The increasing prevalence of infection with drug-resistant Mycobacterium tuberculosis represents a global public health emergency: At any given time, about 630 000 people in the world are thought to carry strains of M. tuberculosis showing resistance to the two drugs that are currently the most effective against tuberculosis (TB): isoniazid and rifampicin. (1) So far, the magnitude of the problem posed by multidrug-resistant TB (MDR-TB) has been estimated in about two thirds of all countries worldwide through disease surveillance and surveys. Each year, as more studies are conducted, new hot spots of MDR-TB are documented. (2) Among the countries that have been most severely affected by MDR-TB are several that formerly lay within the Soviet Union, including Belarus.
In 2006, Belarus established a national TB control programme and introduced international standards for TB care. (3) Patients in Belarus who are newly diagnosed with TB receive 2 months of treatment with isoniazid, rifampicin, pyrazinamide and ethambutol followed by 4 months of treatment with just isoniazid and rifampicin. An 8-month regimen is used for patients with a previous history of TB treatment. In addition to the isoniazid, rifampicin, pyrazinamide and ethambutol given to new cases, this longer regimen includes streptomycin (given for 2 months) and ethambutol (given for 8 months). (4) All TB patients undergo drug-susceptibility testing at the time of diagnosis and are switched to a standardized regimen containing the appropriate second-line drugs if MDR-TB is detected.
In recent years, the annual incidence of TB in Belarus has been slowly but progressively falling: 84 and 70 new cases were recorded per 100 000 population in 2000 and 2011, respectively. (1) However, the high prevalence of MDR-TB among TB patients in Belarus has raised major concerns. In a survey conducted in 2010 in Minsk, the capital city, nearly one out of every two (47.8%) TB patients investigated was found to have MDR-TB; this was the highest prevalence of MDR-TB ever recorded among TB patients worldwide. (5) The Minsk survey was, however, relatively small and limited to a highly urbanized area. The national Ministry of Health therefore decided to conduct a larger, nationwide survey, not only to have a better understanding of the levels of drug resistance throughout Belarus but also to investigate the risk factors for the development of MDR-TB. In this paper we report the results of the first national survey of drug resistance to be conducted among TB cases in Belarus and present an analysis of the data collected, during the same survey, on sociobehavioural risk factors for the development of MDR-TB.
The sampling frame consisted of patients who had pulmonary, smear-positive TB in any of the 196 health-care facilities in Belarus where TB can be diagnosed by the direct microscopical examination of sputum. In line with the guidelines of the World Health Organization (WHO), given that the frequencies of drug resistance among smear-positive and smear-negative cases of TB are similar, smear-negative cases were excluded from the study to avoid an excessive workload in the laboratories where M. tuberculosis isolates were to be cultured and tested. (6) For the same reason, patients with extrapulmonary disease were also excluded from the survey. The target sample sizes for new and previously treated TB cases were calculated using the notification data for 2009. For example, the target sample size for new cases was set at 927 on the basis of the number of new sputum-smear-positive cases of pulmonary TB reported in the country in 2009 (n = 1201), an expected prevalence of MDR-TB among new cases of TB of 20%, a predicted inability to test 10% of the collected samples (for reasons such as culture loss or failure), and a precision, for the 95% confidence intervals (CIs), of [+ or -] 1.5%. Similarly, the target sample size for patients with previously treated TB was set at 396 on the basis of the number of sputum-smear-positive cases of pulmonary TB reported in the country in 2009 (n = 878), an expected prevalence of MDR-TB among the previously treated cases of 60%, a predicted inability to test 10% of the collected samples, and a precision, for the 95% CI, of [+ or -] 4. …