Introduction

Bronchial asthma is a global health problem that affects all age groups. Asthma continues to impose a substantial burden on morbidity, healthcare utilisation, and quality of life [1]. A large-scale, nationwide, cross-sectional study from India reported the prevalence of self-reported asthma as 1.9%, with regional variations [2]. Asthma is a heterogeneous airway disease characterised by airway inflammation and variable airflow limitation, encompassing multiple clinical and inflammatory phenotypes. Allergen sensitisation, that is, atopy, can occur across all phenotypes. Patients with an atopic phenotype often respond better to corticosteroid therapy, and their symptoms may improve with allergen avoidance and immunotherapy [1]. Atopy can be diagnosed using the skin prick test (SPT) or by measuring allergen-specific IgE levels in serum. Among these, SPT is a simple, cost-effective, and specific method for detecting IgE-mediated type I hypersensitivity reactions [3–4].

The prevalence of sensitisation to environmental allergens varies across geographical areas. The Indian subcontinent, with its diverse geography and climate, provides a unique environment that may influence allergen exposure and sensitisation patterns among patients with asthma. Understanding regional sensitization profiles is important for identifying local triggers and tailoring individualised management strategies. Systemic corticosteroid therapy can modulate immune responses and potentially influence SPT results [3]. Therefore, studying steroid-naïve patients with asthma offers a clearer assessment of baseline allergen sensitisation.

Traditionally, asthma is considered a disease of larger airways. However, increasing evidence highlights the critical role of the small airways (internal diameter ≤ 2 mm) in their pathophysiology [5]. Conventional spirometry parameters primarily reflect large airway function and may fail to detect subtle abnormalities in the small airways. Respiratory oscillometry is a sensitive technique for assessing lung mechanics, particularly small airway function [5]. However, it remains unclear whether small airway dysfunction differs between patients with atopic and non-atopic asthma.

The primary objective of this study was to assess the frequency and pattern of aeroallergen sensitisation using SPT in newly diagnosed, steroid-naïve (defined as no prior systemic or inhaled corticosteroid use) adult patients with bronchial asthma. The secondary objective was to compare demographic characteristics, blood parameters, and lung function indices, including respiratory oscillometry, between patients with atopic and non-atopic asthma.

Materials and methods

Results

Baseline characteristics and sensitization profile

A total of 257 patients with bronchial asthma were screened for eligibility. Of these, 52 were excluded based on predefined criteria, and the remaining 205 patients met the inclusion criteria and were enrolled in this study. The detailed patient selection process is illustrated in Figure 1. The mean age of the cohort was 36.9 ± 12.2 years, and 59% were male. The mean body mass index was 24.1 ± 3.8 kg/m². The mean FEV₁% predicted was 57 ± 16. Concomitant allergic rhinitis was present in 58% (95% CI: 50.7–66.3) of patients. The median peripheral blood eosinophil count was 324 cells/µL (IQR: 215–541), and the median serum total IgE level was 432 IU/mL (IQR: 233–853). The prevalence of eosinophilic asthma was 54.6% (95% CI: 47.8–61.9).

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Figure 1. Flow diagram of patient selection.

Among the 205 patients, 69.8% (95% CI: 62.9–75.6) were sensitised to at least one aeroallergen, and a clinically significant SPT response was observed in 48.3% (95% CI: 40.6–55.0) of the patients (Table 1). The most common sensitisation was to HDM, observed in 47.8% of patients, followed by cockroaches (37.6%) and weed pollen (29.8%), respectively. Among the HDM species, Blomia tropicalis was the most prevalent (41.0%), followed by Dermatophagoides pteronyssinus (34.6%) and Dermatophagoides farinae (31.7%). Among weed pollens, Parthenium hysterophorus was the most common (23.4%), followed by Cynodon dactylon (16.1%) and Argemone mexicana (11.2%). Sensitization to any mold was observed in 21.0% of patients, with Aspergillus fumigatus being the most frequent (10.2%), followed by Aspergillus niger (8.8%), Alternaria alternata (7.3%), and Aspergillus flavus (6.8%). House dust sensitisation was observed in 22.4% of patients. Sensitisation to dog epithelium was low and observed in only 4.4% of patients.

