HIV may impact on tuberculosis in three different ways.
Two ways of impact are direct. A tuberculous infection may progress to clinical manifest tuberculosis if HIV infection becomes superimposed. A tuberculous infection may progress directly to tuberculosis if it is acquired subsequent to HIV infection.
The indirect effect of HIV infection on the epidemiology of tuberculosis is an increase in the risk of tuberculous infection in the general population due to an excess of infectious tuberculosis cases in the community.
These three mechanisms how HIV may impact on the epidemiology of tuberculosis can be illustrated with this nosocomial outbreak.
While it cannot be proven that these are truly the three mechanisms, the history of the outbreak suggests so. A patient hospitalized for HIV-associated illness developed unrecognized tuberculosis during hospitalization. This is possibly the first mechanism: reactivation of a pre-existing tuberculous infection with progressive immunosuppression.
Within less than two months, 6 other patients with HIV infection on the same ward developed tuberculosis. This is most likely the second mechanism: direct progression from a recently acquired tuberculous infection to clinically manifest disease in a patient with pre-existing HIV infection.
Six months after occurrence of the index case, a health care worker without HIV infection developed tuberculosis. This is most likely the third mechanism: transmission of M. tuberculosis from any of these excess cases that would not have occurred without HIV to the general population.
If this happens in a hospital setting, this is likely to also occur in the community at large. |
