The USDA was notified last week that an inconclusive BSE test result had been received on a rapid screening test used as part of the agency's enhanced BSE surveillance programme.
The agency has been at pains to stress that the inconclusive result does not mean another case of BSE in the US has been discovered. Inconclusive results, it says, are a normal component of screening tests, which are designed to be extremely sensitive.
Tissue samples have now been sent to the USDA's National Veterinary Services Laboratories at the national BSE reference lab, which will run confirmatory testing.
The USDA says that as the test is only an inconclusive test result, no specific details will be disclosed. In addition, the animal did not enter the food or feed chain.
Nonetheless, the USDAs' reaction to the inconclusive test shows how far BSE prevention has come. Internal steps to begin initial tracebacks, if further testing were to return a positive result, have already been initiated.
Confirmatory results are expected back within the next four to seven days. If the test comes back positive for BSE, the USDA says that it will provide additional information about the animal and its origin.
BSE remains a sensitive issue for consumers, policy makers and the beef industry. In late December 2003, the US identified a BSE infected cow in the state of Washington, leading to a ban from more than 20 countries on imports of US beef.
The after-effects are still being felt. Earlier this year, a Wall Street Journal Online/Harris Interactive Health-Care Poll in the US showed that one in every five American adults - 21 per cent - said that fear of mad cow disease would change their eating habits, while 78 per cent of these people said that they would eat less beef.
Some 16 per cent indicated that they would stop eating beef altogether.
However, the agency remains confident in the safety of the US beef supply. It says that the current ban on specified risk materials from the human food chain provides protection to public health, should another case of BSE ever be detected.
Measures to strengthen public health safeguards in the US include the longstanding ban on imports of live cattle, other ruminants, and most ruminant products from high-risk countries. In addition, non-ambulatory cattle have been banned from the human food chain and air-injection stunning of cattle has been made illegal.
And any animal presented for slaughter that has been sampled for BSE, will be held until the test results have been confirmed negative.
The global beef industry's worst fear is a rerun of the BSE crisis that gripped the UK in the late 1990s. Domestic sales of beef products declined immediately by 40 per cent following reports of a possible link between BSE and new variant CJD - a human form of BSE - in 1996. Export markets were completely lost.