Non-communicable diseases in sub-Saharan Africa: a scoping review of large cohort studies

Abstract

Background: Non-communicable diseases (NCDs) cause a large and growing burden of morbidity and mortality in sub-Saharan Africa. Prospective cohort studies are key to study multiple risk factors and chronic diseases and are crucial to our understanding of the burden, aetiology and prognosis of NCDs in SSA. We aimed to identify the level of research output on NCDs and their risk factors collected by cohorts in SSA.

Methods: We conducted a scoping review to map the extent of current NCDs research in SSA by identifying studies published after the year 2000 using prospectively collected cohort data on any of the six NCDs (cardiovascular diseases, diabetes, obesity, chronic kidney disease, chronic respiratory diseases, and cancers), ≥1 major risk factor (other than age and sex), set only within SSA, enrolled ≥500 participants, and ≥12 months of follow-up with ≥2 data collection points (or with plans to). We performed a systematic search of databases, a manual search of references lists from included articles and the INDEPTH network website, and study investigators from SSA were contacted for further articles.

Results: We identified 30 cohort studies from the 101 included articles. Eighteen countries distributed in West, Central, East and Southern Africa, were represented. The majority (27%) set in South Africa. There were three studies including children, twenty with adults, and seven with both. 53% of cohorts were sampled in general populations, 47% in clinical populations, and 1 occupational cohort study. Hypertension (n = 23) was most commonly reported, followed by obesity (n = 16), diabetes (n = 15), CKD (n = 6), COPD (n = 2), cervical cancer (n = 3), and breast cancer (n = 1). The majority (n = 22) reported data on at least one demographic/environmental, lifestyle, or physiological risk factor but these data varied greatly.

Conclusions: Most studies collected data on a combination of hypertension, diabetes, and obesity and few studies collected data on respiratory diseases and cancer. Although most collected data on different risk factors the methodologies varied greatly. Several methodological limitations were found including low recruitment rate, low retention rate, and lack of validated and standardized data collection. Our results could guide potential collaborations and maximize impact to improve our global understanding of NCDs (and their risk factors) in SSA and also to inform future research, as well as policies.

Figure 1

Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) flow diagram for study selection process.

Figure 2

Map of non-communicable disease (NCD) cohorts found in SSA countries.

Figure 3

Risk factor data reported in each study categorised into demographic and environmental (D&E), lifestyle (L), and physiological (P) risk factors. A white (or empty) circle represents the absence of basic (outside circle), core (middle), or expanded (inside) level of risk factor data, and a coloured circle represents the presence of basic (orange), core (yellow), or expanded (green) level of risk factor data. D&E – Demographic & environmental risk factor data; L – Lifestyle risk factor data; P – Physiological risk factor data; CKD – chronic kidney disease; COPD – chronic obstructive pulmonary disease; CC – cervical cancer; BC – breast cancer; ACCME – African Collaborative Centre for Microbiome and Genomics Research; HAALSI – Health & Aging in Africa – Longitudinal Studies of INDEPTH Communities; NCD – non-communicable diseases; DUCS-HTN – the Dar es Salaam Urban Cohort Hypertension study; ABC-DO – African Breast Cancer – Disparities in Outcomes study; HARP – HPV in Africa Research Partnership; CoLTART – the Complications of Long-Term Antiretroviral Therapy study; RWISA – Rwanda Women’s Interassociation Study and Assessment; UARTO – Uganda AIDS Rural Treatment Outcomes study.