Evidence of exogenous reinfection and mixed infection with more than one strain of Mycobacterium tuberculosis among Spanish HIV-infected inmates.

Background: As prisons have a high prevalence of tuberculosis and HIV infection, we studied the possibility of multiple tuberculosis infections in a selected population of HIV-infected inmates.
Methods: Two groups of patients with special characteristics were selected from 226 HIV-infected inmates diagnosed with tuberculosis in the prisons of Madrid (Spain) between 1993 and 1994. The first group contained nine patients who remained culture positive 4 months after the initiation of therapy and the second group contained 28 patients with Mycobacterium tuberculosis isolated from different anatomical sites. DNA typing with IS6110 was performed on all isolates from these patients. In some patients a secondary DNA typing with the plasmid pTBN12 was performed.
Results: Two patients from group A had a second M. tuberculosis strain obtained 4 and 18 months after the initial isolate, with different IS6110 and pTBN12 patterns. In one patient the second strain was multidrug resistant and in the other patient both strains had the same drug-susceptible pattern. The clinical and microbiologic evidence in both patients was consistent with the presence of active tuberculosis caused by a new strain of M. tuberculosis. In group B, the isolates from 27 patients shared similar fingerprint pattern; however, in one patient isolates from sputum and urine showed different IS6110 and pTBN12 patterns, although both strains showed the same drug-susceptible phenotype.
Conclusion: This study provides evidence that HIV-infected inmates living under conditions of high environmental infectivity can be infected with two different strains of M. tuberculosis. This finding has implications for the tuberculosis-control programs in prison.