2016 Volume 58 Issue 1 Pages 7-15
Objectives: The aim of this estudy was to investigate the influence of allergen exposure levels and other risk factors for allergic sensitization, asthma, and bronchial hyperresponsiveness (BHR) in workers exposed to laboratory animals. Methods: This was a cross-sectional study performed at two universities, 123 workplaces with 737 subjects. Dust samples were collected from laboratories and animal facilities housing rats, mice, guinea pigs, rabbits, or hamsters and analyzed by enzyme-linked immunosorbent assay (ELISA) to measure allergen concentrations. We also sampled workplaces without animals. Asthma was defined by both symptoms and BHR to mannitol. The concentrations of allergens were tested for association with a skin prick test, respiratory symptoms, spirometry data, and BHR. This multivariate analysis was performed by using Poisson regression to estimate the relative risk (RR) for the exposed group. Results: Our sample comprised students and workers, with 336 subjects in the nonexposed group and 401 subjects in the exposed group. Sixty-nine subjects (17%) had positive results in the skin prick test for animal allergens in the exposed group; in the nonexposed group, 10 subjects had positive results (3%) (p<0.001). Exposure to laboratory animals over 2.8 years was associated with atopic sensitization (RR=1.85; 95% confidence interval: 1.09–3.15; p=0.02). Allergen concentration was not associated with sensitization, asthma, or BHR. Conclusion: Exposure to laboratory animals was associated with atopic sensitization. However, we did not find a cutoff allergen concentration that increased the risk for sensitization. Duration of exposure seems to be more relevant to sensitization than concentration of allergens in dust.
(J Occup Health 2016; 58: 7–15)
Workers exposed to laboratory animals have a high risk of developing allergic reactions1, 2). Rats and mice are the most common etiology of laboratory animal allergy because they are the most commonly used animals in research3). The high prevalence of this condition became evident from epidemiological cross-sectional studies conducted in the 1980s1, 4). Eleven to 44% of individuals who work with laboratory animals have reported allergic symptoms. These symptoms can range from skin reactions, nasal congestion, rhinorrhea, sneezing, and conjunctivitis, to severe asthma. Allergic rhinitis and allergic conjunctivitis symptoms are the most commonly reported symptoms. Among workers who become symptomatic, 4 to 22% have occupational asthma2).
In a cohort study of 342 laboratory animal workers, quantitative analyses of exposure demonstrated a dose-response relation between the intensity of exposure to skin symptoms and skin prick tests. Intensity of exposure (divided into 4 categories) was evaluated by quantification of rat urinary aeroallergen. Exposure-response relations for symptoms were observed among sensitized workers, and for chest and eye/nose symptoms, they were not as clear as for skin symptoms. Two exposure indices were created: one based on the weekly duration of exposure to rats and one based on the product of the rat urinary aeroallergen concentration and the weekly duration of exposure to rats. No clear exposure-response relations were detected for the weekly duration of exposure or the product of concentration times duration5).
Data on a 4- to 9-year-old inner-city asthmatic population demonstrated that an exposure-sensitization relationship exists for mouse allergen like that for cockroach allergen and that the highest risk for sensitization occurs when atopic children are exposed to higher levels of allergen. A concentration of 1.6 mg/g or higher of mouse allergen in dust was shown to be a level of allergen exposure that increased the risk of developing allergies and respiratory symptoms6).
In an attempt to identify a cutoff value for rat allergen exposure that was associated with increased risk for respiratory symptoms, 113 workers exposed to laboratory animals were enrolled in a cross-sectional study performed from September 1997 to July 1998. The prevalence of sensitization to rat allergen was 12%; however, airborne rat allergen levels were not related to symptoms in workers7). Therefore, there is still a need to define the existence of threshold exposure levels in different forms of occupational allergen exposures.
Thus, we investigated the role of allergen exposure levels and other worker characteristics as risk factors for allergic sensitization, asthma, and bronchial hyperresponsiveness (BHR) in workers exposed to laboratory animals.
This was a cross-sectional study conducted at two universities, the University of São Paulo at Ribeirão Preto (USP-RP) and the State University of Campinas (UNICAMP), São Paulo state, Brazil. Sample selection and the study protocol have been previously described8). Study subjects were workers exposed to laboratory animals (exposed group) and those without such exposure (nonexposed group). Data were collected in loco, i.e., in the workplace, from September 16, 2010, to February 10, 2012. All procedures were performed on Wednesdays, Thursdays, and Fridays, thus allowing lung function tests to act as possible indicators of the workweek effect.
