On June 25, the USDA announced that a beef animal had an inconclusive result on the commonly used BSE screening test and that confirmatory follow-up testing would be conducted at the National Veterinary Services Laboratory in Ames, Iowa.
Less than a week later, the USDA announced a second animal with inconclusive test results. Again animal tissue was sent to Ames for confirmatory tests.
As I write this column, the confirmatory tests for both animals are in and they are negative.
In part because of the difficulty of keeping rumors of an inconclusive report from circulating in the trade and media, the USDA has adopted a policy of reporting all such incidents as they occur.
Some, like Randy Patterson, president of the Livestock Marketing Association, have argued against such announcements saying that “immediately after these announcements, the livestock futures market and the cash market have taken terrific beatings. And while these markets have rebounded, they never seem to recover to pre-announcement levels.”
Others like the National Cattlemen's Beef Association (NCBA) have argued in favor of the USDA policy. In a press release the NCBA says, “Reporting inconclusives as soon as they are known is intended to insure that everyone has the same information at the same time.”
Before weighing in on one side or the other of that argument, let us take a few moments to understand what is being reported and what is at stake.
In any disease testing procedure there are two possibilities: the animal being tested has the disease or it doesn't. Similarly, there are two possible test results: positive and negative.
If a disease-free animal tests negative, there is no problem. However if a diseased animal tests negative, we have what is called a “false negative.” Because of the seriousness of BSE in the public's eye, the testing goal is to minimize the possibility of a false negative test result because that would allow a diseased animal to enter the food chain.
The usual way of minimizing the chances of a false negative on a rapid test like the ELISA test now being used by USDA to detect BSE is to tighten the test tolerances. What happens when you do that is that some animals that are disease-free get flagged anyway. This is called a “false positive.” The two June animals fell into this false positive category.
What the USDA reports as “inconclusive” are in reality positive results on the preliminary screening test. These animals are then retested using a slower but more precise testing technology at the Ames Lab. If the second test shows that the disease is not present, the first report is called a false positive.
These procedures are similar to those used when people are tested for breast or prostate cancer. How many times have we breathed a sigh of relief when a neighbor's biopsy has come back negative after an earlier test showed the possibility of cancer?
I would suggest that USDA reporting initial inconclusive (positive) results is little different from the doctor telling you that a biopsy is needed to follow up on a mammogram. Yes, hearing the result of the first test does make us a little anxious, but most of us would rather know than not know.
It is a good guess that after a few more inconclusive reports, the market and the public in general will settle down and take the news in stride. While causing price fluctuations now, I believe that the USDA's decision to opt for openness in reporting is a good thing in the long run. Hopefully, it will build confidence in the USDA's handling of BSE and in its mission to protect the public from this disease.
Daryll E. Ray holds the Blasingame Chair of Excellence in Agricultural Policy, Institute of Agriculture, University of Tennessee, and is the director of UT's Agricultural Policy Analysis Center (APAC). e-mail: [email protected]. Ray's column is written with the research and assistance of Harwood D. Schaffer, research associate with APAC.