Asthma symptoms, severity, and control with and without a clinical diagnosis of asthma in early adolescence in sub-Saharan Africa: a multi-country, school-based, cross-sectional study.

Background: Rapid urbanisation and population growth in sub-Saharan Africa has increased the incidence of asthma in children and adolescents. One major barrier to achieving good asthma control in these adolescents is obtaining a clinical diagnosis. To date, there are scant data on prevalence and severity of asthma in undiagnosed yet symptomatic adolescents. We therefore aimed to assess symptom prevalence and severity, the effect of symptoms on daily life, and objective evidence of asthma in young adolescents from sub-Saharan Africa with and without a clinical diagnosis of asthma by spirometry and fractional exhaled nitric oxide (FeNO).

Methods: We designed a two-phase, multi-country, school-based, cross-sectional study to assess symptom prevalence and severity in sub-Saharan African adolescents. In phase 1 we surveyed young adolescents aged 12-14 years who were attending selected primary and secondary schools in Blantyre in Malawi, Durban in South Africa, Harare in Zimbabwe, Kampala in Uganda, Kumasi in Ghana, and Lagos in Nigeria. The adolescents were screened for asthma symptoms using the International Study of Asthma and Allergies in Children (ISAAC) questionnaire. Then, after opt-in consent, symptomatic adolescents were invited to complete a detailed survey on asthma severity, treatment, and exposure to environmental risk factors for phase 2. Adolescents performed the European Respiratory Society's diagnostic tests for childhood asthma. A positive asthma test was classified as a forced expiratory volume in 1 sec (FEV₁) predicted under 80%, a FEV₁ under the lower limits of normal, or FEV₁ divided by forced vital capacity (FEV₁/FVC) under the lower limits of normal; positive bronchodilator responsiveness or reversibility was defined as either an increase in absolute FEV₁ of 12% or more, or an increase of 200 mL or more, or both, after 400 μg of salbutamol (shortacting β2 agonist) administered via a metered-dose inhaler and spacer, or FeNO of 25 parts per billion or higher, or any combination of these. The study was registered with ClinicalTrials.gov (NCT03990402) and is complete.

Findings: Between Nov 1, 2018, and Nov 1, 2021, we recruited 149 schools from six regions in six sub-Saharan countries to participate in the study. We administered phase 1 asthma questionnaires from Jan 20, 2019 to Nov 11, 2021, and from 27 407 adolescents who were screened, we obtained data for 27 272 (99·5%). Overall, 14 918 (54·7%) adolescents were female and 12 354 (45·3%) adolescents were male, and the mean age was 13 years (IQR 12-13); nearly all recruited adolescents were of black African ethnicity (26 821 [98·3%] of 27 272). In phase 1, a total of 3236 (11·9% [95% CI 11·5-12·3]) reported wheeze in the past 12 months, and 644 (19·9%) of 3236 had a formal clinical diagnosis of asthma. The prevalence of adolescents with asthma symptoms ranged from 23·8% in Durban, South Africa to 4·2% Blantyre, Malawi. Using ISAAC criteria, severe asthma symptoms were reported by 2146 (66·3%) of 3236 adolescents, the majority of whom (1672 [77·9%] of 2146) had no diagnosis of asthma by a clinician. Between July 16, 2019, and Nov 26, 2021, we administered the phase 2 questionnaire to the 1654 adolescents who had asthma symptoms in phase 1 and consented to proceed to the second phase. In the phase 2 cohort, 959 (58·0%) were female and 695 (42·0%) were male, and the mean age was 13 years (IQR 12-14). One or more diagnostic tests for asthma were obtained in 1546 (93·5%) of 1654 participants. One or more positive asthma tests were found in 374 (48·8%) of 767 undiagnosed adolescents with severe symptoms, and 176 (42·4%) of 415 of undiagnosed adolescents with mild-to-moderate symptoms. Of the 392 adolescents in phase 2 with clinician-diagnosed asthma, 294 (75·0%) reported severe asthma symptoms, with 94 (32·0%) of those with severe symptoms not using any asthma medication. In general, findings in both phases 1 and 2 were consistent across sub-Saharan African countries.

Interpretation: A large proportion of adolescents in sub-Saharan Africa with symptoms of severe asthma do not have a formal diagnosis of asthma and are therefore not receiving appropriate asthma therapy. To improve the poor state of asthma control in sub-Saharan Africa, potential solutions such as educational programmes, better diagnosis, and treatment and screening in schools should be considered.

Funding: UK National Institute for Health and Care Research and UK Medical Research Council.