- Top of page
- Material and methods
Background: The aim of this study was to estimate the prevalence of IgE-mediated allergy to Lepidoglyphus destructor and its clinical importance in Reykjavík, Iceland.
Methods: All Icelandic participants in the European Community Respiratory Health Survey in Reykjavík and suburbs were skin prick tested (SPT) for L. destructor. They also participated in a structured interview including questions about exposure to hay and symptoms related to hay exposure. Spirometry and methacholine tests were also performed.
Results: Altogether, 540 individuals underwent SPT with 12 allergens. Among them, 137 (25.4%) had positive skin tests, defined as at least one mean wheal reaction of ≥1 mm. By this definition, 34 (6.3%) were positive to L. destructor. These 34 individuals were significantly (P<0.001) more often allergic to D. pteronyssinus (24/34), grass (14/34), cat (13/34), dog (12/34), Alternaria (11/34), Cladosporium (9/34), horse (8/34), and olive (8/34) than those not allergic to L. destructor. Those SPT positive to L. destructor had a higher total IgE (geometric mean: 40.9 kU/l vs 12.3 kU/l, P<0.001) than those who were negative to L. destructor, but their lung function was comparable to that of the others. Asthma during the preceding 12 months or asthma ever suffered was not overrepresented among those SPT-positive to L. destructor. Individuals with symptoms associated with hay exposure were more often SPT positive to L. destructor than those not having symptoms (P<0.01).
Conclusions: In a random urban population, 6.3% showed IgE-mediated allergy to L. destructor. These were often polysensitized atopics with a high prevalence of clinical symptoms associated with exposure to hay.
Diseases related to exposure to hay dust have been known for centuries in Iceland (1). The first publication on respiratory symptoms related to inhalation of hay dust appeared in 1790. A few years later, another publication described a case of chronic obstructive lung disease as a consequence of long-lasting exposure to hay dust (1). In the second half of the 20th century, hay-related complaints were still common in Iceland, especially among farm workers (2).
In 1979, Cuthbert et al. were the first to report allergy to storage mites in Scottish farm workers exposed to hay and grain used to feed cattle wintered indoors (3). Subsequent studies of farmers in Finland, Sweden, the UK, and Denmark have confirmed the importance of storage mites in causing allergic symptoms among farm workers (4–7). Allergies to storage mites have also been reported to be a problem among grain handlers and bakers (8, 9), but others have not found an increased prevalence of allergy to storage mites in bakery workers (10, 11). Tee et al. concluded that storage mites were probably widespread in the general environment and that allergy to them among bakery workers was not only a consequence of exposure at work (10).
Several authors have reported positive results of skin prick tests (SPT) to Lepidoglyphus destructor in selected urban populations with atopic symptoms such as asthma and rhinitis (12–14). We are not aware of such study on a random sample of an urban population. Our previous experience had shown sensitization to L. destructor to be the most common cause of IgE-mediated allergy among Icelandic farmers (2). The aim of this study was to estimate the prevalence of IgE-mediated allergy to L. destructor in a randomly selected urban population and to assess its clinical importance.
- Top of page
- Material and methods
In this study, we used a cutoff limit for a positive SPT of ≥1 mm, which was the smallest positive skin response recorded in the study. In epidemiologic studies, positive SPT results have been expressed as wheal size from >0 to 5 mm or at least half the histamine wheal diameter. In a newly published study, a cutoff of >0 mm for positive results gave a more consistent relation to the corresponding specific IgE value than either a cutoff of ≥3 mm or the use of the mean wheal diameter (21). In our study, an SPT reaction of ≥1 mm to L. destructor had a good correspondence with the symptoms reported from hay dust (P<0.01).
Compared to results from other ECRHS centers, the mean total serum IgE in our study area is the lowest reported (22). The prevalence of positive SPTs in our area was also relatively low (22). Compared to other allergens, L. destructor is of importance even in the urban population of Iceland and should be included in a standard SPT panel.
How far these results reflect the situation in urban populations in other countries is uncertain. A surprisingly large number of participants in the study had been exposed to hay dust at some period in their lives. That is probably unique to the urban population in Iceland. Of those never exposed to hay dust, 5% were SPT positive to L. destructor, a figure higher than for half of the allergens tested in this study.
The hay harvest season is very short in Iceland, only 2 months, and rainy weather makes drying the hay difficult, often leaving wet pockets in the harvested hay.The average relative humidity of air at that season is 78–84%, a level at which the hay tends to equilibrate when stored in the barns (23). Storage mites flourish in such an environment. Nine-teen different species of storage mites have been described in the hay in Iceland, and L. destructor was found in 83% of all hay samples, sometimes in very high numbers (24).
In a previous study of farmers' families in two communities in Iceland, a third of the study population had some hay-related symptoms in the eyes and respiratory tract, and 38% of those with symptoms had positive SPT to L. destructor, with ≥2 mm as the cutoff limit for positive tests (2).
Although this study was carried out on a random urban population, 54% had had some previous history of exposure to hay dust. In Iceland, exposure to hay was very common among the urban population during the middle of this century because of farm vacations among the youngsters, especially boys. In many cases, this exposure was only sporadic and at an early age. Nowadays, horseback riding is increasing in popularity, with the horses mainly tended by men. This fact probably explains the more common exposure and greater prevalence of symptoms among men than women.
Being exposed to hay is a risk factor for sensitization to L. destructor, as seen in Table 2, even though the figures are significant only for those feeding horses, who thereby possibly experience the greatest exposure.
Our study found a relationship between symptoms and skin responses to L. destructor for all symptoms, and this result is in accordance with our earlier experience (2).
There was a strong correlation between skin responses to L. destructor and D. pteronyssinus, a finding which may express a cross-reaction between these allergens (25, 26) or multiple sensitization to different species of mites because of the home environment. No investigation has been carried out on the occurrence of mites in Icelandic homes.