Laboratories and workplaces were randomly selected from the facilities, and 123 workplaces were included in this study, with 56 workplaces belonging to the nonexposed group (336 subjects) and 67 workplaces belonging to the exposed group (401 subjects). At least 90% of the subjects in each workplace consented to participate; the overall consent and participation rate was 95%8). The study was reviewed and approved by the Ethics Committees of both institutions: Medical School of Ribeirão Preto, University of S. Paulo (protocol number 9428/2009), and the School of Medical Sciences, UNICAMP (protocol number 779/2009). Written informed consent was obtained from all subjects after reading and discussing the protocol individually.
QuestionnaireA self-administered questionnaire with 97 questions was used to inquire about respiratory, nasal, ocular, and skin symptoms and personal history of allergic diseases, smoking, and pet owning. The questionnaire items also included job characteristics, such as the duration of working with laboratory animals, job titles, job contents, frequency of contact with laboratory animals, time spent handling animals, species, use of protective equipment, and knowledge about animal-induced allergies, asthma, or rhinitis. To assess symptoms, we used questions from the European Community Respiratory Health Survey questionnaire, which has been translated into Portuguese, adapted to the Brazilian lexicon, and validated9, 10).
Skin prick testSkin prick tests (SPTs) were applied according to the recommendations of the European Academy of Allergology and Clinical Immunology11). All subjects refrained from taking antihistamine drugs for 15 days prior to SPT. A wheal diameter of at least 3 mm was considered positive in the absence of a reaction to physiological saline solution and in the presence of a positive reaction to histamine. The allergens included environmental allergens (common allergens, including Dermatophagoides pteronyssinus, Dermatophagoides farinae, Blomia tropicalis, Felis domesticus, Canis familiaris, Blattella germanica, Periplaneta americana, Alternaria alternata, Cladosporium herbarum, Aspergillus fumigatus, and mixed grass) and extracts from animals (the rat, rabbit, mouse, hamster, and guinea pig). These were called occupational allergens.
SpirometryLung function was measured using a Koko spirometer and its software (PDS Instrumentation, Inc., Louisville, Colorado, USA), which were calibrated daily. Measurements were performed in the sitting position with the subjects wearing a nose clip. At least 3 technically satisfactory maneuvers were attempted for each participant. If it was not possible to obtain at least 3 technically satisfactory maneuvers after 8 attempts, lung function testing was stopped12). The reference values of Crapo et al.13) were used.
Bronchial challenge test with mannitolDry powdered mannitol (Aridol) was supplied in kit form (Pharmaxis Ltd., New South Wales, Australia), which contained 1 empty capsule (0 mg), capsules containing 5, 10 and 20 mg, and 15 capsules containing 40 mg (cumulative dose of 635 mg). The challenge began with the empty capsule, followed by inhalation of 5, 10, 20, 40, 80, 160, 160, and 160 mg dry powdered mannitol. Forced expiratory volume in one second (FEV1) was measured 60 seconds after every inhalation. This procedure was repeated for each dose step until a 15% fall in FEV1 was achieved or the cumulative dose reached 636 mg, and a 15% decrease in FEV1 to 635 mg or less was regarded as a positive response indicanting BHR14).
Dust samplesFloor dust samples were collected in animal facilities and in laboratories without animals. Dust from one square meter was collected for 2 minutes15) using a vacuum cleaner (Arno Nitro, São Paulo, Brazil) equipped with a fiberglass filter with a pore size of approximately 1 µm (Indoor Biotechnologies Inc., Charlottesville, VA, USA). The amount of dust varied in different workplaces. The amount was compared between groups, and concentrations of allergen were expressed in relation to dust weight. Filters were weighed before and after sample collection. Loaded filters were transported separately packed and stored in a refrigerator (2 to 8°C) until measurements of mite allergen (Der p1), mouse allergen (Mus m1), and rat allergen (Rat n1) by using enzyme-linked immunosorbent assay (ELISA)16,17).
Variables:
Groups: The exposed group consisted of subjects engaged in experimental studies, including technicians, students, and researchers. The nonexposed group consisted of management employees, students, secretaries, computer technicians, car drivers, and others who had no contact with laboratory animals and who worked in a building with no animals. For more details on characteristics of groups and subjects, refer to Ferraz et al8).
