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. 2020 Nov;25(11):1308-1327.
doi: 10.1111/tmi.13485. Epub 2020 Oct 12.

National tuberculosis prevalence surveys in Africa, 2008-2016: an overview of results and lessons learned

Irwin Law  1 , Katherine Floyd  1 ; African TB Prevalence Survey Group
Collaborators, Affiliations

National tuberculosis prevalence surveys in Africa, 2008-2016: an overview of results and lessons learned

Irwin Law et al. Trop Med Int Health. 2020 Nov.

Abstract
in English, French

Objective and methods: Worldwide, tuberculosis (TB) is the leading cause of death from a single infectious agent. In many countries, national TB prevalence surveys are the only way to reliably measure the burden of TB disease and can also provide other evidence to inform national efforts to improve TB detection and treatment. Our objective was to synthesise the results and lessons learned from national surveys completed in Africa between 2008 and 2016, to complement a previous review for Asia.

Results: Twelve surveys completed in Africa were identified: Ethiopia (2010-2011), Gambia (2011-2013), Ghana (2013), Kenya (2015-2016), Malawi (2013-2014), Nigeria (2012), Rwanda (2012), Sudan (2013-2014), Tanzania (2011-2012), Uganda (2014-2015), Zambia (2013-2014) and Zimbabwe (2014). The eligible population in all surveys was people aged ≥15 years who met residency criteria. In total 588 105 individuals participated, equivalent to 82% (range 57-96%) of those eligible. The prevalence of bacteriologically confirmed pulmonary TB disease in those ≥15 years varied from 119 (95% CI 79-160) per 100 000 population in Rwanda and 638 (95% CI 502-774) per 100 000 population in Zambia. The male:female ratio was 2.0 overall, ranging from 1.2 (Ethiopia) to 4.1 (Uganda). Prevalence per 100 000 population generally increased with age, but the absolute number of cases was usually highest among those aged 35-44 years. Of identified TB cases, 44% (95% CI 40-49) did not report TB symptoms during screening and were only identified as eligible for diagnostic testing due to an abnormal chest X-ray. The overall ratio of prevalence to case notifications was 2.5 (95% CI 1.8-3.2) and was consistently higher for men than women. Many participants who did report TB symptoms had not sought care; those that had were more likely to seek care in a public health facility. HIV prevalence was systematically lower among prevalent cases than officially notified TB patients with an overall ratio of 0.5 (95% CI 0.3-0.7). The two main study limitations were that none of the surveys included people <15 years, and 5 of 12 surveys did not have data on HIV status.

Conclusions: National TB prevalence surveys implemented in Africa between 2010 and 2016 have contributed substantial new evidence about the burden of TB disease, its distribution by age and sex, and gaps in TB detection and treatment. Policies and practices to improve access to health services and reduce under-reporting of detected TB cases are needed, especially among men. All surveys provide a valuable baseline for future assessment of trends in TB disease burden.

OBJECTIF ET MÉTHODES: Dans le monde entier, la tuberculose (TB) est la principale cause de décès par un seul agent infectieux. Dans de nombreux pays, les surveillances nationales de prévalence de la TB sont le seul moyen de mesurer de manière fiable la charge de la TB et peuvent également fournir d'autres données pour éclairer les efforts nationaux visant à améliorer la détection et le traitement de la TB. Notre objectif était de synthétiser les résultats et les leçons tirées des surveillances nationales réalisées en Afrique entre 2008 et 2016, pour complémenter une analyse précédente pour l'Asie. RÉSULTATS: Douze surveillances réalisées en Afrique ont été identifiés: Ethiopie (2010-2011), Gambie (2011-2013), Ghana (2013), Kenya (2015-2016), Malawi (2013-2014), Nigeria (2012), Rwanda (2012), Soudan (2013-2014 ), Tanzanie (2011-2012), Ouganda (2014-2015), Zambie (2013-2014) et Zimbabwe (2014). La population éligible dans toutes les surveillances était des personnes ≥15 ans qui répondaient aux critères de résidence. Au total, 588.105 personnes ont participé, ce qui équivaut à 82% (entre 57% et 96% ) des personnes éligibles. La prévalence de la TB pulmonaire bactériologiquement confirmée chez les ≥15 ans variait de 119 (IC95%: 79-160) pour 100.000 habitants au Rwanda et 638 (IC95%: 502 à 774) pour 100.000 habitants en Zambie. Le ratio hommes/femmes était globalement de 2,0, allant de 1,2 (Ethiopie) à 4,1 (Ouganda). La prévalence pour 100.000 habitants augmentait généralement avec l'âge, mais le nombre absolu de cas était généralement le plus élevé chez les 35 à 44 ans. Parmi les cas de TB identifiés, 44% (IC95%: 40-49) n'ont pas rapporté de symptômes de TB lors du dépistage et n'ont été identifiés comme éligibles aux tests de diagnostic qu'en raison d'une radiographie pulmonaire anormale. Le rapport global entre la prévalence et les notifications de cas était de 2,5 (IC95%: 1,8-3,2) et était systématiquement plus élevé pour les hommes que pour les femmes. De nombreux participants qui avaient rapporté des symptômes de TB n'avaient pas recherché des soins; ceux qui en avaient étaient plus susceptibles de rechercher des soins dans un établissement de santé publique. La prévalence du VIH était systématiquement plus faible parmi les cas prévalents que chez les patients TB officiellement notifiés avec un rapport global de 0,5 (IC95% 0,3 - 0,7). Les deux principales limitations de l'étude étaient les suivantes: aucune des surveillances n'incluait des personnes de moins de 15 ans et 5 des 12 surveillances ne contenaient pas de données sur le statut VIH. CONCLUSIONS: Les surveillances nationales sur la prévalence de la TB en Afrique menées entre 2010 et 2016 ont fourni de nouvelles données sur la charge de morbidité de la TB, la répartition par âge et par sexe, et les lacunes dans la détection et le traitement de la TB. Des politiques et des pratiques pour améliorer l'accès aux services de santé et réduire la sous-déclaration des cas de TB détectés sont nécessaires, en particulier chez les hommes. Toutes les surveillances fournissent une base précieuse pour l'évaluation future des tendances de la charge de morbidité TB.

