Prevalence of asthma and other allergic conditions in adults in Khuzestan, southwest Iran, 2018

The study was conducted in the Khuzestan Province, southwest of Iran, located at the geographical coordinates of 31.33 ° N and 48.69 ° E. The Khuzestan Province shares border with Iraq and the Persian Gulf, which is the center of oil and gas production in Iranian [19]. The area of the Khuzestan Province is 64,057 km² and, with a population of 4,710,506 people, it is considered as the fifth-largest populated region of Iran. The capital of the Khuzestan Province is Ahvaz City [19].

This cross-sectional study was conducted during September 2017 to February 2018 on the adult population of the Khuzestan Province. The study was carried out in 24 counties of Khuzestan through sampling from 27 cities and 17 villages. The inclusion criteria were male or female from 20 to 65 years of age and giving personal consent for participation in the study. Exclusion criteria were individuals with specific illnesses, disabilities, and/or a mental state, and dementia at the time of study that prevented them from co-operating.

According to a similar study by Mehrabi et al., which estimated the prevalence of asthma in adults aged 15–65 years in Kurdistan to be 0.023 [20] and the National Census of 2016 which reports the population of the Khuzestan Province as 4,710,509 people, and the following formula, this research considered a sample size of 2600 people. Drawing upon the effect size 2, the sample size was obtained as 5200 respondents. Taking into account that approximately 10% of the respondents might not respond, we calculated the final sample size as 5720.

In this study, two-stage cluster sampling was used. In the first stage, all clusters in Khuzestan Province were selected. In the second stage, 143 clusters were selected by random systematic sampling from the whole cluster, taking into account the probability proportional to their size. The number of clusters in urban and rural areas was selected based on their population’s proportion to the population of Khuzestan Province. The list of census enumeration areas, population and geographic map of each cluster were prepared through correspondence with the Iranian Statistics Center and the latest census data (2017). At the end, 143 clusters each with a cluster size of 40 persons were selected. Each cluster included 8 men and 8 women aged 20 to 29 years old, 8 men and 8 women in the range of 30–44 years old, and 4 men and 4 women aged 45–65 years.

After receiving the necessary trainings, enumerators began sampling. They were handed maps of selected clusters and referred to the address of each cluster from the southwest point of that cluster in the clockwise direction. For each cluster, sampling was carried out until 40 respondents agreed to participate.

Of each family, not more than one person was selected for any age group, and if there were more than one person in a family for a certain age group, one was chosen among those whose day and month of birth were closer to the day of the survey. Questioning was done in the afternoons and holidays with the consent of the respondents.

The instrument for studying the prevalence of asthma and asthma symptoms was the ECRHS questionnaire, [21] which was previously used in domestic studies of standardization [7] and localization. The ECRHS questionnaire is the standard tool used in the survey of “the European Respiratory Society” in 48 centers in 17 European countries and 5 non-European countries between 1990 and 1995 in adults aged 20–44 [21].

In the ECRHS, asthma symptoms include: Wheezing in the past 12 months, wheezing with shortness of breath in the last 12 months, wheezing in the absence of cold during the past 12 months, feeling tightness in the chest while waking up in the past 12 months, nocturnal cough and dyspnea attacks in the last 12 months, a history of asthma attack in the last 12 months, recent anti-asthma medication, and nasal allergies.

Based on the ECRHS questionnaire, current asthma is defined as recently taking anti-asthma medication or having an asthma attack in the last 12 months. People with asthma-like symptoms are those individuals who have at least one symptom of asthma including wheezing, waking up with a feeling of tightness in the chest, waking up with dyspnea and coughing attacks in the last 12 months [21].

The questionnaire included questions about age, gender, education level, marital status, employment status, active smoking, passive smoking, quantity of cigarettes smoked, duration of smoking, physician-confirmed asthma (Do you have asthma (confirmed by doctor)?), allergic rhinitis, airway hyperresponsiveness and eczema condition.

In relation to the measurement of the prevalence of “airway hyperresponsiveness”, a multi-choice question was asked: Which of the following irritates you and starts symptoms such as shortness of breath, cough, sneezing, runny nose, itching of the eyes, red eye and the hives? pollen, dried plants, cat, dog, bird, cosmetics, spray, colognes, insecticides, rubber gloves, metal and jewelry, home dust, air pollution, exercise, nervousness, cold weather, humidity, cool air from a cooler, sweeping and any other substance (food, medicine and plant) that the person expresses.

Asthma is an inflammatory disease affecting the airways of the lungs and leaving long-term impacts on the patient [22]. The characteristics of the disease include: recurring symptoms, reversible airflow obstruction, and bronchospasm. The symptoms of this disease include wheezing, coughing, chest tightness, and shortness of breath [23].

