Methods: Monitoring the detection and treatment of TB cases
Focusing on new smear-positive cases, treatment success is the proportion of patients who complete their entire course of treatment, with or without bacteriological confirmation of cure (Table 2).11 Cure and completion are among the 6 mutually exclusive outcomes in DOTS cohort analysis.12 These 6 possible outcomes, plus the fraction of cases not evaluated, add up to 100%.13
We also compare the number of new cases registered for treatment in 2001 with the number of cases notified as smear-positive (also in 2001). All registered cases should be evaluated, and the numbers registered and evaluated should therefore be the same (discrepancies arise e.g. when sub-national reports are not received at national level). If the number registered is not provided, we use the number notified for the cohort year as the denominator. (For retreatment outcomes, we cannot assess how many cases should have been registered on retreatment regimens.)
DOTS population coverage
We define coverage as the percentage of people living in areas where health services have adopted the DOTS strategy. The units of population covered are usually the administrative units used for other purposes within countries (e.g. counties, districts, oblasts), and the outcome is usually expressed as a percentage of the national population. DOTS coverage is used in this report to monitor progress during the geographic expansion of DOTS programmes, and is based on information available to the NTP.14
Population units nominally covered by DOTS do not necessarily provide full access to DOTS services. Access to health services varies widely, within and among countries, according to the number and distribution of health centres, travel time for patients, transportation infrastructure, the number and type of health care providers, out-of-pocket costs to patients, and other factors. There is no standard, international measure of "access", though there are working definitions in some countries (e.g. living within 10km of a health facility in Ethiopia). In general, the precise definition and assessment of DOTS population coverage is left to the NTP, and interpretations inevitably differ among countries.
In the context of measuring access to DOTS, the ratio of DDR to population coverage estimates the case detection rate within DOTS areas (as distinct from the case detection rate nationwide), assuming that the TB incidence rate is homogeneous across counties, districts, provinces, or other administrative units. Ideally, this ratio would have a value of 70% or more as DOTS coverage increases within any country. Where the value of this indicator is much lower, it suggests that the DOTS programme has been poorly implemented. Changes in the value of this ratio through time are a measure of changes in the quality of TB control, after the DOTS programme has been established.
11 TB control programmes should ensure high treatment success before expanding case detection. The reason is that a proportion of patients given less than a fully-curative course of treatment remain chronically infectious, and continue to spread TB. Thus DOTS programmes must be shown to achieve high cure rates in pilot projects before attempting countrywide coverage.
12 Veen J, Raviglione MC, Rieder HL, Migilori GB, Graf P, Grzemska M, Zalesky R. Standardized tuberculosis treatment outcome monitoring in Europe. European Respiratory Journal 1998; 12: 505 510.
13 Although treatment outcomes are expressed as percentages, they are usually referred to as 'rates' (as for case detection).
14 The term "coverage" is used by health programmes in various ways, and has sometimes been misinterpreted in the context of DOTS. For example, coverage is neither the number of patients treated, nor the number of patients receiving DOT, but rather the fraction of the population living in areas where health services have adopted the DOTS strategy (usually expressed as %).