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Drug-resistant Tuberculosis

4. Why do HIV and tuberculosis form a lethal combination?

    HIV-TB patient in Thailand.
    HIV-TB patient in Thailand.
    Source: Thiery Falise

    Tuberculosis can be very difficult to detect in people who are HIV-positive. Tests to detect tuberculosis are often negative in people infected with both HIV and TB, which can cause delays in the diagnosis. In addition, people infected with dormant tuberculosis bacteria can quickly become sick with tuberculosis when their immune systems are weakened by HIV. This, together with the difficulty of treating both diseases at the same time, has led to high death rates in people living with TB and HIV.

    Tuberculosis is one of the opportunistic infections closely associated with HIV and there have been many outbreaks of drug-resistant forms of tuberculosis in places where large numbers of HIV-positive patients are in close contact with each other such as some hospitals and prisons. However, information on how tuberculosis is transmitted in these particular settings cannot be used to predict the spread of drug-resistant tuberculosis in the general population. This is an important point because people infected with both HIV and tuberculosis develop the disease quickly and, if they are infected with MDR-TB, they could start an outbreak of drug-resistant tuberculosis.

    There are two main reasons why HIV and drug-resistant tuberculosis may be associated: HIV infection or its treatment could result in poorer absorption of anti-tuberculosis drugs or in acquired resistance to these medicines. In addition, HIV-infected patients and drug-resistant tuberculosis patients may have similar risk factors such as history of hospitalization. It is also possible that HIV infected patients may be more susceptible to infection once exposed, although no data support this.

    The main obstacle to understanding the association between HIV and drug-resistant tuberculosis is the lack of data available. In Ukraine and Latvia, there is a high proportion of MDR-TB and an emerging HIV epidemic that is becoming more generalized in the population. The data gathered in these two countries will be crucial not only to find the right treatment for the patients, but also to help understand how HIV may affect the spread of drug-resistant tuberculosis in the region. The development of infection control measures as well as diagnostic screening tools to rapidly identify drug resistant TB are a priority, for all countries, but particularly for those with high prevalence of HIV or MDR-TB.

    From a global perspective, patients would benefit if tests for HIV and TB were carried out at the same time.

    Additional studies will be needed to understand the association between HIV and drug-resistant tuberculosis at the population level.

    This text is a summary of: WHO,  Anti-Tuberculosis Drug Resistance in the World, Fourth Global Report (2008), Chapter 4: Discussion, Drug resistance and HIV (p. 85-87)

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