Sir,
Extrinsic asthma, or allergic asthma, is the prevalent asthma phenotype frequently found in children and younger adults. Most patients with this form of asthma demonstrate an inherited allergic predisposition, although the sensitivity to individual allergens varies with individuals. In India, more than 20% of the population suffers from some form of IgE-mediated allergic disorder.[1] With a compatible clinical presentation, a positive skin prick test to one or a group of allergens firmly establishes the allergic nature of the disease. Sensitivity to certain agents is linked with severe disease. Hence, recognizing sensitivity to a particular allergen is important for treating such patients. Previous workers have postulated that the change in aerobiology over a sequential period due to climatic change may account for varying results in studies conducted at differing time frames.[2] Hence, knowledge of contemporary allergen sensitivity patterns in subjects of a particular geographic territory is vital to the practising clinician.
We undertook the RADIANT asthma study to assess the relation between specific aeroallergen sensitivity and the severity of airflow limitation in asthma. We also evaluated the asthma exacerbation rate with sensitization to different aeroallergens. We performed allergy skin prick test using allergens manufactured by Merck allergopharma. The study was a single-centre cross-sectional observational study. The study population comprised adult patients (aged >18 years) with GINA-defined asthma requiring step 4 therapy who were evaluated with a skin prick test for aeroallergen sensitivity. Pregnant and lactating ladies as well as patients with immunodeficiency states were excluded. A total of 76 asthmatic patients visiting the outpatient department of pulmonary medicine during the study period were included in the study. Among the 76 patients, 46 had concomitant allergic rhinitis also. The mean age of the study population was 36.88 years. The study population had 45 male patients (constituting 59.2% of the study population) and 31 female patients (constituting 40.8% of the study population.
Among the tested aeroallergens, sensitization to house dust (derp 1, derp 2), Aspergillus niger, A. fumigatus (Asp f2, Asp f3) and pigeon feather was associated with severe airflow obstruction and severe asthma (P-value of 0.022, 0.003, 0.029 and 0.026, respectively). The patients studied have had exposure to the agents to which sensitization was noted. Hence, they had asthma substantially driven by these exposures. Reactivity to A. niger was seen in 28% of patients with mild, 23% with moderate and 60% with severe airflow limitation. Sensitization to house dust was seen in 42.9% of patients with mild, 71.4% with moderate and 80% with severe airflow limitation. Sensitizations to other aeroallergens were not found to correlate significantly with the severity of rhinitis. The relation between allergen sensitization and the severity of asthma is shown in Table 1.
Table 1.
Relation between sensitization to aeroallergens and severity of asthma (only those agents with positive correlation shown)
| Allergen | Sensitization | FEV1 >80% | FEV1 50–80% | FEV1 <50% | Linear by linear association | P |
|---|---|---|---|---|---|---|
| House dust | Present | 6 (42.95) | 30 (71.4%) | 16 (80%) | 5.237 | 0.022 |
| Absent | 8 (57.1%) | 12 (28.6%) | 4 (20%) | |||
| Aspergillus fumigatus | Present | 5 (35.7%) | 15 (35.7%) | 13 (65%) | 4.756 | 0.029 |
| Absent | 9 (64.3%) | 27 (64.3%) | 7 (35%) | |||
| Aspergillus niger | Present | 4 (28.6%) | 10 (23.8%) | 12 (60%) | 6.979 | 0.008 |
| Absent | 10 (71.4%) | 32 (76.2%) | 8 (40%) | |||
| Pigeon droppings | Present | 11 (60%) | 34 (78.6%) | 12 (81%) | 4.976 | 0.026 |
| Absent | 3 (21.4%) | 8 (19%) | 8 (40%) |
Patients sensitized to Aspergillus species and pigeon feather dust had greater exacerbation rates (evaluated in the preceding 6 months prior to performing skin prick test) than patients who were not sensitized to either. We constructed a Kaplan–Meier plot [Figure 1] to assess the risk of exacerbation in patients sensitized to Aspergillus species, pigeon dropping and neither. It was seen that the highest probability of an exacerbation was in patients exposed to Aspergillus species. A moderate risk of exacerbation was seen in those sensitized to pigeon droppings and the least rates were observed in those sensitized to neither (P-value = 0.0310).
Figure 1.