Table 1. Distribution of sensitization against different allergens.

Allergens	n, (%)	95% CI (%)
Sensitization against house dust mites	98 (47.8)	40.5–54.6
Blomia tropicalis     SPT ≥ 2+	84 (41.0) 52 (25.4)	34.1–47.3 19.4–31.3
Dermatophagoides pteronyssinus     SPT ≥ 2+	71(34.6) 54 (26.3)	28.3–41.5 20.3–32.4
Dermatophagoides farinae     SPT ≥ 2+	65 (31.7) 45 (22.0)	25.4–38.0 16.3–27.6
House dust     SPT ≥ 2+	46 (22.4) 16 (7.8)	17.1–28.3 4.1–11.5
Cockroach     SPT ≥ 2+	77 (37.6) 47 (22.9)	30.7–44.4 17.2–28.7
Sensitization to dog epithelium     SPT ≥ 2+	9 (4.4) 1 (0.5)	2–7.3 0–1.4
Sensitization to weed pollen	61 (29.8)	23.4–36.1
Parthenium hysterophorus     SPT ≥ 2+	48 (23.4) 16 (7.8)	17.6–29.7 4.1–11.5
Cynodon dactylon     SPT ≥ 2+	33 (16.1) 8 (3.9)	11.2–21.0 1.3–6.6
Argemone mexicana     SPT ≥ 2+	23 (11.2) 4 (2.0)	6.8–15.6 0.1–3.8
Sensitization to molds	43 (21.0)	15.6–26.8
Aspergillus fumigatus     SPT ≥ 2+	21 (10.2) 3 (1.5)	6.3–14.6 0–.3.1
Aspergillus niger     SPT ≥ 2+	18 (8.8) 2 (1.0)	4.9–12.7 0–2.3
Alternaria alternata     SPT ≥ 2+	15 (7.3) 3 (1.5)	3.9–11.2 0–3.1
Aspergillus flavus     SPT ≥ 2+	14 (6.8) 2 (1.0)	3.9–10.2 0–2.3

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CI: confidence interval; SPT: skin prick test.

Discussion

This study evaluated the prevalence and patterns of aeroallergen sensitisation in steroid-naïve adult patients with newly diagnosed bronchial asthma. Approximately two-thirds of patients exhibited sensitisation to at least one aeroallergen, with indoor allergens more commonly implicated than outdoor allergens. HDM was the most frequently identified allergen, followed by cockroach. Serum IgE levels were significantly higher in atopic patients. However, peripheral blood eosinophil counts, the prevalence of allergic rhinitis, and lung function parameters did not differ significantly between the phenotypes.

The frequency and distribution of aeroallergen sensitisation among patients with bronchial asthma vary considerably across geographical regions in India [11–18]. The reported prevalence of aeroallergen sensitisation in asthma, with or without allergic rhinitis, ranges from 54% to 100% [11–18]. The prevalence of sensitisation has also been shown to vary across studies conducted at the same centre at different time points [11, 12]. The frequency of HDM sensitization in Indian studies has shown considerable variability, ranging from 11% to 74% [11–18]. A study from Maharashtra reported HDM as the most common allergen, with a prevalence of 49.9%, consistent with our findings [13]. Among HDM species, Dermatophagoides pteronyssinus and Dermatophagoides farinae are commonly reported as the predominant allergens [11–18]. Some studies have identified Dermatophagoides pteronyssinus as the dominant species [13, 15], whereas others have reported a higher prevalence of Dermatophagoides farinae [16, 18]. In contrast, our study found that Blomia tropicalis was the most common sensitising HDM. Blomia is a storage mite that proliferates in stored rice, grains, and flour, particularly under warm and humid conditions. Chhattisgarh is one of the leading rice-producing states in India, and local environmental and occupational exposures may explain the higher prevalence of Blomia sensitization in our cohort.

