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Prevalence of crab asthma in crab plant workers in Newfoundland and Labrador André Cartier 1, Samuel B. Lehrer 2, Lise Horth-Susin 3,Mark Swanson 4, Barbara Neis 5, Dana Howse 5, Michael Jong 5 1 Hôpital du Sacré-Coeur de Montréal2 Tulane University, New Orleans3 Valley Regional Hospital, Kentville4 Mayo Clinic5 Memorial University ABSTRACT
Objectives. The aim of the study was to determine the prevalence of snow crab sensitisation and occu-
pational asthma. Study design. Prevalence study of symptoms, pulmonary function testing and allergy
testing to crab was conducted in four crab plants of different design in Newfoundland and Labrador, Ca-
nada. Methods. Plants workers in four crab plants were interviewed and offered skin testing, RAST, pul-
monary function testing and peak flow monitoring before and during crab processing. Results. 38%
(n=78) had atopy. 18% (n=39) had certain or highly probable crab asthma. The prevalence of sensiti-
sation in different crab plants varied from 50% (n=19) to 15% (n=16) and the prevalence of certain or
highly probable crab asthma varied from 50% (n=19) to 9% (n=3). Conclusion. Crab asthma and sen-
sitisation to snow crab is a major health problem for snow crab plant workers in Newfoundland and Lab-
rador.
INTRODUCTION
veloping snow crab occupational asthma while This research is conducted in Newfoundland and atopy is associated with an increased risk of sen- Labrador, which is on the eastern seaboard of Ca- sitisation to crab allergens. This research has also nada. In this province, ground fish catch has shown that occupational asthma is primarily dropped 90% from 400,000 metric tonnes in 1988 caused by a process of sensitisation to an allergen to 30,000 metric tonnes in 1993. Snow crab is the in the snow crab that becomes airborne during most commonly processed and the highest reve- processing: snow crab processing is highly aller- nue-producing species, accounting for $1.6 billion genic, as crab allergens are aerosolised in the air during cooking of crab (transported by steam and One of the earliest researches on snow crab oc- water droplets and vapours), butchering of crab cupational asthma that described the condition was conducted in Newfoundland in 1978 (1).
Snow crab asthma is mediated through an al- Since that time, the research related to this prob- lergic mechanism involving the production of lem in the province has been limited and there has specific IgE antibodies to crab meat and cooking been no prevalence study on occupational snow Many workers with crab occupational asthma Research in Quebec in 1984 indicated that the can continue to work using asthma medications.
prevalence of snow crab occupational asthma However, the asthma of some workers will wors- was 15% in plants that have been open for only a few years (1). Smoking increases the risk of de- symptoms in crab plant workers is higher than the ical history of symptoms of asthma during the level of sensitisation. It has been hypothesised season improving after leaving work and posi- that exposure to chemical irritants may explain tive skin test or RAST indicating sensitization to these non-specific symptoms. Various amines, re- snow crab but no peak flow monitoring data.
sponsible for the odour often found in crab plants, Those with a possible diagnosis would have had are released during the cooking of crab (8). These a positive medical history, negative RAST or amines can be toxic at high levels, but their pres- skin test and no peak flow monitoring data, and ence in crab plants probably does not explain those with a diagnosis of unlikely or negative oc- these symptoms, as levels measured in the plants cupational asthma would have had no history of asthma symptoms at work improving after leav-ing work, could have had a negative or positive skin test or RAST and no or negative peak flow In consultation with the Working Group on Shell- fish, comprising plant managers, union represen- Occupational allergy was categorised as high- tatives, Workplace Health and Safety Compensa- ly probable if there were symptoms of rhino- tion Commission (WHSCC) and provincial go- conjunctivitis during the working season and im- vernment officials, four plants with different ages proving after the season, and positive skin test to of the plants, types of processing and ventilation snow crab meat or RAST to snow crab meat or cooking water, regardless of symptoms of occu- In the winter of 2002, current and former pational asthma. It was categorised as possible if workers who volunteered for the study were there were symptoms of rhino-conjunctivitis given questions on their work history, symptoms during the working season and improving after of asthma, rhino-conjunctivitis and rash, cur- the season, symptoms of occupational crab asth- rently, in the past and in the last season. Spirom- ma but negative skin test and RAST to snow etry was conducted and if there was an obstruc- crab. It was classified as unlikely if there were tive pattern this was repeated after ventolin in- symptoms of rhino-conjunctivitis during the halation. Skin tests to common allergens and to working season and improving after the season, snow crab meat were administered to those who but no symptoms for occupational crab asthma agreed. Blood was taken for radio-allergo-sor- and if skin test and RAST were negative. It was bant test (RAST) to snow crab cooking water negative for occupational allergy if there were and meat. Current workers were instructed how no symptoms of rhino-conjunctivitis, occupa- to perform and record peak flows and were in- tional crab asthma, negative skin test and nega- structed to do peak flows every 2 hours every day 2 weeks before working in the crab plantand two weeks during work. Support was given The overall participation rate was 43% (n=215).
The range in participation at different plants into almost certain, highly probable, possible ranged from 38% to 44%. The size of the current and unlikely or negative. Those with a diagnosis work force ranged from 33 to 87 workers. (See of almost certain occupational asthma had symp- toms of asthma during the season, improving af-ter leaving work in their medical history, a posi- The participants’ ages ranged from 17 to 62 tive skin test or RAST indicating allergy to years, with the mean age of 40 years. Fifty-six snow crab and positive peak flow monitoring.
percent of the workers were current smokers, Those with a diagnosis of highly probable occu- 20% ex-smokers and 24% had never smoked.
pational asthma would have had a positive med- Sixty-nine percent were Caucasian, 17% Inuit Table I. Number of participants by plants. All identified former and current
workers in 2001 reached.
and 14% Meti. Fifty-six percent of the partici- oldest crab plant with poor ventilation that pro- cessed cooked crab. The 2nd lowest prevalence Overall, 18% (n=39) of the participants had rate of occupational crab asthma of 10% was in an "almost certain" or "highly probable" diagno- the 2nd oldest but largest plant that has good ven- sis of snow crab occupational asthma and 22% tilation and that cleaned and butchered crabs raw (n=45) a diagnosis of possible snow crab occu- with cooking as the final process before brine pational asthma. In plant 1, ten people (10%) freezing. The lowest prevalence rate of occupa- were given an "almost certain" or "highly prob- tional asthma of 9% was in the newest plant of 2 able" diagnosis. Twenty-seven people (26%) years that cleaned clusters of raw crabs, cooked were given a "possible" diagnosis. In plant 2, and brine froze the crabs without butchering.
nineteen (50%) of participants were given either The prevalence rates of snow crab allergy are si- an "almost certain" or "highly probable" diagno- milar to snow crab asthma. It appears that pro- sis. Five workers (13%) were given a "possible" cessing raw crabs may be associated with a lo- diagnosis of occupational asthma to snow crab.
wer rate of occupational snow crab allergy and In plant 3, seven people (17%) were given either asthma. This will need to be confirmed by furt- an "almost certain" or "highly probable" diagno- her studies to control for other variables inclu- sis of occupational asthma to snow crab. Nine ding the duration of exposure, the efficiency of people (22%) were given a "possible" diagnosis.
In plant 4, three people (9%) were given eitheran "almost certain" or "highly probable" diagno- Acknowledgement
sis of occupational asthma to snow crab. Six Funding was provided by the Canadian Institute people (18%) were given a "possible" diagnosis. The prevalence of occupational allergy was highly likely in 18% (n=39) and possible in REFERENCES
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