title: The influence of intravenous drug use and HIV infection in the transmission of tuberculosis.
abstract: OBJECTIVE
  To investigate whether smear-positive pulmonary tuberculosis (TB) patients present a different risk of TB transmission according to their HIV status, in an area where the majority of HIV-infected patients studied were intravenous drug users (IVDU).
  
  
  METHODS
  A case-control study was performed on smear-positive pulmonary TB patients diagnosed between 1990 and 1993 for whom a contact study had been performed. Patients with and without HIV infection were matched by age (+/- 3 years), sex and hospital of diagnosis. A micro-epidemic was defined if two or more secondary cases were detected from the same index case. Data were analysed comparing the percentage of contacts with TB in both groups.
  
  
  RESULTS
  Thirty-six secondary cases were detected in 436 contacts of 124 HIV-infected TB patients, whereas only 24 were identified in 624 contacts of 124 HIV-seronegative TB patients [odds ratio (OR), 2.14; 95% confidence interval (CI), 1.22-3.77; P = 0.004]. Comparing the contacts of HIV-infected patients, 34 secondary cases of TB were detected in 371 contacts of 97 IVDU, whereas only two cases were detected in 85 contacts of 27 non-IVDU (OR, 4.19; 95% CI, 1.09-15.95). HIV-seropositive index cases were observed to cause more micro-epidemics than seronegative cases (eight versus four), indicating that micro-epidemic cases were more frequent in the contacts of HIV-infected subjects (27 out of 36 versus 10 out of 24; OR, 1.41; 95% CI, 1.41-12.49; P = 0.009). All index cases in eight micro-epidemics were HIV-seropositive IVDU, whereas only four micro-epidemics were generated by HIV-seronegative subjects, none of whom were IVDU.
  
  
  CONCLUSIONS
  Smear-positive pulmonary TB patients were more likely to transmit TB if they were HIV-infected, as evidenced by the role of IVDU in generating micro-epidemics.
authors.affiliation: Epidemiology Service, Municipal Institute of Health, Barcelona, Spain.
authors.forename: J A
authors.initials: JA
authors.lastname: Caylà
authors.forename: P
authors.initials: P
authors.lastname: García de Olalla
authors.forename: H
authors.initials: H
authors.lastname: Galdós-Tangüis
authors.forename: R
authors.initials: R
authors.lastname: Vidal
authors.forename: J L
authors.initials: JL
authors.lastname: López-Colomés
authors.forename: J M
authors.initials: JM
authors.lastname: Gatell
authors.forename: J M
authors.initials: JM
authors.lastname: Jansà
mesh_terms: D000328:Adult; D016022:Case-Control Studies; D015897:Comorbidity; D004196:Disease Outbreaks; D005260:Female; D015658:HIV Infections / Q000150:complications*; D006801:Humans; D008297:Male; D012307:Risk Factors; D015819:Substance Abuse, Intravenous; D014397:Tuberculosis, Pulmonary / Q000150:complications / Q000175:diagnosis / Q000453:epidemiology / Q000635:transmission*