Keywords: Africa; Tuberculosis; epidemiology; prevalence survey; public health.

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Figures

Figure 1
Figure 1
a The WHO Global Task Force on TB impact Measurement selected 22 global focus countries (GFC) to undertake a national TB prevalence survey during the period 2008- 2015. Of the 13 GFCs in Africa, nine completed a survey (violet) between 2010-2016. The other four GFCs that did not conduct a survey during 2010-2016 were Mali, Mozambique, Sierra Leone and South Africa (pink). DPR Korea, Gambia, Lao PDR, Mongolia, Sudan and Zimbabwe completed a survey during the period 2010-2016 but were not GFCs (skyblue). Grey, not applicable. Countries that completed a national TB prevalence survey, 2008–2016a.
Figure 2
Figure 2
Participation rate by sex and age group in national TB prevalence surveys implemented in Africa, 2008–2016. Female (red), Male (green).
Figure 3
Figure 3
a Countries are listed in decreasing order according to the before-after difference. The vertical line denotes the best estimate of prevalence and its range (depicted as a 95% uncertainty interval). These prevalence estimates were indirectly derived from estimates of incidence and the duration of disease previously published by WHO, adjusted to the year of the prevalence survey using previously published trends in incidence. Estimates of TB prevalence (all ages, all forms of TB) for 12 surveys, before (in blue) and after (in red) results from national TB prevalence surveys implemented in Africa, 2008–2016a.
Figure 4
Figure 4
a The size of the best estimate (black square) is proportional to the model’s weights (inverse variance). b The sex ratio of smear-positive TB prevalence is shown for Tanzania. The sex ratio (male to female) of bacteriologicallyconfirmed pulmonary TB cases detected in national TB prevalence surveys implemented in Africa, 2008–2016a.
Figure 5
Figure 5
a Bacteriologically-confirmed TB cases could not be verified, so the value for smear-positive TB is shown instead. Estimated age-specific prevalence of bacteriologically-confirmed pulmonary TB in national TB prevalence surveys implemented in Africa, 2008–2016. The pink line denotes the best estimate and the blue shaded areas are the 95% confidence intervals.
Figure 6
Figure 6
a The size of the best estimate (black square) is proportional to the model’s weights (inverse variance). b Bacteriologically-confirmed TB cases could not be verified for Tanzania, so the value for smear-positive TB is shown instead. Percentage of bacteriologically-confirmed pulmonary TB cases who screened symptom negative in national TB prevalence surveys completed in Africa, 2008–2016a.
Figure 7
Figure 7
a The comparison is for smear-positive pulmonary TB for all countries except Kenya, Uganda and Zimbabwe, for which the comparison is for bacteriologically confirmed pulmonary TB. The size of the best estimate (black square) is proportional to the model’s weights (inverse variance). Prevalence to notification (P:N) ratio for TB cases in national TB surveys implemented in Africa, 2008–2016a.
Figure 8
Figure 8
aThe proportions of TB survey cases with known HIV status and notified TB cases that were HIV-positive, respectively, were as follows: Kenya (0.17, 0.31), Malawi (0.28, 0.55), Rwanda (0.03, 0.26), Tanzania (0.08, 0.37), Uganda (0.27, 0.44), Zambia (0.27, 0.61) and Zimbabwe (0.51, 0.69). The size of the best estimate (black square) is proportional to the model’s weights (inverse variance). b Bacteriologically-confirmed TB cases could not be verified for Tanzania, so the value for smear-positive TB is shown instead. HIV prevalence in TB survey cases compared with notified TB cases, expressed as a ratio, in national TB prevalence surveys implemented in Africa, 2008–2016a.
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