In our study, sensitization to cockroach allergens was the second most prevalent and was comparable to that reported in other Indian studies [16–18]. Sensitization to weed pollen varied widely across studies, with reported frequencies ranging from 14% to 54%, and in some cohorts, weed pollen was the predominant aeroallergen [11, 16, 17]. The variability in sensitisation to weed allergens across studies may be attributed to several factors, including geographic and climatic differences that influence pollen distribution, and heterogeneity in study populations. Our findings on Parthenium sensitization are consistent with a study from South India, which reported a prevalence of 28.2% [16]. Sensitisation to Cynodon has been reported to vary widely, ranging from 2% to 54% across studies [11–18]. The study from Maharashtra reported Cynodon dactylon as the most common weed pollen allergen (26.3%), exceeding the prevalence observed in our cohort [13].

The prevalence of house dust sensitization in Indian studies ranges from 4% to 67%, and the prevalence observed in our cohort falls within this range [11, 12, 14, 16–18]. Variability in sensitization to house dust across studies may result from differences in environmental and housing conditions, population characteristics, and the type and standardisation of allergens used for SPT, which may not accurately reflect the indoor environment of the study population. Sensitization to mold allergens among asthma patients has been reported to range from 5.9% to 19.6%, which is comparable to our finding of 21% [11–16].

We observed that aeroallergen sensitisation was more frequent among males, consistent with studies from Europe and North America [19, 20]. However, a study from Delhi, India, reported similar sensitisation rates between sexes [11]. In our cohort, the prevalence of allergic rhinitis did not differ significantly between the phenotypes, in contrast to other studies that reported a stronger association between allergic rhinitis and atopy [19, 20].

Atopic asthma is typically associated with T2 inflammation, characterised by eosinophilic inflammation, elevated serum IgE levels, and increased exhaled nitric oxide. Although non-atopic asthma may exhibit T2-high inflammation, it can also present with T2-low or mixed inflammatory profiles. In our cohort, peripheral blood eosinophil counts did not differ between atopic and non-atopic patients, whereas discordance in blood eosinophil counts between these phenotypes has been reported [11, 19]. We also observed that the prevalence of eosinophilic asthma did not differ significantly between atopic and non-atopic patients. Serum IgE concentrations vary widely across different ethnic populations. Sharma et al. [21] reported wide variation in serum IgE levels among Indian patients with asthma, ranging from 100 to 4,000 IU/mL. Our study demonstrated significantly higher serum IgE levels in patients with atopic asthma, consistent with findings from other studies [11, 19, 22].

Prior studies [11, 19, 20, 22] have examined differences in spirometric indices between atopic and non-atopic asthma. Some studies [19, 22] reported a significantly lower FEV₁/FVC ratio in non-atopic asthma. We observed a lower FEV₁/FVC ratio in atopic asthma, although the difference was not statistically significant. Consistent with our findings, previous studies [19, 22] have reported no significant difference in the severity of airflow obstruction, as assessed by FEV₁% predicted, between atopic and non-atopic asthma. However, Nieves et al. [20] reported that both FVC% predicted and FEV₁% predicted were significantly higher in atopic than in non-atopic asthma. Consistent with this, we also observed significantly higher FVC in atopic asthma, although the underlying mechanism remains unclear.

T2-high asthma is often associated with more pronounced small airway dysfunction [23]. To our knowledge, no prior study has directly compared oscillometry parameters between atopic and non-atopic asthma. Our study is the first to demonstrate that the severity and frequency of impairment in oscillometric parameters do not differ significantly between these two phenotypes. The mean z-scores for respiratory impedance, particularly markers of small airway dysfunction, were markedly elevated in both groups, indicating substantial impairment irrespective of atopic status, which may have limited the detection of intergroup differences.

This study was conducted at a single tertiary care centre with a hospital-based population, which may limit generalisability. In addition, only a selected panel of pollen allergens relevant to the local region was tested and may not represent the full spectrum of aeroallergens. Among oscillometric parameters, X5 tended to be lower (i.e., more negative) in patients with non-atopic asthma; however, this difference did not reach statistical significance. This observation may be influenced by the sample size and warrants further evaluation in larger samples.

In conclusion, the majority of adult patients with bronchial asthma were sensitised to at least one aeroallergen, predominantly indoor allergens, particularly HDM. Despite differences in immunopathogenesis between atopic and nonatopic asthma, impairments in oscillometric parameters, including small airway dysfunction and severity of airflow obstruction, do not differ significantly between them.