In our last blog we published the letter we wrote to Dr Matteo Zignol of the WHO in response to a letter which he wrote to the Guardian dismissing a study of MDR-TB prevalence in West Africa (conducted in eight countries) as being "unhelpful" and "misleading" without any real substantiation.
Given the fact that there is very clearly an MDR-TB problem in the region (indeed the estimated rate of MDR-TB in Nigeria rose 20% in a single year in the most recent WHO Global TB Repor) his letter disturbed us enough that we decided it would be right to publish our letter to him (which, of course we advised him of). He recently responded, our letter having somehow got lost at its first sending.
We publish his response in full below. It's not a response, unfortunately, which has satisfied our concerns although we very much appreciate his efforts to explain his original letter. Regrettably we still don't understand why he found the study to be so unhelpful and misleading - enough to have written to the Guardian newspaper. We have therefore responded explaining our continuing concerns. Meanwhile we publish his letter in full for your own assessment.
Dear Mr Young,
For some reasons I don’t seem to have a record of your previous message. Thanks for the reminder and sorry for the inconvenience.
I fully share your concerns re. the lack of data on the magnitude of the problem of drug-resistant tuberculosis in Western Africa.
The point I wanted to make with my letter is very simple: the conclusions put forward by the authors of the study and reported by the journal (” West African drug-resistance prevalence poses a previously underestimated, yet serious public health threat, and our estimates obtained differ significantly from previous World Health Organisation (WHO) estimates. Therefore, our data are reshaping current concepts and are essential in informing WHO and public health strategists to implement urgently needed surveillance and control interventions in West Africa.”) are not supported by the study design and therefore are misleading.
I think everyone understands that results of a study conducted in selected national TB referral centers cannot be extrapolated to entire countries. It is well known from evidence from all over the world that in hospital settings and health referral centres, levels of resistance to anti-tuberculosis drugs are significantly higher than those found in a nationally representative surveys of TB patients. A proper understanding of the epidemiology of drug resistance in tuberculosis in a country can only be achieved through well designed population-based surveys or routine surveillance among all TB patients.
As you know WHO updates country-level estimates of the burden of TB and drug-resistant TB every year as soon as new evidence becomes available. Unfortunately the results of this study are not helpful in this regard. In this region population-based national surveys are currently ongoing in Burkina Faso, Ghana, Ivory coast and a survey will soon start in Togo. These efforts are clearly not enough but will surly contribute to a better understanding of the magnitude of the problem of drug-resistant TB in these countries.