Effectiveness of infection control measures in controlling a nosocomial outbreak of multidrug-resistant tuberculosis among HIV patients in Italy

SETTING: Between October 1992 and February 1994, 33 cases of multidrug-resi stant tuberculosis (MDR-TB) were diagnosed among patients infected by the h uman immunodeficiency virus (HIV) and hospitalised in an HIV ward in Milan, Italy. This outbreak was part of a much larger outbreak, begun in another hospital and probably transferred through a patient. OBJECTIVE: TO evaluate risk factors for transmission and the effectiveness of infection control measures. DESIGN: 1) Active follow-up of exposed patients, 2) cohort study among HIV- infected patients exposed to MDR-TB cases before and after the implementati on of control measures, 3) screening of close contacts of MDR-TB cases, and 1) molecular typing by restriction fragment length polymorphism (RFLP) ana lysis. RESULTS: The risk of MDR-TB was higher in patients with lower CD4+ lymphocy te percentages and longer duration of exposure. No difference in the daily risk was observed for in-patients vs day-hospital patients or by room dista nce from an infectious case. Of the 90 patients exposed before the implemen tation of infection control measures (i,e,, October 1992-June 1993) 26 (28. 9%) developed MDR-TB, whereas none of the 44 patients exclusively exposed a fter implementation developed MDR-TB, despite the continuing presence of in fectious MDR-TB cases in the ward. CONCLUSION: Simple control measures were effective in significantly reducin g nosocomial transmission among patients.