Prevalence of Hidradenitis Suppurativa in Berekum, Ghana

Dear Editor, Hidradenitis Suppurativa (HS) is a scarring and painful skin disease that affects the intertriginous regions of the skin.1 A wide variation in prevalence data has been described, depending on the studied population and the sampling method.1 A systematic review and meta‐analysis reported an overall HS prevalence of 0·40% [95% confidence interval (CI) 0·26–0·63].1 The wide variation in prevalence of HS may be an expression of different genetic or environmental factors. The diagnostic criteria for HS are typical lesions, typical topography and chronicity.2 These clear clinical criteria allow the diagnosis to be made using a simple questionnaire, such as that created by Vinding et al. which has undergone preliminary validation in an exploratory study in Ghana.2,3 The prevalence rate found in this exploratory study suggested the need for a larger sample size. We conducted sample size calculations based on our previous data according to the approach by Humphry et al.4 To further bolster the analysis, the assumed sensitivity and specificity of the sample size calculation were set to 0·15 lower than those obtained in the exploratory study.2 Consequently, a required sample of 1440 participants was deemed sufficient to calculate the true prevalence and avoid underpowering of the analysis. We therefore conducted a validation study to confirm the previous data.2 Healthy adults accompanying patients attending the General Outpatient Department of the Holy Family Hospital were included. After obtaining oral and written informed consent, participants were invited to answer a questionnaire previously translated into Twi (Akan language).2 The questionnaire also contained basic demographic questions (Table 1). Participants who screened positive and 10% of participants who screened negative were clinically assessed by a dermatologist to verify the findings. This helped to reduce bias. Descriptive statistics and test parameters BMI, body mass index; HS, Hidradenitis Suppurativa; IQR, interquartile range; NA, not available. Sensitivity 1 (10 of 10), specificity 0·89 (140 of 156), positive predictive value 0·38 (10 of 26) and negative predictive value 1 (140 of 140). aThe boil questionnaire consisted of two questions created by Vinding et al.3 (i) ‘Have you had outbreaks of boils during the last 6 months?’ (ii) ‘Have you for the past 6 months had two or more boils/abscesses in any of the below locations?’ with five different location options [axilla, groin, genitals, under the breasts and other locations (not specified), e.g. perianal region, neck and abdomen]. Descriptive statistics and test parameters BMI, body mass index; HS, Hidradenitis Suppurativa; IQR, interquartile range; NA, not available. Sensitivity 1 (10 of 10), specificity 0·89 (140 of 156), positive predictive value 0·38 (10 of 26) and negative predictive value 1 (140 of 140). aThe boil questionnaire consisted of two questions created by Vinding et al.3 (i) ‘Have you had outbreaks of boils during the last 6 months?’ (ii) ‘Have you for the past 6 months had two or more boils/abscesses in any of the below locations?’ with five different location options [axilla, groin, genitals, under the breasts and other locations (not specified), e.g. perianal region, neck and abdomen]. A total of 1517 participants were approached, but owing to missing data and/or consent, 31 individuals were excluded. The estimated true prevalence of HS in the remaining sample of 1486 participants was 0·67% (10 of 1486, 95% CI 0·37–1·23). A subset of 140 randomly selected screen‐negative participants were examined clinically, and none had HS. This finding indicated against the need for correcting any possible verification bias, although it remains an important limitation. There was no significant difference relating to age, sex, smoking status or body mass index (BMI) between the control group and the HS group (Table 1). The test specifics of the screening questionnaire were as follows: sensitivity 1·00, specificity 0·89, positive predictive value (PPV) 0·38 and negative predictive value 1 (Table 1). Most of the available prevalence data for HS originate from Europe, the USA and Australia. Data from other parts of the world are lacking, resulting in a global knowledge gap. The prevalence in our previous study in Ghana was 0·8%. In this larger follow‐up study, we found a prevalence of 0·67%, which is equal to the HS prevalence reported in Australia using the same validated questionnaire.5 Furthermore, it is not dissimilar to the prevalence reported from a registry study in the UK (point prevalence 0·77%).6 Additionally, this larger follow‐up study also reports a sensitivity of 1 and a specificity of 0·89, which is similar to our previous findings (sensitivity 1, specificity 0·74). PPV was low in our study. This was expected owing to the low reported prevalence of HS. This is not a limitation in itself, as this value is not transferable to other populations. In our exploratory study,2 75% of the HS cases occurred in women (three of four), and in the current study we found a similar distribution, with 80% of HS cases occurring in women (8 of 10). The UK registry study6 similarly reported a female to male ratio of 2·9 : 1 (74·4% female) across all ages, while 66·7% of the HS cases in the prevalence study from Australia occurred in women.5 However, a study by Chandran et al.7 investigated the HS prevalence in Southeast and East Asia, and the prevalence was reported as 0·06% with a male predominance. Furthermore, our cohort is unique, as it has a low rate of smokers and obese participants. (Table 1). Smoking and obesity have been recognized as environmental factors with a high impact on HS,8 and 50% (5 of 10) of participants with HS in our study were obese (BMI > 30), although there was no significant difference between the HS group and the control group in relation to BMI (P = 0·1). None of the participants with HS in our cohort were smokers (Table 1), which is in contrast to the prevalence studies from Australia and the UK. This suggests that HS is a complex disease with a number of prominent factors playing a role in the aetiopathogenesis. Finally, this study supports the previously reported prevalence data in Ghana.2 Paa Gyasi Hagan: Conceptualization (equal); investigation (lead); methodology (equal); project administration (lead); supervision (lead); writing – review and editing (supporting). Dorra Bouazzi: Formal analysis (equal); project administration (equal); writing – original draft (lead). Gideon Nyarko: Investigation (equal); validation (equal). Elsie Serwaa Dartey: Investigation (equal); validation (equal). Kojo Botsie Nunoo‐Ghartey: Investigation (equal); validation (equal). David Nkum: Investigation (equal); validation (equal). Prince Ansu: Investigation (equal); validation (equal). Joel Yiadom Boakye: Investigation (equal); validation (equal). Rune Kjærsgaard Andersen: Conceptualization (equal); project administration (supporting); software (lead); writing – review and editing (supporting). Jurr Boer: Conceptualization (equal); methodology (equal); supervision (equal); writing – review and editing (supporting). Gregor Jemec: Conceptualization (equal); methodology (equal); supervision (equal); visualization (equal); writing – review and editing (lead). Data not available due to privacy/ethical restrictions