The study was a cross-sectional population-based study. The data collection lasted for about 8 weeks, from 2^nd February to 29^th March 2019. Clearance from the Ethics Review Board of Babcock University, Ilisan-Remo (BUHREC044/19) was obtained. Written informed consent was also obtained from all respondents. There are no FDr studies in Nigeria whose prevalence could be used to determine the sample size. Using as a surrogate, the proportion of participants (13%) who had diarrhoea-predominant IBS in a previous Nigerian community-based study [10] and the Leslie Fischer’s formula (n=Z²pq/d², with confidence interval set at 95%, p=Proportion, q=1.0-p, normal deviate Z=1.96 and d=0.05), the minimum sample size required for the study was 174. Adjusting for missing or incomplete data entry with an expected response rate of 90% (0.9), increased the sample size to 193. The present study considered 515 subjects to increase its power.

A total of 515 adults, residents of Ilisan-Remo, Ogun State, Southwest Nigeria, were interviewed. The population of the community is slightly above 10,000 people. There are 51 major streets in the community, out of which 10 were initially randomly selected by ballot. Two additional streets were selected to complete the sample size. Adults (18-70 years) living in the households on each of the selected streets, who consented to participate in the study were interviewed by adequately trained research assistants.

Inclusion criteria: FDr was assessed with the Rome IV [6]. The subject needed to have loose or watery stools, without predominant abdominal pain or bothersome bloating, occurring in at least 25% of stools. The criterion must be fulfilled for the last 3 months with symptom onset at least 6 months before diagnosis. Subjects should also not meet the criteria for diarrhoea-predominant IBS. Since symptoms’ frequencies are rated from 0 to 100% with an interval of 10 in the Rome IV questionnaire, 30% cut was considered for the present study. Respondents who were positive for FDr were the cases while those who had no FDr were the controls. Subjects with diarrhoea occurring in at least 30% of stools lasting for at least three months who did not meet the other criteria for FDr were also evaluated.

Exclusion criteria: Pregnant women, those with confirmed diabetes mellitus, unintended weight loss, history of abdominal surgery, and rectal bleeding were excluded.

The participants completed a questionnaire containing demographic information such as age, gender, educational attainment; lifestyle factors including cigarette smoking, alcohol consumption, coffee intake; the Rome IV Functional Bowel Disorder questionnaire; the Beck Anxiety and Depression Inventories; the Early Trauma Inventory-Self Report; the PSQI; and the Short Form 12, version 2 Health Survey (SF-12v2) questionnaire. For ease of stool form assessment, a copy of the Bristol Stool Scale was shown to the respondents [11].

Psychological factors: Anxiety and depression were assessed with the Beck Anxiety Inventory (BAI) [12] and the Beck Depression Inventory-II (BDI-II) [13], respectively. Bremmer’s Early Trauma Inventory Self-report Short Form (ETISR-SF) [14] version was used for assessment of early life trauma exposure, while sleep quality was assessed with the PSQI [15]. These instruments have been adequately described in the published research protocol [9].

Health-related quality of life: The HRQoL of the participants was assessed by the Short Form-12, version 2 (SF-12v2). The SF-12v2 is a generic HRQoL instrument which measures the Physical Component Summary (PCS12) and the Mental Component Summary (MCS12) of subjects as well as their profile across 8 subscales {Physical Functioning (PF), Role Physical (RP), Bodily Pain (BP) General Health (GH), Vitality (VT), Social Functioning (SF), Role Emotional (RE), Mental Health (MH)} [16,17]. Each of the components is scored on a scale from 0 to 100 with a mean of 50 and a standard deviation of 10, where the higher scores represent better health.

Data were analysed with the IBM-Statistical Package for Social Sciences software (IBM SPSS Statistics for Windows, Version 22.0. Armonk, NY: IBM Corp, Chicago, IL. USA). Summaries of continuous variables were presented as mean±SD. The Independent Student t-test was used to compare means where necessary. Categorical variables were expressed as frequencies and percentages. The odds ratios of prospective risk factors of FDr were calculated with logistic regression. Variables with odds ratios (OR) >1 and p-value ≤0.05 were considered significant.

A total of 515 adults aged 18-70 years were included in the study. Ten participants were excluded due to improper filled questionnaires, so leaving 505 respondents. The respondents’ mean age was 32.7±12.9 years. There were 260 (51.5%) female subjects while the others were male. The majority of the subjects [448 (88.4%)] had at least secondary education, while the others had primary or no formal education 57 (11.3%) [Table/Fig-1].