Confirmed asthma: An individual was considered an asthmatic subject if he/she exhibited BHR and had experienced symptoms of wheezing, tightness of the chest during the night, or dyspnea during the day or at night in the previous 12 months.
Wheezing: Current wheezing was defined by a positive answer to the question: Have you had wheezing or whistling in your chest any time in the last 12 months?
Rhinitis: An individual was considered to have rhinitis if he/she had experienced symptoms of runny or blocked nose when they did not have a cold in the last 12 months.
Daily work hours: This variable was defined by the question: What are your daily work hours? Results were categorized into two categories: 8 hours or more and less than 8 hours.
Exposure years: This variable was the duration of exposure calculated from the date of beginning activities for the job. Results were categorized according to the median into two categories: more than 2.8 years (above median) and 2.8 years or less.
Past exposure to laboratory animals: This variable was defined by the question: In the past, did you work in places with animals (laboratories or animal rooms)?
Pet ownership: This variable was defined by the question: In the last 12 months, have you had pets at home?
Smoking: This variable was defined by two questions: Have you ever smoked for more than 1 year? If yes, have you smoked in the last 30 days?
Statistical analysisUnivariate analysis with the chi-square test was used to compare prevalence estimates between groups (exposed versus nonexposed group), and an unpaired two-tailed Student's t test was used to compare allergen concentration between exposed and nonexposed groups.
For the exposed group, relative risk was estimated by using a modified Poisson regression approach, i.e., Poisson regression with a robust error variance18). Model was adjusted by using the PROC GENMOD procedure in the SAS Software, version 9.2. Analyses were performed to test associations between characteristics of exposure and primary outcomes variables. Exposure characteristics were allergen concentration, pet ownership, institution, daily work hours, exposure years, job, and past exposures. Primary outcomes were sensitization to occupational allergen, BHR-confirmed asthma, and BHR (with or without asthma symptoms).
In order to investigate cutoff allergen concentrations related to sensitization, symptom, and BHR, receiver operating characteristics (ROC) analyses were performed19) with estimation of the area under ROC curve.
Data from 737 subjects, 336 subjects in the nonexposed group and 401 in the exposed group, were analyzed. The mean age was 32.8 ± 10.5 years, and there was no difference in age between the groups (p=0.089). Female predominance was observed, with 440 subjects (59.7%) being female. One-hundred twenty-three dust samples were evaluated for allergen concentration: 56 from the exposed group and 67 from the nonexposed group.
The prevalence of positive results in the skin prick test for each occupational allergen and comparative clinical and laboratory data for the groups are shown in Table 1. We found 69 subjects (17.2%) with positive skin test for occupational allergens in the exposed group and 10 subjects (3.0%) with positive skin test in the nonexposed group (p<0.001). For common allergens, 335 cases (45.4%) were positive, and there was no difference between groups. Rat and mouse allergens were the most common cause of a positive skin test, and the differences were significant between the groups (Table 1).
| Total (n=737) | Nonexposed group (n=336) | Exposed group (n=401) | p | |
|---|---|---|---|---|
| Positive skin prick test | ||||
| Common allergen(s) | 335 (45.4%) | 159 (47.7%) | 176 (44.0%) | 0.231 |
| Occupational allergen(s) | 79 (10.7%) | 10 (3.0%) | 69 (17.2%) | < 0.001 |
| Rat | 48 (6.5%) | 2 (0.6%) | 46 (11.4%) | < 0.001 |
| Mouse | 45 (6.1%) | 6 (1.8%) | 39 (9.8%) | < 0.001 |
| Rabbit | 18 (2.4%) | 6 (1.8%) | 12 (3.0%) | 0.290 |
| Guinea pig | 10 (1.4%) | 2 (0.6%) | 8 (2.0%) | 0.102 |
| Hamster | 11 (1.5%) | 3 (0.9%) | 8 (2.0%) | 0.219 |
| Spirometry | ||||
| Normal | 705 (95.7%) | 323 (96.1%) | 382 (95.3%) | 0.815 |
| BHR to mannitol* | ||||
| Positive test | 94 (13.0%) | 39 (14.3%) | 55 (15.0%) | 0.435 |
| BHR-confirmed asthma | 72 (9.7%) | 31 (9.2%) | 41 (10.2%) | 0.648 |
| Wheezing | 156 (21.1%) | 68 (20.2%) | 88 (21.9%) | 0.545 |
| Rhinitis | 326 (44.2%) | 149 (44.3%) | 177 (44.1%) | 0.846 |
Data are expressed as n (%). BHR: bronchial hyperresponsiveness. Occupational allergens: rat, rabbit, mouse, hamster, and guinea pig. Wheezing: positive answer to the question: Have you had wheezing or whistling in your chest any time in the last 12 months? Rhinitis: An individual was considered to have rhinitis if he/she had experienced symptoms of runny or blocked nose when he/she did not have a cold in the last 12 months.
