This retrospective study was conducted after obtaining permission from the Institutional Ethical Committee. Our centre is located in the Udupi district of the state Karnataka. The patients visiting our centre are mostly drawn from neighbouring districts of Karnataka as well as Kerala. A total of 2219 consecutive patients, who underwent skin prick testing, between January 2011 to June 2014, as out patients or in patients in the Department of Pulmonary Medicine, were included in the study. The inclusion criteria included age between 15 and 75 years and established diagnosis of bronchial asthma and/ or allergic rhinitis [4,5]. Children, less than 14 years of age were not included as they might develop automatic remission beyond this age [6]. Patients who had taken short-acting oral antihistaminics, beta-blockers, steroids, tricyclic antidepressants or any other drug that could affect the test within one week prior to testing were excluded. Also, patients on long-acting oral antihistaminics within four weeks of testing and pregnant women were excluded [1,3,7].

A total of 64 antigens were used which included eight types of pollens, eight types of dusts, six types of fungi, eight types of insects, two types of danders, wool and 31 types of food items.

During the skin prick testing the skin was punctured on the volar aspect of the forearm, at 2 to 2.5 cm interval, with a calibrated lancet (1 mm) held vertically and lifted slightly to allow adequate entry of antigen beneath stratum corneum [8]. A positive histamine control and a negative buffered saline control were kept for every patient. At the histamine puncture site a wheal developed within 10 minutes. Evaluation of skin reactivity was done by calculating the mean diameter as (D + d)/2; where D = longest diameter and d = perpendicular diameter at the largest width of D after 15 minutes. If the mean wheal diameter was ≥3 mm than negative control (buffered saline), it was considered to indicate sensitisation to the allergen and, hence, a positive response. To rule out dermographism, which makes the test results difficult to interpret, the use of the negative control is required [9].

Out of 2219 patients, 1193 (53.8%) were males and 1026 (46.2%) were females. The mean age of the subjects was 41.47 (± 14) years. There were 740 (33.3%) patients diagnosed with bronchial asthma, 357 (16.1%) allergic rhinitis and 1122 (50.6%) had both bronchial asthma and allergic rhinitis. Majority (95.4%) of the patients were from state of Karnataka and the rest from Kannur and Calicut districts of Kerala. The district wise distribution of patients is shown in [Table/Fig-1]. In our study a total of 64 antigens were used per patient and; hence, a total of 142016 skin prick tests were done. The results of the skin prick test are shown in [Table/Fig-2,3].

Bronchial asthma and allergic rhinitis can coexist in the same patient or can develop one after the other [10]. Genetic, environmental and geographical conditions influence allergic sensitization, and subsequent development of symptoms [11,12]. Atopy is a very important risk factor for bronchial responsiveness and allergens can be precipitating factors even for sudden respiratory arrest [13,14]. Hence, identification of specific allergens which are most prevalent in the region is valuable for diagnosis and treatment of bronchial asthma and allergy rhinitis. Skin prick test is a commonly used method for detecting the implicated allergens and provides faster results when compared Radio Allegro Sorbent Testing (RAST) [9].

In our study, overall the most common offending allergen-group was insects followed by dust, grass and tree pollens, fungus and food allergens. Various studies have reported insects to be the most common offending antigens, with percentage ranging from 17.5% to 43.9% of the antigens studied [1-3]. Somewhat different results were reported, from a study done in Allahabad, Uttar Pradesh, on a relatively smaller cohort (50 patients), which showed dust mite (78%) followed by dust (66%) and insects (44%) as the implicated antigens [8].

Among the individual allergens, in our study, most common offending allergen was rice grain dust and the least common was chicken. In contrast, Kumar R et al., observed, in a study on aeroallergens, that the most common allergen was moth (33%); whereas, the least common was Ehretia (0.54%) [3]. Prasad R et al., in a study done in a medical college in Lucknow, found the pollen of Amaranthusspinosus to be the most common allergen (39.58%) [2]. This difference in various studies could be due to differences in study size and the geographical regions where they were conducted.

In our study, the highest percentage of skin positivity in the insects group was for rice weevil as well as grasshopper, followed by housefly and cockroach. Presence of protease allergens in the extracts obtained from the insects may also be the cause of allergy [15-17]. In contrast to our study, a study done by Kumar R et al., showed most common insect was moth followed by mosquito [3]. Patel A et al., from Gujarat has also reported moth as the most common insect allergen [1]. Agrawal RL et al., from Uttar Pradesh demonstrated cockroach as the most common offending insect [8]. Sarinho ECS et al., in a study from Brazil, conducted on adolescents, found cockroach as the most common allergen [18]. Also, in a study, done in Malaysia on 200 asthmatics, it was again noted that cockroach was the most common allergen demonstrating skin positivity, after house dust mites. Cockroach-derived allergens come from its saliva and faecal material [19]. It is obvious that different studies from different regions and countries are reporting varying results.

Rice grain dust, followed by house dust mite and house dust, were identified as the common dust allergens, in our study. Various studies have reported house dust while others have reported house dust mite as the most common dust allergen [8,20,21]. In general, house dust mite is a common cause of allergy worldwide [22].

Prosopis, argemone and eucalyptus were the three most common grass and tree pollen allergens observed in our study. A similar result was observed by Goyal M et al., in a study on 100 patients in Jaipur, Rajasthan, which revealed prosopis as the most common offending pollen [17]. In contrast, weed pollen, Ageratum, were observed as the most common pollen allergen among 918 patents of bronchial asthma and/or allergic rhinitis, in Delhi [3]. Amaranthusspinosus was the predominant offending pollen, reported in studies from Lucknow, Uttar Pradesh and Jalandhar, Punjab [2,23]. Varying distribution of pollen grains, among different regions of the country, may explain such different results [24].

The predominant fungus in our study were Aspergillus flavus followed by Aspergillus fumigates and Candida. Differing from our study, some studies have shown Aspergillus fumigatus as the most common fungus [2,8]. Study conducted in Jabalpur, on 180 poultry workers, showed predominance of Aspergillus niger sensitivity; whereas, study from Punjab reported Cladosporium herbarum allergen as the most common, again highlighting the regional variation in the results [23,25].

We observed that split red gram, split green gram, glycine max, coriander, pearl millet showed maximum percentage positivity to skin prick test, in the present study. A study testing for food intolerance, in patients with bronchial asthma in Delhi, by Kumar R et al., showed maximum intolerance to cow milk, casein, tiger nut and almond [26]. Further studies, testing various food allergens are required, in order to determine the sensitivity pattern predominant in different regions as per the food habits.

Our study will be useful in providing information on the pattern of allergen sensitization in this part of the country. The differences in skin positivity test results for various allergens in different regions of the country can be important for management of patients with allergies. Although, avoidance of the allergens may be difficult, it is one of the methods included in the management. Allergen-specific immunotherapy is other option, in selected cases, in addition to the standard treatment.

The study was hospital based and hence, referral bias becomes a limitation. Moreover, the results cannot be extrapolated to other parts of Karnataka as it is a large state with varied geography.

Among the allergen groups, insects and dusts elicited the highest percentage of skin-prick test positive results. Whereas, among all the individual allergens rice grain dust and house dust mite elicited highest percentage of positives.