Following an outbreak of Mycobacterium xenopi spondylodiscitis among patients who underwent surgery for a herniated disc at the Clinique du Sport (CdS) and based on recommendations from a group of experts, the Director General of Health (DGS) advised patients who underwent surgery for a herniated disc at the CdS between January 1988 and June 1993 to be screened for hepatitis B (HBV) and C (HCV) and human immunodeficiency virus (HIV) infection. The DGS asked the French Institute for Public Health Surveillance (INVS) to conduct a follow-up investigation of the screening and to assess the potential risk of HBV, HCV, and HIV transmission during herniated disc surgery at the Clinique du Sport during the period when deficiencies in medical equipment sterilization procedures had been identified. The investigation was conducted during the first half of 1999. A questionnaire was sent to patients considered to be at risk: those who had undergone percutaneous nucleotomy, microsurgical discectomy, or surgery for a herniated disc (without specifying the nature of the procedure) at the Clinique du Sport between January 1, 1988, and May 31, 1993. A follow-up was sent to non-respondents. Of the 3,062 exposed patients, 1,688 (55.1%) responded to the initial letter or the follow-up. The survey results indicate no excess risk for HIV and HBV. For HIV, 4 (0.25%) HIV-positive patients were identified, a prevalence similar to that observed in the general population. The HIV-positive status of the 4 patients was known prior to the CdS procedure. For hepatitis B, 7 (0.5%) patients were found to be HBsAg carriers. This prevalence is slightly higher than that found among patients eligible for autologous transfusion in mainland France and the French overseas departments in 1995 and 1996 (0.4% after adjustment for age and sex), but the difference is not statistically significant. For HCV, 23 (1.4%) seropositive patients were identified. This number is higher than expected when compared to two different reference populations. An excess of 11 cases is observed when compared to a population of patients eligible for autologous transfusion, and an excess of 7 cases, for the 20–59 age group, when compared to a sample of social security beneficiaries. The excess of cases is observed primarily among men aged 40 to 49 and among women aged 50 to 59. No association was found between HCV infection and the year of surgery, the type of open-heart surgery, or a specific surgeon. No single operating day with more than one patient infected with any of the three viruses was observed. No seroconversion for any of the three viruses was documented following a laparoscopic procedure. In conclusion, the analysis of epidemiological data does not support HCV transmission via medical-surgical equipment used and inadequately sterilized among patients in the same operating session. However, the study indicates that, among the patients who participated in the survey, the number of patients carrying the hepatitis C virus was higher than what was observed in two reference populations. A selection bias and the fact that the population of patients operated on at the Sports Clinic is likely not comparable to the reference populations in terms of risk factors for HCV infection partly or entirely explain the higher prevalence of HCV infection observed in the sample of respondents. Based on these conclusions, further investigation is not recommended. It is recommended that the results be communicated to patients via a personal letter prior to any public release of the results. (R.A.)