2.3 Drug-resistant TB
Since 1994, the World Health Organization (WHO) has systematically collected and analysed data on levels of resistance to anti-TB drugs from countries and territories (1). Until 2020, these data were used to produce estimates of the number of incident cases of rifampicin-resistant or multidrug-resistant TB (defined as resistance to both rifampicin and isoniazid), collectively referred to as MDR/RR-TB, and the proportions of TB cases with various combinations of resistance to first-line and second-line drugs, for the latest complete calendar year. This was done at global, regional and country levels. An important limitation of this approach was that only the most recent data point from each country was used, with no analysis of trends. In 2022, new methods were developed to produce time series of estimates for the period 2015–2021 (2, 3).
Globally, there were an estimated 450 000 incident cases (95% uncertainty interval [UI]: 399 000–501 000) of MDR/RR-TB in 2021, up 3.1% from 437 000 (95% UI: 390 000–483 000) in 2020 (Fig. 2.3.1).
The main explanation for this increase is an overall increase in TB incidence between 2020 and 2021, which is estimated to have occurred as a result of the impact of the COVID-19 pandemic on TB detection (Section 2.1). An estimated 191 000 (range 119 000–264 000) deaths occurred due to MDR/RR-TB in 2021.
Fig. 2.3.1 Global trend in the estimated number of incident cases of MDR/RR-TB, 2015–2021
The shaded area represents the 95% uncertainty interval.
Globally, the estimated proportion of new TB cases with MDR/RR-TB was 3.9% (95% UI: 2.8–5.0%) in 2015 and 3.6% (95% UI: 2.7–4.4%) in 2021; the proportion of previously treated cases was 20% (95% UI: 9.5–31%) in 2015 and
18% (95% UI: 11–26%) in 2021 (Fig. 2.3.2).
Fig. 2.3.2 Global percentage of TB cases with MDR/RR-TB, 2015–2021
The shaded area represents the 95% uncertainty interval.
Trends at regional level vary (Fig. 2.3.3). Four regions have patterns similar to the global trend, with an increase between 2020 and 2021. The two exceptions are the
Eastern Mediterranean Region and the Region of the Americas, where there have been slow increases over a period of several years.
Fig. 2.3.3 Regional trends in the estimated number of incident cases of MDR/RR-TB, 2015–2021
The shaded area represents the 95% uncertainty interval.
Trends in the 30 high MDR/RR-TB burden countries also vary (Fig. 2.3.4).
Fig. 2.3.4 Country-specific trends in the estimated number of incident cases of MDR/RR-TB, a 2015–2021
The shaded area represents the 95% uncertainty interval.
The countries with the largest share of incident cases of MDR/RR-TB in 2021 were India (26% of global cases), the Russian Federation (8.5% of global cases) and Pakistan (7.9% of global cases) (Fig. 2.3.5).
Fig. 2.3.5 Estimated number of incident cases of MDR/RR-TB in 2021, for countries with at least 1000 incident cases
The seven countries with the highest burden in terms of numbers of MDR/RR-TB cases, and that accounted for two thirds of global MDR/RR-TB cases in 2021, are labelled.
The proportion of TB cases with MDR/RR-TB varies considerably among regions and countries (Fig. 2.3.6, Fig. 2.3.7).
For new cases, best estimates range from less than 4% in the WHO African, South-East Asian and Western Pacific regions and Region of the Americas, to 26% in the European Region. For previously treated cases, they range from 7.9% in the Eastern
Mediterranean Region to 57% in the European Region. At country level, the highest proportions are found in the Russian Federation and in several countries in eastern Europe and Central Asia.
Fig. 2.3.7 Percentage of previously treated TB cases with MDR/RR-TB, 2021
Globally in 2021, the estimated proportion of MDR/RR-TB cases with pre-XDR (i.e. resistance to any fluoroquinolone for which testing was done) was 20% (95% CI: 16-26%).
Sources of data on levels of drug resistance include routine surveillance and survey data. For 182 countries and territories worldwide, at least one representative data point for rifampicin is available from the past 15 years, collectively accounting for more than 94% of the world’s population and incident cases of TB.
With the expansion of rapid molecular tools, an increasing number of countries have transitioned from a reliance on periodic surveys to the establishment of continuous surveillance systems based on routine drug susceptibility testing (DST) of Mycobacterium tuberculosis isolates for at least rifampicin, and for at least 80% of patients with bacteriologically confirmed pulmonary TB (4). Of the 182 countries and territories with representative data, 151 have continuous surveillance systems and 31 rely on epidemiological surveys of bacterial isolates collected from representative samples of patients (Fig. 2.3.8, Fig. 2.3.9, Fig. 2.3.10). A total of 38 of the 43 countries that are in one or both of the WHO lists of high TB burden and high MDR/RR-TB burden countries being used in the period 2021–2025 have data on levels of drug resistance.
Fig. 2.3.9 Most recent year of data on rifampicin resistance among new cases, 1996–2022 a
a Ongoing in 2022 refers to first-ever national surveys of anti-TB drug resistance that are being planned or implemented. For countries that are planning or implementing repeat surveys, the most recent year of data is shown.
Fig. 2.3.10 Number of data points on rifampicin resistance among new cases, 1996–2022 a
a In 2022, a first-ever national drug-resistance survey was completed in Niger, and a repeat survey was completed in Mozambique.
References
Dean AS et al (2022). 25 years of surveillance of drug-resistant tuberculosis: achievements, challenges, and way forward. Lancet Infect Dis 22(7):E191-E196 (https://doi.org/10.1016/S1473-3099(21)00808-2)
WHO Global Task Force on TB Impact Measurement: report of a subgroup meeting on methods used by WHO to estimate TB disease burden, 11-12 May 2022, Geneva, Switzerland. Geneva: WHO; 2022 (https://apps.who.int/iris/bitstream/handle/10665/363428/9789240057647-eng.pdf)
Background document 2. Methods for estimating the incidence of drug-resistant TB. In: WHO/Global Task Force on TB Impact measurement [website]. Geneva: WHO; 2022 (https://cdn.who.int/media/docs/default-source/hq-tuberculosis/global-task-force-on-tb-impact-measurement/meetings/2022-05/tf-2022-05-2-background--document-2--dr-tb.pdf?sfvrsn=a8757cfa_3)
Guidance for the surveillance of drug resistance in tuberculosis: Sixth edition. Geneva: WHO; 2021 (https://www.who.int/publications/i/item/9789240018020).