The prevalence and demographic associations of headache in the adult population of Benin: a cross-sectional population-based study

The protocol was approved by the Local Ethics Committee for Biomedical Research of the University of Parakou (CLERB-UP) under number 0168/CLERB-UP/P/SP/SA of April 10, 2019. The study was conducted in accordance with the Declaration of Helsinki [14].

Necessary authorizations from academic and administrative authorities were obtained. All participants were informed of the nature and purpose of the study and gave oral consent before enrolment. Anonymity and confidentiality of the information collected were respected in accordance with data-protection laws.

This was a cross-sectional study of the adult general population in Benin, using cluster-sampling to select a representative sample. In unannounced door-to-door visits to households, trained interviewers randomly selected, and interviewed, one member of each aged 18–65 years.

Pre-pilot and pilot studies tested the questionnaire and methods prior to the main study.

The pre-pilot study was carried out at the Centre Hospitalier Universitaire et Départemental over a period of 1 month using the first draft of the questionnaire to test its acceptability and comprehensibility. Respondents were 80 adults (aged 18–65 years), of whom 40 were patients presenting with headache and 40 were accompanying persons not complaining of headache. The study provided the basis for finalisation of the questionnaire.

Interviewers used the Headache-Attributed Restriction, Disability, Social Handicap and Impaired Participation (HARDSHIP) structured questionnaire developed by LTB [15], in the Central African French version used in Cameroon [7]. This questionnaire, described in detail previously, consists of several modules, three of which were used here: the demographic and social status module (enquiring into gender, age, habitation [urban or rural], marital status, education level and household income), and the headache diagnostic and description modules [15]. All participants completed the first module and answered the screening questions of the second (“have you ever had headache?” and “have you had headache during the last year?”). Only those responding positively to the latter question continued with the headache modules, describing their most bothersome headache if they had more than one type. Two questions asked whether headache had occurred on the day prior to the interview (“headache yesterday” [HY]) and whether, if so, it was of this type.

To obtain a representative sample of the general population of Benin, we recruited from three geographical regions (departments): Borgou (Parakou [urban] and Pèrèrè [rural]), Atlantique (Torri-Bossito [rural]) and Littoral (Cotonou [urban]) (Fig. 1).

The 12 interviewers were physicians or senior medical or epidemiology students. In a two-day session at Unité de Recherche Clinique et Epidémiologique (URCE), Faculty of Medicine, University of Parakou, they received instruction in headache disorders (basic epidemiological and clinical aspects) and the study (design, purpose and practical aspects). Competence was ensured in supervised interviews.

These interviewers conducted both the pilot and the main studies.

The pilot study field-tested the final version of the questionnaire in communities in Porto-Novo, a city 40 km from Cotonou, and in the surrounding rural areas. Using a mix of convenience and purposive sampling, 160 non-biologically related adults (aged 18–65 years) were interviewed, 40 urban and 120 rural.

Data from the pilot study were not included in the main analysis, but provided an estimate (with confidence interval [CI]) of the expected refusal rate.

This was completed between May 11th and July 4th, 2020.

Gender was recorded as a binary variable (male or female). Age was recorded as a continuous variable but later categorized: 18–25, 26–35, 36–45, 46–55 or 56–65 years. Habitation was recorded as urban or rural, marital status as single, married or widowed/separated/divorced, education level as none, primary school, secondary school or college+, and household income in West African francs (XOF) as < 10,000, 10,000–20,000, 20,001–50,000 or > 50,000. In June 2020, USD 1 = XOF 583.

Headache diagnoses were made algorithmically during analysis, according to responses to the HARDSHIP diagnostic module, which applied modified ICHD-3 criteria [16]. Only one diagnosis was allowed in each participant. The algorithm first identified those reporting headache on ≥ 15 days/month (H15+). Participants also reporting acute medication use on ≥ 15 days/month were categorized as having probable MOH (pMOH), on the assumption that only simple analgesics were available to the vast majority in a low-income country. The others were categorized as “other H15+”, with no further attempt at diagnosis. Participants reporting headache on < 15 days/month were categorized, as stipulated by ICHD-based criteria [16], in hierarchical order: definite migraine, definite TTH, probable migraine and probable TTH. Any remaining cases were unclassified.

Mean age, gender and habitation distributions in the sample were compared, using chi-squared tests, with those of Benin’s population aged 18–65 years.

We estimated 1-year prevalences as proportions (%) with 95% confidence intervals (CIs), reporting observed and age-, gender- and habitation-adjusted values for each headache type. We combined definite and probable migraine and definite and probable TTH in these and all further analyses. We estimated point prevalence of headache, as a proportion (%), from reported HY, and calculated the predicted point prevalence from the observed 1-year prevalence and mean headache frequency in days/month.

