A study conducted in Iran and published in the October 1st edition of Clinical Infectious Diseases, has found that 11% of patients with multi-drug resistant tuberculosis were infected with a strain of the bacterium that was resistant to every single second-line anti-tuberculosis drug - so-called extensively drug-resistant TB (XDR-TB). The investigators also found that the XDR-TB identified in Iran was transmitted to individuals in two family and community clusters and that HIV-positive individuals were involved in these transmission clusters.
Tuberculosis is a serious public health concern in many countries around the world, and the incidence of the infection in Iran is 28 cases per 100,000 of the population. The tuberculosis problem has been made worse in many countries, Iran included, by the emergence of multi-drug resistant tuberculosis (MDR-TB), which is defined as tuberculosis that is resistant to the key first-line drugs, isoniazid and rifampicin.
MDR-TB can still be treated, but the duration of treatment is longer, involving less effective and more costly drugs. In recent years, however, there have been worrying reports of the emergence of strains of tuberculosis that are resistant to second-line drugs as well. As reported on aidsmap earlier this month, so-called XDR-TB has been found in 28 hospitals in South Africa and is rapidly fatal.
Iranian investigators analysed sputum samples from 2,030 tuberculosis patients between 2003 and 2005. Of these samples, 1,284 yielded positive cultures. A total of 150 (12%) of these showed evidence of multi-drug resistance. The investigators were able to perform further drug sensitivity testing on 113 of these samples and twelve (11%) of these were found to have evidence of resistance to all eight drugs available for second-line tuberculosis therapy.
None of the eleven patients with untreatable tuberculosis developed XDR-TB due to suboptimal therapy or poor adherence. Rather, every case involved transmission from another individual. Two transmission clusters based around extended family groups were identified by the investigators. Three of the patients in one of the clusters were HIV-positive.
The investigators were extremely concerned by the identification of XDR-TB, writing that the cases, “not only constitute a deadly threat to the affected patients with TB, but also hamper TB control programmes.”
In Iran a variety of second-line anti-tuberculosis drugs are used in a “poorly controlled manner” and the investigators believe that this caused the emergence of such extensively drug-resistant tuberculosis.
Effective tuberculosis control programmes and robust sensitivity testing of sputum samples to detect resistance to first and second-line therapies are needed, conclude the investigators.
Masjedi MR et al. Extensively drug-resistance tuberculosis: 2 years surveillance in Iran. Clin Infect Dis 841 – 847, 2006.