Health officials say hundreds of people may have been told they have syphilis when they don't.
The Centers for Disease Control and Prevention says a study of five U.S. labs shows about 18 percent of the positive results from a test method used since the 1980s were actually negative.
People who test positive for syphilis are usually given penicillin, which can have side effects for some people. The test is given to all pregnant women and people considered high-risk for sexually transmitted diseases.
It's not clear how widely used the problematic test is versus another method. The CDC recommends a second test when there's a positive result. Only about 14,000 Americans have the most contagious forms of syphilis.
© 2011 The Associated Press.