A word of caution: one should take into account the coverage of drug susceptibility testing when interpreting results Susan van den Hof, KNCV Tuberculosis Foundation 16 January 2013 We very much welcome the publication of results on tuberculosis epidemiology from Kazakhstan in BMC Infectious Diseases by researchers from within the country. It is important that insights from Kazakhstan and other Central Asian countries are shared with the international, non Russian speaking, community. Kazakhstan is a country with a declining incidence of tuberculosis, but with a high prevalence of multi-drug resistant tuberculosis (MDR-TB). It is therefore important to study and know the trends in the MDR-TB burden, and understand risk factors. As we find it an important field of research with important implications, we would like to comment on this manuscript. The authors state that the incidence of MDR-TB in Kazakhstan has increased in recent years, from 2007 to 2010. This statement is based on the number of diagnosed MDR-TB cases. We would like to point out that the increase as calculated by the authors is not statistically significant (P=0.12). More importantly however, one should realize that the coverage of drug susceptibility testing (DST) and its reporting in the TB register has increased during these years. Although all oblasts have been able to perform culture and DST for years and they have made tremendous progress in recent years, the actual coverage and reporting of results has not been and still is not complete. Increased DST coverage from 2007 onward may also partly explain the trends within oblasts presented in this article: in 2007 DST results were not included in the electronic TB register for 34% of all notified TB patients compared to 47% in 2010. In a study with a different focus but based on the same routine TB surveillance data from Kazakhstan over the years 2007-2011, and accepted for publication in the International Journal of Tuberculosis and Lung Disease (IJTLD), we show that overall MDR-TB prevalence among those with DST results available remains similar over these years. With a decreasing overall TB incidence, this means that the MDR-TB incidence rate in fact probably has gone down. While taking into account DST coverage, it would have been advisable to stratify the data by treatment history, as this is a main determinant for MDR-TB and could show trends in MDR-TB rates for new and retreatment patients separately. This is important as drug resistance among new TB patients is a marker for transmission of MDR-TB, while MDR-TB prevalence among retreatment patients at least in part is due to acquired resistance. Most of the patients (83-87%) did not have one of the predefined risk factors registered. The authors seem to interpret this as if these patients have an existent but unknown risk factor, which needs further research. However, especially in a TB endemic country, it is very well conceivable that many TB patients do not have one of the major risk factors for TB. From the methods and results presented, we are not confident about the statistical methods used. For instance, we are not sure whether and if yes, at which geographical level the notification rate of new TB was correlated to the proportion of patients with a certain risk factor. Also, the authors use variables in the analysis on risk factors that are not appropriate for this analysis. For instance, non-adherence occurs during treatment, after diagnosis, and thus could be used as a risk factor for unsuccessful treatment outcomes but is not a risk factor for the occurrence of new TB. KNCV Tuberculosis Foundation is an NGO founded in the Netherlands with a representative office in Almaty, Kazakhstan. Over the last years, we have provided technical assistance to national tuberculosis programs in Central Asia and as such also have gained knowledge and experience with the national electronic tuberculosis register in Kazakhstan. While we highly respect the efforts of the authors to share their insights with the international scientific community, we feel compelled to caution readers when interpreting the conclusions presented here. Kind regards, Susan van den Hof (1) Aigul Tursynbayeva (2) Svetlana Pak (2) 1. KNCV Tuberculosis Foundation, The Hague, The Netherlands 2. KNCV Tuberculosis Foundation, Representative office for Central Asia, Almaty, Kazakhstan Competing interests We declare not to have any competing interests.