On 2017 Feb 22, Tom Yates commented:

Shah and colleagues are to be congratulated for an important study (Shah NS, 2017), emphasising the major role of transmitted resistance in the epidemiology of extensively drug-resistant tuberculosis (XDR-TB). However, methodological issues will have impacted the results.

As the authors acknowledge, in such studies, missing data bias estimates, with linked isolates wrongly designated unique. Their decision to look at a convenience sample of 51% of cases from throughout KwaZulu-Natal rather than attempt complete enrolment in a smaller area will have accentuated this bias.

A growing body of research suggests transmission between members of the same household only explains a small proportion of all Mycobacterium tuberculosis (MTB) transmission in Sub Saharan Africa (Verver S, 2004, Andrews JR, 2014, Middelkoop K, 2015, Glynn JR, 2015). In the present study, recall bias plus disease prompting contacts to test for XDR-TB will likely have resulted in household, workplace and hospital contacts being captured more consistently than more casual community contacts.

Determining the proportion of total MTB transmission occurring in specific locations would allow disease control programmes to be better targeted. I agree with Shah et al that this should be a research priority.

Dr Tom A. Yates, Institute for Global Health, University College London, t.yates@ucl.ac.uk

On 2017 Feb 22, Tom Yates commented:

Shah and colleagues are to be congratulated for an important study (Shah NS, 2017), emphasising the major role of transmitted resistance in the epidemiology of extensively drug-resistant tuberculosis (XDR-TB). However, methodological issues will have impacted the results.

As the authors acknowledge, in such studies, missing data bias estimates, with linked isolates wrongly designated unique. Their decision to look at a convenience sample of 51% of cases from throughout KwaZulu-Natal rather than attempt complete enrolment in a smaller area will have accentuated this bias.

A growing body of research suggests transmission between members of the same household only explains a small proportion of all Mycobacterium tuberculosis (MTB) transmission in Sub Saharan Africa (Verver S, 2004, Andrews JR, 2014, Middelkoop K, 2015, Glynn JR, 2015). In the present study, recall bias plus disease prompting contacts to test for XDR-TB will likely have resulted in household, workplace and hospital contacts being captured more consistently than more casual community contacts.

Determining the proportion of total MTB transmission occurring in specific locations would allow disease control programmes to be better targeted. I agree with Shah et al that this should be a research priority.

Dr Tom A. Yates, Institute for Global Health, University College London, t.yates@ucl.ac.uk