Table 2 shows the allergen concentration in dust (Der p1, Mus m1, and Rat n1). Higher levels were detected in the exposed group workplaces as compared with the nonexposed group workplaces. Tables 3, 4, and 5 show data for the exposed group and describe the assessment of risk factors for the main study outcomes: occupational sensitization, asthma, and BHR, respectively. These data indicate that duration of exposure is a significant risk factor for sensitization (Table 3). For asthma, an association with past exposure to laboratory animals was detected (Table 4). No significant risk factor was detected in association with BHR (Table 5).
| Allergens | Nonexposed group (56 workplaces) | Exposed group (67 workplaces) | p* |
|---|---|---|---|
| Mite (Der p1), µg/g of dust | 0.042 ± 0.098 | 0.085 ± 0.189 | <0.0001 |
| Mouse (Mus m1), µg/g of dust | 1.307 ± 4.464 | 12.412 ± 20.899 | <0.0001 |
| Rat (Rat n1), µg/g of dust | 0.197 ± 0.353 | 9.559 ± 20.478 | <0.0001 |
| Variables | Univariate analysis | Adjusted analysis | |||||||
|---|---|---|---|---|---|---|---|---|---|
| Categories* | RR | 95% CI | p value | RR | 95% CI | p value | |||
| Concentration of dust mite allergen | Continuous | 0.51 | 0.13 | 2.05 | 0.34 | 0.28 | 0.06 | 1.31 | 0.11 |
| Concentration of mouse allergen | Continuous | 1.00 | 0.99 | 1.01 | 0.86 | 1.00 | 0.99 | 1.01 | 0.92 |
| Concentration of rat allergen | Continuous | 1.01 | 1.00 | 1.01 | 0.20 | 1.01 | 1.00 | 1.02 | 0.11 |
| Pet ownership | Yes (n=256) vs. no (n=144) | 0.99 | 0.63 | 1.54 | 0.96 | 1.16 | 0.73 | 1.84 | 0.54 |
| Smoking | Yes (n=72) vs. no (n=328) | 1.38 | 0.84 | 2.26 | 0.21 | 1.34 | 0.78 | 2.32 | 0.29 |
| Age | >29 years (n=179) vs. ≤29 years (n=221) | 1.20 | 0.78 | 1.84 | 0.41 | 0.88 | 0.54 | 1.45 | 0.62 |
| Sex | Male (n=183) vs. female (n=217) | 1.03 | 0.67 | 1.59 | 0.88 | 1.02 | 0.66 | 1.58 | 0.93 |
| Institution | USP (n=194) vs. UNICAMP (n=206) | 1.32 | 0.86 | 2.04 | 0.20 | 1.41 | 0.89 | 2.22 | 0.14 |
| Daily work hours | ≥ 8 hours (n=318) vs. <8 hours (n=81) | 1.94 | 0.97 | 3.88 | 0.06 | 1.69 | 0.84 | 3.37 | 0.14 |
| Exposure years | >2.8 years (n=257) vs. ≤2.8 years (n=142) | 1.96 | 1.25 | 3.07 | <0.01 | 1.85 | 1.09 | 3.15 | 0.02 |
| Jobs (2 vs. 1) | Jobs 2 (n=274) vs. 1 (n=126) | 1.40 | 0.85 | 2.32 | 0.19 | 1.65 | 0.97 | 2.82 | 0.06 |
| Past exposure to laboratory animals | Yes (n=163) vs. no (n=235) | 0.92 | 0.59 | 1.42 | 0.69 | 1.00 | 0.64 | 1.55 | 0.99 |
| Variables | Univariate analysis | Adjusted analysis | |||||||
|---|---|---|---|---|---|---|---|---|---|
| Categories* | RR | 95% CI | p value | RR | 95% CI | p value | |||
| Concentration of dust mite allergen | Continuous | 0.02 | 0.0007 | 0.55 | 0.02 | 0.01 | 0.0005 | 0.29 | <0.01 |
| Concentration of mouse allergen | Continuous | 1.00 | 0.99 | 1.02 | 0.52 | 1.00 | 0.99 | 1.01 | 0.88 |
| Concentration of rat allergen | Continuous | 1.00 | 0.99 | 1.01 | 0.85 | 1.01 | 0.99 | 1.02 | 0.21 |
