping public can anticipate more announcements of "inconclusive" initial test results for mad cow disease as the government's expanded carcass testing program hits full gear.

The announcement that two carcasses -- tested within four days of one another -- returned inconclusive results is raising questions as to how the expanded testing program administered by the U.S. Department of Agriculture works, and what information exactly is disclosed.

Officials later announced that subsequent, more sophisticated tests showed neither animal had been infected with the disease.

The agency plans to continue announcing inconclusive findings the same day they are received, on the Web site of the USDA's Animal Plant Health Inspection Service, along with a running list of negative results. However, the agency will identify any suspect cow, its origin or any other information about it only if a more sophisticated confirmation test comes back positive.

While that information is easily available, officials have been reluctant to estimate how many inconclusive test results might occur within the expanded test protocol, though J.B. Penn, USDA under secretary, had earlier been quoted as saying there could be one inconclusive result for every 10,000 tests performed.

"We prefer not to put any type of statistic on that," Dr. John Clifford, deputy administrator for APHIS, told participants during a recent teleconference on the matter.

"You can look at some of these tests and their use internationally, but I think we need to have that experience here with the U.S. and the population of animals that we're testing before we would prefer to give any type of statistical numbers," he said.

Clifford noted the one-in-10,000 number refers to the testing structure erected as part of the Japanese government's BSE monitoring program, which cannot accurately be used to gauge the U.S. results.

"The Japanese are testing a different class of animals than what we're testing, and we could see results that differ from what they're seeing," Clifford said.

Nevertheless, the USDA is testing more cattle for bovine spongiform encephalopathy, most recently processing results on nearly 3,000 head of cattle during a single week. Clifford said those numbers will continue to increase as the program is fully implemented.

"We began our expanded BSE surveillance program June 1, and if you look at the numbers on [a] weekly basis, you'll continue to see those numbers increase," he said. "And we would expect that [number of tested cattle] to increase for quite a bit of time."

The primary focus of the USDA's enhanced surveillance effort is on the highest-risk populations for the disease, and the expanded program greatly increases the number of target animals surveyed. It also includes a random sampling of apparently normal, aged animals. According to the agency, using the enhanced program to sample some 268,000 animals would allow for the detection of BSE at a rate of one positive for every 10 million adult cattle, with a 99% confidence level. In other words, the enhanced program could detect BSE even if there were only five positive animals in the entire country. Sampling some 201,000 animals would allow for the detection of BSE at the same rate at a 95% confidence level, officials said in an earlier news release detailing specifics of the expansion.

Right now, the sampling of apparently normal animals is coming from the 40 U.S. slaughter plants that handle 86% of the aged cattle processed for human consumption here each year.