Health officials in the US are to meet next month to decide whetherto recommend mandatory HIV tests for dentists and surgeons. The meetingfollows last week’s announcement by the federal Centers for Disease Controlthat a dentist in Florida had infected at least three of his patients. The case raises new questions about the risks of becoming infected withHIV during medical and dental treatment. Apart from the Florida cases, therehave been no confirmed reports of any doctor or dentist transmitting thevirus to a patient. Researchers admit that they are baffled by the cluster of infections,and they cannot be sure what the route of infection was. They suggest thatthe dentist could have cut or punctured one of his fingers while it wasin a patients mouth. Or he could have used a contaminated instrument. Butthere is no documented evidence of such events in the practice records. The researchers are convinced that the dentist was the source of theinfections because the virus samples are extremely closely related. Allthe patients denied having sex with the dentist or each other. ‘We believe that the risk of transmission (in medical and dental settings)is very small, said Harold Jaffe at the CDC’s devision of HIV and AIDS. ‘The Florida cases are odd. We know there are some surgeons and dentistsinfected with hepatitis B who have infected 20 or 30 of their patients,while others have infected none at all,’ said Jaffe. The concentration of virus in the blood could affect the risk, he said:the dentist’s disease ahd progressed to AIDS by the time he treated twoof the three so it is likely that his blood contained large amounts of HIV. David Acer, a dentist who has now died of AIDS, infected the patientsbetween 1984 and 1989. The case of patient A, a 22-year-old woman with noknown factors that would put her at risk of infection, was first reportedlast summer. After this, 591 other patients were tested for HIV. The tests revealed a second infected woman, patient B, who was elderlyand had no known risk factors, and a young man, patient C, who has had manyfemale sexual partners. None of his partners who have been traced are HIV-positive. Gerald Myers at the Los Alamos National Laboratory analysed the dataon the genetic sequences of the strains provided by the CDC. The virusestaken from the dentist, and patients A, B and C, varied from each otherby only 3.4 per cent in the highly variable sequence encoding the V3 loop,part of the virus’s protein coat. Such small variation is usually foundonly in different samples taken from the same patient or from individualswho are known to have infected each other.