E. Bouvet et al., A NOSOCOMIAL OUTBREAK OF MULTIDRUG-RESISTANT MYCOBACTERIUM-BOVIS AMONG HIV-INFECTED PATIENTS - A CASE-CONTROL STUDY, AIDS, 7(11), 1993, pp. 1453-1460
Objective: To identify risk factors in a nosocomial outbreak of multid
rug-resistant Mycobacterium bovis (MDRMB) tuberculosis (TB) among HIV-
infected patients. Design: We evaluated the study period (from the fir
st to the last MDRMB smear-positive patients hospitalized in the unit)
using a case-control study with three control groups. Since MDRMB is
extremely rare, we assumed that a single strain was responsible for al
l six cases. Setting: A 19-bed infectious diseases unit in Paris, Fran
ce. Patients: The index case was an AIDS patient who was hospitalized
in September 1989 because of MDRMB TB. The cases were five HIV-infecte
d patients who developed MDRMB TB between January 1990 and October 199
1. Controls were randomly selected from HIV-infected patients in our u
nit during the study period (case-control study 1 , 15 patients), duri
ng the contact period (at least one MDRMB smear-positive patient hospi
talized in the unit; case-control study 2, 20 patients), and patients
matched according to the length of contact (case-control study 3, 24 p
atients). Interventions: After detecting the nosocomial outbreak, we t
ook respiratory isolation precautions for all patients suspected of ha
ving active TB. Main outcome measures: Risk factors for MDRMB nosocomi
al transmission, and the occurrence of new cases of MDRMB infection in
HIV-infected patients and health-care workers after the introduction
of isolation precautions. Results: The most important predictor of nos
ocomial transmission of MDRMB to HIV-infected patients was the (mean+/
- s.d.) length of contact in days [cases, 22+/- 15.8; study 1 controls
, 11.2+/- 18.9 (P=0.07); study 2 controls, 14.6+/- 8.5 (P=0.043)]. Onl
y one case of MDRMB TB resulted from exposure to MDRMB-smear-positive
patient after the introduction of respiratory isolation measures. The
incubation period in the single health-care worker who developed MDRMB
TB was longer than in the cases. Conclusion: In a nosocomial outbreak
of MDRMB TB, the contact time was the main risk factor of transmissio
n to HIV-infected patients. Respiratory isolation measures appear to b
e effective.