We used bivariate and multivariate analyses (calculating odds ratios [ORs] and adjusted ORs [aORs] with 95% CIs) to identify associations, if any, between each headache type and the demographic and social status variables. Significance was set at p < 0.05.

We used Microsoft Excel version 16 to calculate adjusted prevalences, and IBM-Statistical Package for Social Sciences statistical software (SPSS) version 28 (SPSS Inc., Chicago, IL) for all other analyses.

From 2,550 households with eligible members, we recruited 2,400 participants (participating proportion 94.1%). Of these, 50% were from Borgou, 35% from Atlantique and 15% from Littoral. The gender distribution in the sample (51.3% male) reflected that of Benin (49.8% male; chi-squared = 2.0; p = 0.15). Mean age in the sample was 32.1 years, similar in both genders, and slightly younger than the mean age of Benin’s inhabitants aged 18–65 years (34.6 years). Rural habitants were overrepresented (70% in the sample; 52% in the country as a whole; chi-squared = 311.5; p < 0.001).

Reported lifetime prevalence (headache ever) was 95.2%. Observed 1-year prevalence (headache reported in the last year) was 74.9%, slightly higher in females (77.6%) than males (72.3%). Table 1 summarizes the observed 1-year prevalences of all headache and each headache type by gender. Only 0.7% of headaches were unclassified.

TTH was by far the most prevalent headache (43.6%), almost twice as common as migraine (23.5%). H15 + was reported by 7.0%, categorized as pMOH in 4.2% and as other H15 + in 2.8 (Table 1). Age-, gender- and habitation-adjusted estimates differed somewhat from observed (any headache 72.9% [95% CI: 71.1–74.6]; migraine 21.2% [19.7–23.0]; TTH 43.1% [41.1–45.1]; pMOH 4.5% [3.7–5.4]; other H15 + 3.1% [2.4–3.9]).

Almost one in five (19.4%) of those with headache in the last year reported HY, equating to 14.8% [95% CI: 13.4–16.3] of the total sample, this being the point prevalence. The predicted point prevalence, from 1-year prevalence of any headache (74.9%) and mean headache frequency (4.3 days/month), was 10.7%. As expected, high proportions of those with pMOH (58.4%) and other H15+ (38.2%) reported HY. For migraine and TTH, the proportions were 18.1% and 11.0% respectively.

Bivariate and multivariate association analyses are shown in Tables 2 and 3. Numbers for other H15 + were small in many of these analyses.

With regard to gender, the higher prevalence of migraine among females (Table 1) was not significant in either analysis. TTH was not associated with gender (aOR = 1.0). pMOH was strongly associated with female gender (aOR = 2.5; p < 0.001), but there was no similar association for other H15+.

Prevalence of migraine was highest among those aged 18–35 years (Table 2), but variations were small and not significant. pMOH became increasingly prevalent with advancing age (Table 2). Other H15 + showed no association with age.

Migraine was associated with rural dwelling, TTH with urban dwelling. pMOH was least prevalent among those who were single, and most prevalent among those who were widowed, separated or divorced (Table 2), but these lost significance in multivariate analysis (Table 3). Migraine was negatively associated with educational level (Table 2), although this appeared only as a non-significant trend in multivariate analysis (Table 3). TTH was positively associated with educational level in both analyses. Migraine was most prevalent among those with least income (Table 2), but again this lost significance in multivariate analysis (Table 3). Other H15 + showed a strong negative association with household income (aOR = 6.1 for those in the lowest category) (Table 3).

Strengths were the use of standardized, expert-consensus-based and well tested methods [13] and questionnaire [15], an adequate sample (N = 2,400) drawn from multiple regions of the country in order to be representative of its diverse population, and a low non-participating proportion (5.9%). While we oversampled in rural areas (where migraine was more prevalent), statistical correction of prevalence estimates took full account of this.

The standardized methodology is designed to reduce the inherent limitations of questionnaire-based surveys. However, we were not able to test the validity of the diagnostic questions in the Central African French translation, since the resources for the necessary study (re-diagnosis of a subsample by a headache specialist) were not available in Benin. We relied on previous use of the same translation in Cameroon [7], and of the questionnaire in earlier Global Campaign studies in 19 languages [23], with validation studies in six [24–29]. In a cross-sectional survey with single enquiry, it is not realistically possible to diagnose more than one headache type. The focus on the most bothersome type was necessary to maintain clarity of description. In participants with both migraine and TTH, it would have been the latter that was not identified, meaning TTH prevalence was underestimated. MOH could be diagnosed only on the basis of association of H15 + and reported medication overuse, without evidence of causation (hence probable). The questionnaire, for reasons stated earlier, could not further diagnose other H15+, which might include secondary headaches, but among the other diagnostic possibilities were chronic migraine and chronic TTH. These would have been lost from our prevalence estimates, but the overall prevalence of other H15 + was only 3.1%. The proportion of unclassified cases was very low (0.7%).