1.4 National TB prevalence surveys

To reliably track the burden of tuberculosis (TB) disease in terms of TB incidence and TB mortality from subnational to global levels, the ultimate goal is that all countries can rely on data routinely collected through a) national disease surveillance systems and b) vital registration (VR) systems in which causes of death are coded according to the international classification of diseases (ICD).

Currently, all countries have national systems for notification (i.e. reporting) of people diagnosed with TB and almost all countries report TB case notification data to the World Health Organization (WHO) on an annual basis (Section 2.1). However, in many countries (including most high TB burden countries) the number of notified cases each year is not a good proxy for the actual number of people who develop TB disease, for two reasons. The first is underreporting of people diagnosed with TB, especially in countries with large private sectors or in which people with TB seek care in public facilities that are not linked to the national TB programme and its associated reporting systems. The second is underdiagnosis, especially in countries with geographic or financial barriers to seeking health care. Many countries (including most high TB burden countries) do not have established national VR systems of high quality and coverage that can be used to reliably monitor the number of deaths and their cause (1).

In countries with a relatively high burden of TB disease that do not yet have national disease notification systems or national VR systems with cause-of-death data that are of sufficiently high quality and coverage, national TB prevalence surveys are the best way to directly measure the burden of TB disease in the population (2–4). In terms of disease burden, WHO currently recommends consideration of surveys according to previously documented epidemiological criteria (3, 4).

National TB prevalence surveys can provide a reliable measurement of the number of people in the population with bacteriologically confirmed pulmonary TB at a given point in time, and the distribution of these cases by age and sex. In addition, repeat surveys allow assessment of trends, and of the impact of interventions to reduce the burden of disease in the period since the last survey. WHO recommends that surveys focus on people aged 15 years or over (2).

Results can be used to inform national estimates of TB incidence in all age groups, and can thus help to track progress towards the milestones and targets for reductions in TB incidence set in the End TB Strategy (Section 1.1). Previously, survey results were also important for the assessment of progress towards global, regional and national targets for reductions in TB prevalence between 1990 and 2015.

For these reasons, the implementation of national TB prevalence surveys in 22 priority countries (referred to as global focus countries, GFCs) was one of three strategic areas of work defined by the WHO Global Task Force on TB Impact Measurement (the Task Force) for the period 2007–2015 (2, 3). National TB prevalence surveys were retained within the Task Force’s updated strategic areas of work after 2015 (4, 5).

Other benefits of prevalence surveys include that they can be used to document health care seeking behaviour in the public and private sectors, assess variation in underreporting or underdiagnosis of TB by age and sex (using the ratio of prevalence to notifications), and quantify the extent of underreporting of people diagnosed with TB to national authorities. Findings can help to inform the development or improvement of TB case finding, diagnosis and treatment interventions.

Between 2000 and August 2023, a total of 43 national TB prevalence surveys in 34 countries were implemented; of these, 40 used the screening and diagnostic methods recommended by WHO (Fig. 1.4.1). These 34 countries comprised 18 in Africa and 16 in Asia, and 20 of the 22 GFCs. Five countries implemented repeat surveys: China, Cambodia, Myanmar, the Philippines and Viet Nam. Timor-Leste started its first survey in December 2022, and Cambodia started its third survey in July 2023 (Fig. 1.4.2).

A growing number of countries are actively interested in implementing a repeat prevalence survey in the next 1–3 years: Ethiopia, Ghana, Malawi, Nigeria, Uganda, the United Republic of Tanzania, Zambia and Zimbabwe in Africa; and Indonesia, Pakistan and Thailand in Asia.

Fig. 1.4.3 Estimates of the prevalence of bacteriologically confirmed pulmonary TB in surveys completed 2007-2021^a

In African countries, prevalence ranged from 119 (95% confidence interval [CI]: 79–160) per 100 000 population in Rwanda (in 2012) to 852 (95% CI: 679–1026) per 100 000 population in South Africa (in 2017). In Asian countries, prevalence ranged from 119 (95% CI: 103–135) per 100 000 population in China (in 2010) to 1159 (95% CI: 1016–1301) per 100 000 population in the Philippines (in 2016).

In most Asian countries and some African countries, prevalence increased with age (Fig. 1.4.4, Fig. 1.4.5).

Fig. 1.4.4 Estimated age-specific prevalence of bacteriologically confirmed pulmonary TB for surveys implemented in Africa, 2010–2019^a

Fig. 1.4.5 Estimated age-specific prevalence of bacteriologically confirmed pulmonary TB for surveys implemented in Asia, 2007–2021