FDr was found in 6 participants {1.2% (95% CI, 0.4%-2.4%)}. The mean age of those with FDr was lower than the controls (27.7±7.7 vs 39.8±13.0), though not statistically significant (p-value=0.346) [Table/Fig-1]. The number of participants with diarrhoea occurring in at least 30% of their stools for 3 months who did not fulfil the other criteria for FDr was 59 {11.7% (95% CI, 8.9%-14.3%)}.

The mean depression score of participants with FDr was higher than that of the controls with statistical significance (18.0±12.8 vs 8.2±9.5, p-value=0.021). There was no significant difference between the mean ETISR-SF and PSQI scores of participants with FDr and the controls [Table/Fig-1].

The mean SF-12v2 scale scores, except for vitality, were lower in subjects with FDr than the controls though only social functioning was statistically significant (p-value=0.003) [Table/Fig-2].

Functional diarrhoea has received little attention by researchers globally [3] and this is more severe in Africa. Authors could not found any data to compare the finding in Nigeria or other sub-Saharan African countries. International comparison of the prevalence of FDr is a bit difficult because different studies utilised varying diagnostic criteria [Table/Fig-3]. It has been shown that the Rome IV criteria have higher prevalence rates than the Rome III, largely because of the reduction of the cut-off of diarrhoea frequency from 75% to 25% [18].

Present study obtained a prevalence of 1.2% using the Rome IV criteria. Though this prevalence can be said to be low, there is a moderate prevalence of chronic diarrhoea in the same population (11.7%). In general, studies in the Western populations have shown higher prevalence rates compared to those conducted in the Asian populations [Table/Fig-3] [18-25]. For example, a population-based study that utilised the Rome II criteria in Canada [19] and another that utilised the Rome IV criteria in the USA [18] had prevalence rates of 8.5% and 4.9%, respectively while studies conducted in China [22] and South Korea [23] with the Rome II criteria produced prevalence rates of 1.5% and 0.8%, respectively. From the foregoing, it can be seen that the prevalence rate obtained in this study is comparable to those obtained in studies from Asia.

Few data are available on the risk factors of FDr [4]. Most of the available studies did not investigate the risk factors of FDr as a disease entity. Among all the possible risk factors examined in this study, only depression was found to be positively associated. It is uncertain whether this association implies causality since a person with FDr could develop depression while it is also possible for depression to induce FDr. A study from China [22] found FDr to be positively associated with increasing age and body weight but Authors did not find such association in the present study. Similar to the Chinese study [22], we found no significant association between FDr and other lifestyle factors such as cigarette smoking, alcohol consumption, and regularity of physical exercise.

Chronic diarrhoea has been noted to be associated with an increased rate of work absenteeism, physician visits and high socioeconomic burden [26] but few studies have evaluated the impact of FDr as a separate disease entity on the HRQoF in the general population. Nevertheless, Palsson OS et al., and Zhao YF et al., have separately reported that FDr negatively impacts the HRQoF of the sufferers [18,22]. In the present study, it was observed that persons with FDr generally had lower mean scores on the SF12v2 scales, though only social functioning was statistically significant. It is possible that social functioning was the most impacted among the variables because having to visit the toilet more often would constitute undue interruption to their social activities.

The strength of this study lies in the fact that it is a community-based study whose findings are representative of the characteristics of the disease in the general population. Since it seems to be the first of its kind in the Nigerian population, the findings would also serve as a reference for future related studies.

The major limitation of this study lies in the fact that the data collection instrument relies majorly on recall of bowel habits and several of the psychosocial factors considered and this may have affected the findings of this study. Nevertheless, Manning AP et al., observed that there is a close correlation between recalled and documented histories of bowel habits in more than 80% of cases [27]. Secondly, the findings may not be representative of the paediatric and adolescent population of the community because they were excluded from the study. Thirdly, since we considered only one community due to resource constraints, the findings may not be a fair representation of the epidemiological characteristics of FDr in every part of Nigeria. This is because functional gastrointestinal disorders do exhibit a wide variation in prevalence in communities [4,28].

The present study shows that there is a low prevalence of FDr in the community, though chronic diarrhoea is moderately prevalent. In addition to its negative impact on HRQoF, Authors also observed that FDr has a significant association with depression. These observations indicate that physicians who care for patients with FDr need to pay a close attention to their mental health and quality of life to obtain the best care outcomes. Due to the scarcity of data on the disease, further studies are desirable to clarify its epidemiology worldwide, in general, and in the sub-Saharan African population in particular.