Sources of Informations on D-R
Results from the national TB prevalence surveys: Unbiased and most reliable
Results from the nation-wide survey on D-R: Useful, in particular, if sampling is correct and re-testing is done by the reference laboratories.
Routine statistics on primary D-R: Easier to obtain in small countries and useful.
Informations from clinical laboratories: Often biased, as tests are often requested to treatment failure cases.
Problems in the Survey of Drug Resistance
Previous history of TB treatment
Difficulty in dividing cases into previously treated of untreated.
Primary D-R: among cases definitely previously untreated.
Initial D-R: among cases likely to be untreated previously
Difficulty in identifying Mycobacteria
Mixture of Mycobacteria other than M. tuberculosis is often seen.
Diversity in methods to measure D-R
International standardization is now going on.
Reliability on sources of informations on D-R
Review of the World-wide Situation of DR during the Period between 1985 and 1994.
Chon DL, Bustreo F, Raviglione MC (GTB, WHO)