Rhinitis is referred to inflammation and irritation of the mucous membrane which is inside the nose. The typical symptoms of rhinitis are a stuffy and runny nose and sneezing. This inflammation type is the result of exposure to bacteria, viruses, irritants or allergens [24].

Airway hyperresponsiveness is an increased sensitivity of the airways to a constrictor or agonist inhaled by the patient, a steeper slope of the dose-response curve, and a bigger maximal reaction to the agonist [25].

Eczema is referred to a group of ailments that leads to skin inflammation. The characteristics of these ailments are itching, red skin and a rash [26].

Considering that the results were obtained for 24 countries and were to be generalized to the total population of 20–65 years living in Khuzestan Province, all cities and villages were given weights. This means that each sample represents several people.

The total weight is obtained from the inverse multiplication of two weights: one is the weight associated with the cluster selection, and the other is the weight of each sample from the clusters. Total weight was obtained using a formula. In the formula, N_p is the total number of clusters in Khuzestan Province and n_p is the number of selected clusters (143 clusters). N_c and n_c are the total population of 20 to 65 year olds and the sample size in each cluster, respectively.

In the study, 5720 questionnaires were distributed of which 5708 were returned. Some of the variables such as education level and active smoking were non-response. The mean ± SD age of the respondents in the study was 34.5 ± 11.8 years (95% CI: 34.2–34.8). The proportion of men was 50.7% and women were 49.3%. The majority of the respondents held high school and associate’s degrees (37.9%), were married (62.0%), lived in urban areas (87.4%) and were employed (53.2%). The prevalence of smoking in the age group of 20 to 65 years was 15.7%. The average smoking rate was 18.1 ± 9.3 (95% CI: 16.6–19.7) cigarettes a day and the mean smoking duration was 14.1 ± 9.0 years (95% CI: 12.8–15.4). More details about the demographics of the respondents are shown in Table 1.

In the study, the prevalence of current asthma was 8.5% and asthma-like symptoms were 19%. The most common symptoms of asthma were nocturnal cough (13.6%), chest tightness (12.3%) and wheezing (13.1%). The prevalence of AR, eczema and airway hyperresponsiveness was 27.2, 10.7, and 38.7%, respectively (Table 2).

The results of bivariate analysis showed that the prevalence of current asthma, asthma-like symptoms, and all signs of asthma include: wheezing, wheezing with dyspnea, wheezing in the absence of colds, chest tightness, nocturnal dyspnea, nocturnal cough, asthma attack, medications for asthma and physician-confirmed asthma were not different in men and women (P-value> 0.05). However, AR, airway hyperresponsiveness and eczema were more prevalent in women (P-value< 0.05) (Table 2).

The prevalence of current asthma, asthma-like symptoms, all signs of asthma and physician-confirmed asthma in the age group of 45 to 65 years were significantly higher compared to other age groups (P-value< 0.05). Meanwhile, AR were more prevalent in young people aged 20–29 years (P-value < 0.05) (Table 3).

The prevalence of airway hyperresponsiveness among people with higher education is higher than others (P-value < 0.05). In contrast, the prevalence of asthma-like symptoms, wheezing with dyspnea, wheezing in the absence of colds, chest tightness, nocturnal dyspnea and nocturnal cough were significantly higher among illiterate people than others (P-value< 0.05)(Table 4).

Current asthma, wheezing with dyspnea, wheezing in the absence of colds, nocturnal cough, asthma attacks and medications for asthma were more prevalent in urban areas compared to rural areas (P-value < 0.05).It is worth to point out that the prevalence of current asthma, asthma-like symptoms, wheezing, nocturnal cough, medications for asthma and physician-confirmed asthma were significantly higher in smokers than non-smokers (P-value < 0.05). Moreover, AR, airway hyperresponsiveness and eczema among smokers were more prevalent (P-value< 0.05) (Table 5). The results of the adjusted model confirm these findings, except for relationship between signs of asthma and education (Table 6).

Figures 1 to 4 shows the prevalence of current asthma and other allergic conditions in different counties of Khuzestan Province. As regards the prevalence of current asthma, Ahvaz, Dasht-e Azadegan, Khorramshahr, Dezful, Gotvand and Bagh-e Malek, reported the highest prevalence rate (Fig. 1). With regard to the prevalence of AR, the counties of Shush, Dasht-e Azadegan, Masjed Soleyman and Ramshir were the most prevalent (Fig. 2). Also, among different counties, Ahvaz, Dasht-e Azadegan, Dezful, Masjed Soleyman and Ramhormoz had the highest prevalence of airway hyperresponsiveness (Fig. 3). Finally, the counties of Ahvaz, Dezful and Ramshir, had the highest prevalence of eczema (Fig. 4).