Type of study

This was a cross-sectional, descriptive study with an analytical component, involving prospective data collection conducted from June 1, 2024, to September 30, 2024.

Study setting

The study was conducted in carpentry workshops in Parakou, a city located in north-central Benin, 407 km from the economic capital, Cotonou. Parakou is the regional capital of northern Benin and had a population of 255,478 inhabitants in 2013, with a surface area of 441 km².

Study population

The study population consisted of all certified carpenters and apprentices working in the city of Parakou who were geographically accessible. Professionals who were present on the day of the survey and who provided free and informed consent were included. For participants under 18 years of age, additional informed consent was obtained from a parent or legal guardian.

The sample size was calculated using Schwartz’s formula:

where n is the sample size, p = 0.065, corresponding to the proportion of WRA among carpenters in Nigeria [8], q = (1 – p) = 0.935, α = 0.05 (type I error risk), corresponding to a Z_α value of 1.96 from the standard normal distribution, and i = 0.05 (acceptable margin of error). After adding a 10% allowance for non-response, the minimum required sample size was 102 carpenters.

Sampling technique

Due to the absence of a comprehensive list of carpenters in Parakou, the study was systematically proposed to all workers encountered in carpentry workshops on the days of data collection. In order to make sure that we can meet the carpenters at the workshops, we went there between 8 AM and 2 PM.

Dependent variable

The dependent variable was the diagnosis of WRA. It was defined based on the worker’s asthma status according to the following criteria: i) No asthma: no history of asthma and no asthma attacks triggered by carpentry work; ii) OA profile: no history of asthma prior to starting carpentry work, with asthma attacks occurring in the workplace and improving during periods away from work; iii) WAA profile: a history of asthma prior to starting carpentry work, with worsening symptoms at work and improvement during periods of inactivity; iv) Asthma unrelated to carpentry: no history of asthma before entering the profession, with onset of asthma after starting carpentry work, but with symptoms triggered by environmental factors unrelated to the workplace.

The WRA clinical profile included workers with either OA or WAA. These participants subsequently underwent peak expiratory flow (PEF) variability measurement and spirometry to confirm the asthma diagnosis. PEF variability was considered significant when there was an increase of PEF of at least 20% after bronchodilator administration compared to the pre-bronchodilator value [9]. Spirometry findings were consistent with asthma when a post-bronchodilation forced expiratory volume in one second (FEV₁) increased by at least 12% and at least 200 mL in absolute value.

Independent variables

The independent variables included sociodemographic characteristics (age, sex, ethnicity, place of residence, marital status, and level of education); medical history and lifestyle habits; occupational factors (exposure to wood dust, varnishes and glues used, use of personal protective equipment (PPE), presence of a mechanical ventilation system); asthma symptoms (cough, chest tightness, shortness of breath, wheezing) during the previous 12 months; symptoms of allergic rhinitis; findings from the pleuropulmonary examination (respiratory rate, prolonged expiratory phase, decreased vesicular breath sounds, wheezing, snoring rales); findings from the ENT examination (anterior rhinorrhea, including quantity and appearance, nasal mucosal edema, and inferior turbinate hypertrophy); level of asthma control; results of respiratory function tests (PEF variability and spirometry); and the impact of asthma on carpenter’s quality of life.

Data collection

Data were collected through anonymous individual interviews using a structured questionnaire. Asthma symptoms were assessed using the Occupational Asthma Screening Questionnaire-11 (OASQ-11) items [10]. Measurements of PEF variability and spirometry were performed only in workers with a WRA clinical profile.

Data processing and analysis

Data collected using the survey forms were double-entered into Epi Data software version 4.7.0.0 and analyzed using R software version 4.4.1. Quantitative variables were described using means (standard deviations) or medians (with interquartile ranges), depending on their distribution. Qualitative data were described using frequencies and percentages. Pearson’s chi-square test or Fisher’s exact test, as appropriate, was used to identify associations with the dependent variable. Crude odds ratios (cOR) with their 95% confidence interval (CI) and p-values were estimated using simple logistic regression. Variables with a p-value < 0.20 in bivariate analysis were included in the multivariable logistic regression model to estimate adjusted odds ratios (aOR), their 95% CI, and the p-values. The level of significance was set at 5%.

Ethical considerations

The study protocol was submitted to the Local Ethics Committee for Biomedical Research of the University of Parakou, which granted prior approval (REF: 776/2024/CLERB-UP/P/SP/R/SA). Authorizations were obtained from the Borgou Departmental Health Directorate and the Parakou Town Hall. Informed consent was obtained from all participants before inclusion, and data confidentiality was strictly respected.