| Pet ownership | Yes (n=252) vs. no (n=144) | 0.68 | 0.38 | 1.23 | 0.20 | 0.60 | 0.31 | 1.15 | 0.12 |
| Smoking | Yes (n=69) vs. no (n=327) | 1.33 | 0.66 | 2.67 | 0.42 | 1.60 | 0.78 | 3.32 | 0.20 |
| Age | >29 years (n=177) vs. ≤29 years (n=219) | 0.74 | 0.40 | 1.36 | 0.34 | 0.70 | 0.33 | 1.48 | 0.35 |
| Sex | Male (n=181) vs. female (n=215) | 0.80 | 0.44 | 1.46 | 0.47 | 0.71 | 0.37 | 1.37 | 0.31 |
| Institution | USP (n=193) vs. UNICAMP (n=203) | 0.98 | 0.54 | 1.77 | 0.95 | 1.17 | 0.65 | 2.10 | 0.61 |
| Daily work hours | ≥8 hours (n=314) vs. <8 hours (n=81) | 1.01 | 0.49 | 2.11 | 0.97 | 0.95 | 0.44 | 2.02 | 0.89 |
| Exposure years | >2.8 years (n=254) vs. ≤2.8 years (n=141) | 0.83 | 0.46 | 1.50 | 0.53 | 1.02 | 0.54 | 1.93 | 0.95 |
| Jobs (2 vs. 1) | Jobs 2 (n=273) vs. 1 (n=123) | 1.06 | 0.56 | 2.02 | 0.85 | 0.79 | 0.36 | 1.72 | 0.55 |
| Past exposure to laboratory animals | Yes (n=161) vs. no (n=235) | 1.73 | 0.96 | 3.12 | 0.07 | 1.82 | 1.03 | 3.21 | 0.04 |
| Variables | Univariate analysis | Adjusted analysis | |||||||
|---|---|---|---|---|---|---|---|---|---|
| Categories* | RR | 95% CI | p value | RR | 95% CI | p value | |||
| Concentration of dust mite allergen | Continuous | 0.61 | 0.08 | 4.36 | 0.62 | 0.24 | 0.03 | 2.04 | 0.19 |
| Concentration of mouse allergen | Continuous | 1.00 | 0.99 | 1.02 | 0.55 | 1.00 | 0.99 | 1.02 | 0.59 |
| Concentration of rat allergen | Continuous | 1.01 | 1.00 | 1.02 | 0.18 | 1.01 | 1.00 | 1.02 | 0.06 |
| Pet ownership | Yes (n=252) vs. no (n=144) | 0.74 | 0.45 | 1.23 | 0.25 | 0.67 | 0.39 | 1.15 | 0.15 |
| Smoking | Yes (n=69) vs. no (n=327) | 1.10 | 0.58 | 2.09 | 0.76 | 1.21 | 0.60 | 2.43 | 0.59 |
| Age | >29 years (n=177) vs. ≤29 years (n=219) | 0.81 | 0.48 | 1.35 | 0.42 | 0.84 | 0.45 | 1.58 | 0.60 |
| Sex | Male (n=181) vs. female (n=215) | 0.85 | 0.51 | 1.41 | 0.53 | 0.78 | 0.45 | 1.35 | 0.37 |
| Institution | USP (n=193) vs. UNICAMP (n=203) | 1.20 | 0.72 | 1.98 | 0.48 | 1.36 | 0.78 | 2.37 | 0.28 |
| Daily work hours | ≥8 hours (n=314) vs. <8 hours (n=81) | 0.79 | 0.45 | 1.41 | 0.43 | 0.71 | 0.38 | 1.34 | 0.29 |
| Exposure years | >2.8 years (n=254) vs. ≤2.8 years (n=141) | 0.79 | 0.48 | 1.31 | 0.36 | 0.90 | 0.52 | 1.57 | 0.71 |
| Jobs (2 vs. 1) | Jobs 2 (n=273) vs. 1 (n=123) | 0.95 | 0.56 | 1.62 | 0.85 | 0.70 | 0.37 | 1.33 | 0.28 |
| Past exposure to laboratory animals | Yes (n=161) vs. no (n=233) | 1.38 | 0.83 | 2.27 | 0.21 | 1.48 | 0.91 | 2.41 | 0.12 |
ROC analyses were performed to search for a threshold allergen level that could be related to confirmed asthma, asthma symptoms, BHR, and positive skin prick test for mites (Der p1), mice (Mus m1), and rats (Rat n1). The areas under the ROC curves (AUCs) were below significance. The highest AUC value was 66.12 (95% CI: 43.5–88.7), corresponding to analysis of the rat allergen concentration predicting confirmed asthma (Fig. 1).
