BSE: Should you worry about these false positives?

SALEM, Ohio – After the first two inconclusive bovine spongiform encephalopathy (BSE) tests came back negative, speculation centers on how these ambiguous results will affect the public.

If there are as many inconclusive results as the USDA is implying, will people be desensitized? And should they be prepared for USDA announcing false positives often?

The University of Nebraska’s David Smith says yes.

After the first case of BSE was found in the United States in December, the USDA was criticized for not disclosing the incident sooner, said the veterinary scientist.

“USDA officials now want to be as transparent as possible,” Smith said, which means the department will announce all inconclusive test results.

In response to that first case of BSE in the United States, advanced surveillance began June 1, and approximately 9,000 cows have been tested for the brain-wasting disease.

The inconclusive tests were found June 25 and 29. The USDA’s National Veterinary Services Laboratories confirmed the cows did not have BSE within four days of each screening test.

Seriousness. The surveillance program is working, and the public needs to become more accustomed to the testing process and inconclusive results, Smith said.

It takes time for labs to learn to do the tests properly, and they will have more inconclusive results in the early testing period, said Ohio State livestock economist Brian Roe.

“Experience from other countries suggests that future positives generated by screening tests should be taken more seriously, not less seriously,” he said.

As labs grow accustomed to using these tests, they will get better at it and produce fewer false positives, Roe said.

“[This] increases the chance that a ‘positive’ during the screening phase is more likely to be a true positive,” he said.

Silent phone. The USDA and experts agree there will be many more false positives in the future, but are people worried?

Ohio State University beef veterinarian Bill Shulaw did numerous phone and television interviews after BSE was confirmed last year in Canada and then the United States, however, since the inconclusive results were released, he’s only had one phone call.

“In terms of the average consumer, BSE is probably not on the radar,” he said, noting that may change if a positive case was found.

Shulaw anticipates more of a response in the market.

Each time a false positive is reported, there is a ripple in the market, he said.

“It’s an exaggerated response because of fear,” he said. (For more information about the market’s response, see Will this summer’s cattle prices be a false positive? on page A8.)

Valued test. Colorado State University research agrees consumers may not be too worried about BSE.

Results proved consumer confidence in the food supply remained high this year, researchers found.

According to the study, only 22 percent of people changed their beef purchasing after the December BSE case. One-third said they eventually returned to their previous purchasing behavior.

“The survey also shows that consumers highly value BSE testing, which could suggest that increased testing may be cost effective in some consumers’ opinions,” said university economist Dawn Thilmany.

Never perfect. The initial rapid screening test for BSE, like any test, is never perfect, said University of Nebraska veterinary scientist David Steffen.

With this test, scientists typically expect less than 1 percent of results to be a false positive.

Steffen said this is expected because of the large number of cattle being screened.

“If there is a false positive for every thousand tests, then the USDA could expect hundreds of false positive reports from the 200,000 tests to be conducted by next June,” Smith added.

“The public and the markets need to be prepared for that.”

The screening test used in Japan, for example, has produced 118 inconclusive results, Roe said. Further testing confirmed only nine of them were BSE positive, he continued.

Comparisons. Ohio State’s Shulaw stresses the test is just for screening purposes.

“These tests aren’t perfectly discriminatory – clearly positive or clearly negative,” he said. “The screening test just identifies animals for further testing.”

He compares it to a woman checking for breast cancer. If during a self-examination she feels a lump, she does not automatically assume it is cancer, he said.

Instead she goes to a doctor who does further testing. The final determination of whether she has cancer does not come until the lump is removed and sent to a pathologist.

“We felt the ‘lump’ here in this cow,” he said, but it takes further tests to know if it is definite.

Related article: Will this summer’s cattle prices be a false positive?

(Reporter Kristy Hebert welcomes reader feedback by phone at 1-800-837-3419, ext. 23, or by e-mail at


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