Sociodemographic and professional characteristics of the carpenters included

Overall, of the 153 carpenters or apprentices that were identified in 117 workshops, 144 (94.1%) consented to participate in the survey. Of the participants, 103 (71.5%) were certified carpenters, and 41 (28.5%) were apprentice carpenters.

The mean age of the participants was 35.9 ± 12.1 years, with ages ranging from 16 to 60 years. The mean age was 41.5 ± 9.4 years among certified carpenters and 22.1 ± 4.1 years among apprentices, with a statistically significant difference (p < 0.001). All participants were male. A total of 102 (70.8%) carpenters were under 45 years of age, and 69 (47.9%) had attained secondary-level education (Table 1).

A personal atopy was found in 61 (42.4%) carpenters, including 42 (29.2%) with a history of allergic rhinitis and 23 (16.0%) with urticaria (Table 2). A family atopy was reported by 15.3% of them. A family history of asthma was reported by 24 (16.7%) carpenters, and 5 (3.5%) were known to have asthma before entering the profession.

In 94.4% (136/144) of cases, varnish was used as a finishing product, adhesives in 93.8% (135/144) of cases, and paints in 70.1% (101/144). Of the 144 carpenters surveyed, 103 (71.5%) worked in an environment considered confined, while 41 (28.5%) worked in a well-ventilated environment. Among them, 14.6% (21/144) always wore a mask, 19.4% (28/144) often wore one, 38.9% (56/144) sometimes wore one, and 27.1% (39/144) never wore one. There were 101 (70.1%) workers who wore surgical masks, whereas only 4 (2.8%) wore filtering facepiece particles (FFP3).

Prevalence and factors associated with work-related asthma

A WRA profile was identified in 10.4% of cases (15/144), including 10 cases of OA (95% CI: 3.8–12.3) and 5 cases of WAA (95% CI: 1.5–7.9), representing 6.9% and 3.5% of carpenters, respectively (Figure 1). Violent coughing fits lasting several minutes, and chest tightness were reported in 93.3% and 86.7% of cases, respectively (Figure 2).

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Figure 1. Flowchart of carpenters surveyed from June to September 2024. PEF: peak expiratory flow.

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Figure 2. Main respiratory symptoms suggestive of ALT among carpenters surveyed in Parakou in 2024 (N = 15).

The median duration of symptoms was 66 months [interquartile interval (IQR): 12–216] among certified carpenters and 24 months (IQR: 12–120) among apprentices. These symptoms were preceded by occupational rhinitis in all 15 workers with a WRA profile. After assessment of PEF variability and spirometry, asthma was confirmed in 7 (46.7%) of the 15 workers who presented clinical signs suggestive of WRA.

After simple and then multiple logistic regression, the factors associated with WRA were a history of allergic rhinitis (aOR = 3.90; p = 0.033) and urticaria (aOR = 8.21; p = 0.002) (Table 3).

Management and impact of the disease

None of the carpenters with a clinical profile of WRA had medical follow-up, and the costs associated with management were covered by the workers themselves. Asthma was well controlled in 53.3% (8/15) of cases, partially controlled in 26.7% (4/15), and uncontrolled in 20% (3/15).

Among the 103 certified carpenters surveyed, 6 (5.8%) were registered with the National Social Security Fund (NSSF), and 5 (83.3%) of them had paid their contributions.

Regarding the impact of the disease, it was considered to have a strong impact on productivity and periods of distraction in the same proportion, namely 13.3% (2/15). A moderate impact was reported in 40% (6/15) of cases for productivity, 26.7% (4/15) for periods of distraction, and 20% (3/15) for quality of social life.

Conclusion

This prospective study of carpenters working in the city of Parakou showed that one in ten workers had a profile suggestive of WRA. The frequency of clinical findings consistent with OA was twice that of WAA. Measurement of instantaneous PEF variability and spirometry confirmed the diagnosis of asthma in nearly half of the carpenters with suggestive symptoms. The risk of having a clinical presentation suggestive of WRA was significantly higher in individuals with a history of allergic rhinitis or urticaria, as well as a family history of atopy or asthma, according to bivariate analysis. Symptomatic carpenters mainly reported a moderate impact of their symptoms on work performance and leisure activities. None of them were under medical supervision, and self-medication was common practice.