Receiver operating characteristics (ROC) analysis with estimation of the area under ROC curve (AUC) corresponding to analysis of the rat allergen (Rat n1) concentration in dust predicting asthma confirmed by bronchial challenge test.
In this cross-sectional study, workers were evaluated with regard to a skin prick test, bronchial challenge test with mannitol, and respiratory symptoms, including asthma and rhinitis. One group comprised students and workers exposed to small rodents in laboratories or animal rooms. Subjects in this group were or were not animal handlers, but in both cases, they spent at least part of their time in workplaces that hosted animals at least sometimes. The other group was formed by university workers that had no contact with animals or with workplaces dealing with laboratory animals.
Exposure and long-term duration of exposure were significantly associated with sensitization to occupational allergens, i.e., to a positive skin prick test for at least one of the following allergens: rat, mouse, rabbit, guinea pig, or hamster. More precisely, in the exposed group, 17% of workers had a positive skin prick test for laboratory animals; in the nonexposed group, 3% had a positive skin prick test for these allergens. In addition, past exposure to laboratory animals was associated with asthma in the exposed group. This variable, past exposure, could be seen as a part of duration of exposure. Therefore, it corroborated the association between length of exposure and disease. The levels of allergen in these workplaces were not associated with primary outcomes: sensitization, symptoms, asthma, or BHR.
Asthma, defined by symptoms and a positive bronchial challenge test, showed no increased prevalence as compared with other prevalence studies in this country and region20). The lack of association between exposure and asthma may be consequence of the healthy worker effect, as discussed below. Alternatively, there may really be a lack of association, or there may have been some other interference that did not allow us to detect increased asthma prevalence in the exposed group, for example, subjects' genetics or exposure characteristics.
Number of exposure years was a significant risk factor for occupational sensitization. Subjects who had worked for more than 2.8 years in their jobs showed a higher prevalence of sensitization. However, number of exposure years was not associated with other outcomes, such as asthma, respiratory symptoms, or BHR. This difference is probably related to the fact that sensitization is not perceived by workers, indicating that symptoms, but not sensitization, lead workers to quit their jobs (this is known as the healthy worker effect). Even in prospective cohort studies, the healthy worker effect may be found. For instance, in a follow-up study, 72 participants left the workplace during the study, and on average, those who left had higher mean levels of exposure (1.16 ng/m3) to mouse allergen while enrolled in the study compared with those who stayed (0.55 ng/m3, p=0.06). One subject reported leaving employment because of a mouse allergy21).
In occupational medicine, safety levels of exposure have been an issue. Recent advances in exposure assessment in occupational epidemiology indicate a shift from approaches based on expert judgment to using objective measurements wherever possible. Industry-based studies focused on a small number of facilities are the best able to incorporate measurements because current and historical exposure data are extracted from a restricted number of sources22). For allergic diseases, various authors have attempted to describe safety levels of exposure to animal proteins. We should take into consideration that allergen exposure effects are much more complex than chemical toxic effects. Even so, described threshold levels have been valued in the literature and in public policies for indoor allergens6, 23–27). For instance, in the USA, Germany, and Japan, exposure limits have been described in cornerstone publications28–30).
In this study, the purpose of measurement of occupational allergens was to establish risk levels in the work environment. More precisely, we were interested in the level that induces sensitization. However, in the range of allergen concentrations detected in these workplaces, an association between concentration levels and sensitization was not present. Analysis by ROC curves also failed to detect a cutoff level. The reason for this finding may be oscillations in allergen concentrations.
The Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area, German Research Foundation, has published a list entitled Maximum Concentrations and Biological Tolerance Values at the Workplace (List of MAK and BAT Values)29). The American Conference of Governmental Industrial Hygienists (ACGIH) publishes a yearly guide entitled Threshold Limit Values (TLVs) and Biological Exposure Indices (BEIs)28). These documents describe safe levels of exposure to various chemical and physical agents found in workplaces.
The effects of short-term exposure beyond these limits depend decisively on the mode of action of the substance in question. The occurrence of some exposure peaks (beyond limits) is considered safe if equal or less than 4 times a day, at least one hour apart, with a duration of equal or less than 15 minutes in an 8-hour working day28, 29).
Short-term measurement for 5 minutes or less when the highest exposure concentration is expected may be used as a substitute for measurement of the maximal exposure concentration30). It is generally accepted that short periods of high exposure are possibly more important than the equivalent “dose” accumulation at a lower exposure over a long time31).
In addition to the amount of allergen, the exposure-sensitization relationship may be modified by some other factors, such as parental heredity, viral infections, and concomitant pollutant exposure32). It also has been suggested that the effect of animal allergen is a result of increased levels of endotoxin, which may have dual effects on asthma pathogenesis. Endotoxin exposure may oppose the drive toward Th2-type immune responses and formation of IgE antibodies following allergen exposure. Data have indicated that indoor endotoxin exposure early in life may protect against sensitization by inhibiting Th2-type immune responses33). There is also evidence to support a deleterious effect of endotoxin in relation to asthma. This could be consequence of an airway irritant effect that causes wheezing34). In our sample, endotoxin levels were assessed in dust, and no protective effect was detected. Indeed, endotoxin was associated with wheezing in the last 12 months (data not shown).
One of the relevant consequences of sensitization to a laboratory animal is its association with allergic disease. Workers sensitized to rat allergens had a clear relationship between exposure to rat aeroallergen and allergy-related health end points. These sensitized workers were almost four times more likely to develop chest symptoms compared with non-sensitized subjects5). Portengen et al35) studied the effects of exposure and sensitization in a longitudinal study (median of 2 years follow-up) with 319 workers. According to multiple regression analysis, both sensitization and exposure appeared to contribute independently to decline in lung function in workers exposed for less than four years to laboratory animals (adjusted for age, atopy, sex, and smoking). Lung function decline was most evident in sensitized laboratory animal workers who continued to be exposed to the animals to which they were sensitized. This highlights the implications of sensitization.
In most previously published studies, the diagnosis of asthma was based solely on questionnaires. Use of a mannitol challenge test may be considered an advantage for epidemiological studies. A bronchial challenge test with mannitol is known as an “indirect challenge,” as this agent causes airway narrowing by endogenous release of mediators. Thus, a response to these challenges identifies the presence of airway inflammation and responsive airway smooth muscle, demonstrating an active interaction between the two key features of asthma36). In a study performed in asymptomatic adults with airway hyperresponsiveness to methacholine, mannitol challenge tests were negative in all but one of 16 cases. The authors concluded that mannitol may be more specific than methacholine for asthma diagnosis37).
Limitations of our study may be the use of a cross-sectional design instead of a longitudinal one, which may have hampered confirmation of a possible healthy worker effect; lack of airborne allergen sampling; lack of evaluation of environmental variables, such as room ventilation; and lack of IgE measurement, which could have made evaluations more comprehensive.
Our data indicate that sensitization to laboratory animals may precede allergic symptoms. It has been accepted that the sooner sensitization is detected, the better the patient's prognosis. Therefore, early detection of sensitization is a fundamental step to control allergic symptoms and future asthma risk because exposure may be halted, lowering the worker's risk. Even sensitization has been shown to diminish upon exposure cessation38).
In conclusion, laboratory animal exposure was associated with atopic sensitization. A clear dose-response relationship between allergen levels in the workplace and sensitization was not noticeable. Nevertheless, the long-term duration of exposure (exposure years) was a risk factor for sensitization. Follow-up studies on this sample will bring to light new evidence concerning the association between animal exposure and asthma. Furthermore, these findings might support preventive measures to be taken in these workplaces focusing on routine tasks and exposed individuals.
Conflicts of interest: The authors declare that they have no competing interests.
Acknowledgment: This research was supported by FAPESP and CNPq, Brazil. We are grateful to Mayara Piani Luna da Silva Sicchieri for statistical analysis.