Cumulative incidence of exacerbations on exposure to Aspergillus (A) or pigeon droppings (P) or neither (N) on Kaplan–Meier plot
There is evidence that high exposure to mite allergens adversely impacts asthma severity. Chronic exposure to naturally occurring lower levels of house dust mite (HDM) allergens might increase the severity of asthma. Langely et al. observed that subjects both sensitized and exposed to high levels of sensitizing allergen (HDM) had significantly lower FEV1 per cent predicted values, higher eNO values and more severe airway reactivity compared with subjects not sensitized and exposed.[3] Among the other allergens, fungal sensitization is associated with increased asthma severity, increased hospital admissions for exacerbations and poorer lung function.[4] The entity of severe asthma with fungal sensitization (SAFS) is characterized by severe asthma, fungal sensitization and the exclusion of allergic bronchopulmonary aspergillosis (ABPA).[5] High sensitization to pigeons and their relation to severe asthma have not been reported in many studies previously, even in studies that have been carried out in the same geographic location a few years ago.[6,7] This observation in our study may be attributed to the fact that there are a large number of multi-storey buildings in our geographical area that are heavily inhabited by pigeons. A similar report of pigeon sensitivity has been noted in a study from Navi Mumbai, which also has tall skyscrapers with pigeon inhabitance.[8]
Our study is unique in that we looked at a specific group of asthmatics with persistent lung function limitation and are on step 4 or above of GINA-defined therapy (with high-dose inhaled steroids plus long-acting β2 agonists plus montelukast). Previous studies on aeroallergen sensitization in asthmatics have looked at non-specific asthma cohorts.[9,10,11,12] We have also correlated the severity of airflow limitation and exacerbation rate with the aeroallergen sensitivity pattern.
In conclusion, sensitization to house dust, A. niger, A. fumigatus and pigeon feather was associated with severe airflow limitation in allergic asthmatics. A substantially higher proportion of patients with positive skin prick to these agents had an FEV1 of <50% predicted. Frequent asthma exacerbation was also noted in this group of patients, most profound in patients with Aspergillus sensitivity.
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Conflicts of interest
There are no conflicts of interest.
REFERENCES
- 1.Chandrika D. Allergic rhinitis in India: An overview. Int J Otorhinolaryngol Head Neck Surg. 2017;3:1–6. [Google Scholar]
- 2.Rajesh V, Dhanya E, Divya R, Augstine J. Aeroallergen sensitivity in subjects with nasobronchial allergy: Contemporary trends in Kerala. Indian J Chest Dis Allied Sci. 2022;64:45–7. [Google Scholar]
- 3.Langley SJ, Goldthorpe S, Craven M, Morris J, Woodcock A, Custovic A. Exposure and sensitization to indoor allergens: Association with lung function, bronchial reactivity, and exhaled nitric oxide measures in asthma. J Allergy Clin Immunol. 2003;112:362–8. doi: 10.1067/mai.2003.1654. [DOI] [PubMed] [Google Scholar]
- 4.Black PN, Udy AA, Brodie SM. Sensitivity to fungal allergens is a risk factor for life-threatening asthma. Allergy. 2000;55:501–4. doi: 10.1034/j.1398-9995.2000.00293.x. [DOI] [PubMed] [Google Scholar]
- 5.Fairs A, Agbetile J, Hargadon B, Bourne M, Monteiro WR, Brightling CE, et al. IgE sensitization to aspergillus fumigatus is associated with reduced lung function in asthma. Am J Respir Crit Care Med. 2010;182:1362–8. doi: 10.1164/rccm.201001-0087OC. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 6.Divya R, Jolsana A, Dhanya EK, Melcy C, Suramya AS, Rajesh V. Aeroallergen sensitivity pattern in poorly controlled asthmatics and its relation to asthma control in a tertiary care setting of central Kerala, India. J Clin Diag Res. 2019;13:OC22–s5. [Google Scholar]
- 7.Dhanya EK, Rajesh V, Jolsana A, Divya R, Melcy C, Suramya AS. Sensitivity pattern to common inhalant allergens in subjects with allergic rhinitis in Kerala. Eur J Pharm Med Res. 2019;6:584–7. [Google Scholar]
- 8.Mirchandani M, Siddhique I, Nair G. Allergen sensitization patterns in asthmatics in urban western India evaluated by skin prick test. Ind J Applied Res. 2020;10:15–6. [Google Scholar]
- 9.Koshak EA. Skin test reactivity to indoor allergens correlates with asthma severity in Jeddah, Saudi Arabia. Allergy Asthma Clin Immunol. 2006;2:11–9. doi: 10.1186/1710-1492-2-1-11. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 10.Chogtu B, Magaji N, Magazine R, Acharya PR. Pattern of allergen sensitivity among patients with bronchial asthma and/or allergic rhinosinusitis in a tertiary care centre of southern India. J Clin Diagn Res. 2017;11:OC01–4. doi: 10.7860/JCDR/2017/26973.10328. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 11.Kumar R, Sharan N, Kumar M, Bisht I, Gaur S N. Pattern of skin sensitivity to various aeroallergens in patients of bronchial asthma and/or allergic rhinitis in India. Indian J Allergy Asthma Immunol. 2012;26:66–72. [Google Scholar]
- 12.Acharya PJ. Skin test response to some inhalant allergens in patients of nasobronchial allergy from Andhra Pradesh. Allergy Appl Immunol. 1980;8:34–6. [Google Scholar]