Hundreds of people may have been told they tested positive for syphilis when they didn?t actually have the disease, health officials say. A study of five U.S. labs shows about 18% of the positive results from a test method used since the 1980s were actually negative, the Centers for Disease Control and Prevention said Thursday. Experts previously thought the statistic was much lower?under 7%. The CDC recommends additional testing when this particular test gives a positive result. But even if most doctors retest, the new research suggests that some people have unnecessarily worried they were infected with an infamous sexually transmitted disease.