HIV-seropositive patients respond to rifampicin-containing anti tuberculosis (TB) regimens as well as HIV-seronegative patients. In Nairobi, Kenya, 90% of HIV-positive patients who suffered a recurrence of TB first received a non-rifampicin-containing regimen. The overall unadjusted recurrence rate for HIV-positive patients was 16.7% while it was .5% for HIV-seronegative patients. An earlier, similar study in Zaire also showed a higher recurrence rate in HIV positive patients. A study in the US found a low recurrence rate among HIV-positive patients on rifampicin-containing regimens. A possible explanation for the higher recurrence rates may be that the thiacetazone-containing regimen is not as potent as the rifampicin containing regimen. Another possible explanation may be that no one knows the optimum duration of therapy for HIV-infected patients. 70% of HIV-positive patients in nairobi who suffered a recurrence of TB experienced a cutaneous-hypersensitivity reaction, resulting in a change in therapy and maybe affecting compliance. The researchers of the Nairobi study used DNA fingerprinting to determine whether the patients truly relapsed or were reinfected (cultures were available from only 3 HIV-positive patients). 1 patient was reinfected by a different strain of Mycobacterium tuberculosis. 4 of 17 AIDS patients in New York City were reinfected with a different multidrug resistant strain of M. tuberculosis. Reinfection is more likely to happen in sub-Saharan Africa where TB an HIV are very prevalent. Physicians cannot accurately determine a treatment regimen in HIV-infected patients in an area of high prevalence of TB. Thus, we need to determine reinfection rates in HIV infected patients to plan a response.