17.3 Case detection and enrolment

17.3.1 Case detection and enrolment data

For case detection, patients counted are those diagnosed with TB, whether started on TB treatment or not.

For enrolment, patients counted are those started on TB treatment.

 

In principle, the number of patients detected and enrolled during the same period is identical. Any difference requires explanation.

 

Detection and enrolment data are collected after the end of the reporting period. For example, for patients diagnosed and started on TB treatment during the first semester 2024 (January to June 2024), data are reported in July 2024.

 

For an example of case detection and enrolment report, see Appendix 37.

17.3.2 Definitions of TB cases

Patients with active TB are classified according to the following criteria [1] Citation 1. World Health Organization. Definitions and reporting framework for tuberculosis – 2013 revision (updated December 2014 and January 2020). Geneva: World Health Organization; 2020.
https://apps.who.int/iris/bitstream/handle/10665/79199/9789241505345_eng.pdf :

• Bacteriological status: confirmed TB, not confirmed TB
• Drug susceptibility pattern: drug-susceptible TB, drug-resistant TB
• Anatomical site of the disease: pulmonary TB (PTB), extrapulmonary TB (EPTB)
• History of previous TB treatment: new patient, previously treated patient (including relapse/recurrence, treatment failure, lost to follow-up, other previously treated patients)
• HIV status: positive, negative, unknown.

 

For more information, see Chapter 7.

17.3.3 Case detection and enrolment indicators

The following indicators are the basic indicators to be calculated. Depending on the context, other indicators may be added (e.g. proportion of treatment failures, proportion of pre-XDR-TB cases, proportion of children, proportion of adolescents). These indicators are calculated for a given reporting period (every 3, 6 or 12 months).

 

Numerators and denominators are taken from the TB registers, except for:

• Proportion of patients with susceptibility or resistance among patients with DST result: the denominator is taken from the laboratory register.
• Detection rates: the denominator is calculated from the TB incidence rate reported by the national TB programme (at national or regional level) or, if not available, from the TB incidence rate reported in the WHO country profile a Citation a. For WHO country profiles:
  https://worldhealthorg.shinyapps.io/tb_profiles/?_inputs_&entity_type=%22group%22&lan=%22FR%22 . For example:
  • Patients with TB: in a country with a TB incidence rate of 348 cases/100,000 inhabitants/year, the expected number of TB cases in a district of 30,000 inhabitants is: 348 x 30,000 ÷ 100,000 = 104 per year,
  • Patients with MDR/RR-TB: in a country with an MDR/RR-TB incidence rate of 15 cases/100,000 inhabitants/year, the expected number of MDR/RR-TB cases in a district of 30,000 inhabitants is: 15 x 30,000 ÷ 100,000 = 4 to 5 per year.
• Proportion of patients started on latent TB infection (LTBI) treatment: data are taken from a specific LTBI register. 

 

Table 17.1 − Case detection indicators

 

 

The proportion of patients with bacteriologically confirmed PTB is expected to be > 65% [2] Citation 2. World Health Organization. Global Tuberculosis Report 2023. Geneva: World Health Organization; 2023.
https://www.who.int/teams/global-tuberculosis-programme/tb-reports . However, for children and patients with HIV infection, this proportion is lower due to the poor sensitivity of RMTs on paucibacillary specimens.

 

The proportion of patients with bacteriologically confirmed PTB detected by an RMT should be close to 100% as RMT is the recommended initial diagnostic test. A proportion that differs significantly requires explanation.

 

The proportion of patients with EPTB usually ranges between 8 and 24% [3] Citation 3. World Health Organization. Global Tuberculosis Report 2020. Geneva: World Health Organization; 2020.
https://www.who.int/publications/i/item/9789240013131 , but can vary considerably depending on the local epidemiology (e.g. in a retrospective study in Ethiopia, EPTB represented nearly 50% of TB cases [4] Citation 4. Arega B, Mersha A, Minda A, Getachew Y, Sitotaw A, Gebeyehu T, et al. (2020) Epidemiology and the diagnostic challenge of extra-pulmonary tuberculosis in a teaching hospital in Ethiopia. PLoS ONE 15(12): e0243945.
https://doi.org/10.1371/journal.pone.0243945 ). A proportion that differs significantly from national data for EPTB requires explanation.

 

A high proportion (> 20%) of patients previously treated requires explanation. It can indicate one or several problem(s) [5] Citation 5. European Centre for Disease Prevention and Control. Tuberculosis in Europe: From passive control to active elimination. Stockholm: ECDC; 2015.
https://www.ecdc.europa.eu/sites/default/files/media/en/publications/Publications/tuberculosis-evidence-brief-low-high-incidence-countries.pdf :

• poorly organised services and lack of patient support (high proportion of "lost to follow-up")
• high level of undiagnosed resistance (high proportion of "treatment failures")
• significant ongoing transmission, resulting in re-infections (high proportion of "recurrences").

 

The proportion of children and young adolescents among TB cases depends on the proportion of children and young adolescents in the population. In general, approximately 12% [2] Citation 2. World Health Organization. Global Tuberculosis Report 2023. Geneva: World Health Organization; 2023.
https://www.who.int/teams/global-tuberculosis-programme/tb-reports of total TB cases are expected to be < 15 years. A proportion that differs significantly requires explanation.

 

The detection rates reflect performance of diagnostic activities. If the denominator for this indicator is calculated from the incidence rate for the entire country, it does not reflect possible variations between different regions of the country. Therefore, a detection rate < 100% does not necessarily reflect poor performance of diagnostic activities. It can be explained by a regional incidence rate below the national incidence rate. However, a low detection rate requires explanation.

 

Table 17.2 − HIV detection indicators

 

The proportion of patients with known HIV status should be 100%. A lower proportion requires explanation.

In high HIV-prevalence areas, co-infection rate may exceed 70% [6] Citation 6. Kerschberger B, et al. Decreased risk of HIV-associated TB during antiretroviral therapy expansion in rural Eswatini from 2009 to 2016: a cohort and population-based analysis. Trop Med Int Health. 2019 Sep;24(9):1114-1127.
https://doi.org/10.1111/tmi.13290 .
 

Table 17.3 − Enrolment indicators

 

The proportion of patients started on treatment is expected to be 100% for patients with active TB (all resistance profiles) and 100% for patients eligible for LTBI treatment. Proportions that differ significantly require explanation.