Module 4: Occupational Asthma - Interblock Exercise

Introduction:

In an ecological research institute in the Netherlands the department of plant ecology investigates the ecophysiology and its relation with geotypes of Plantago species, including P. lanceolata (English plantain), a very common weed that can be found in large numbers in most European countries. Part of the research is performed at the institute with plants of various Plantago species grown in greenhouses. To facilitate measurements of growth parameters, harvesting, genetic crossings, and other manipulations, the plants - which are usually up to maximum 40-50 cm in height - are cultured in pots, and handled during those activities, on tables of standard work height. The department consists of approximately 20-30 staff members, including scientific staff, technicians, PhD students, and maintenance workers for the greenhouses.

Case:

A 23-year old female foreign guest worker (from a North-African country) who worked a few months at the institute, had to work frequently in the greenhouses, measuring and harvesting flowering plantain plants. On one of these days she experienced a severe asthma attack which started during work in the greenhouse with Plantago lanceolata. She had to be brought to the emergency room of a nearby hospital, where she was treated with bronchodilators, upon which her lung function returned to normal. After recovery she was, for further diagnostic purposes, tested by SPT with a common SPT test panel and with a commercially available extract of English plantain, which produced a strongly positive, immediate-type, wheal-and-flare reaction. She also responded positively to several common allergens including house dust mites and grass pollen, and on anamnesis appeared to have a history of moderate to severe asthma since her childhood.

The asthma attack was therefore diagnosed as a typical Type I bronchial response to plantain pollen, due to specific IgE sensitisation. When resuming research work, she avoided during the rest of the project, close contact with plantain plants - necessary manipulations were conducted by colleagues and technical assistants - and she did not experience any further work-related asthmatic symptoms during this period.

The other workers of the department realized that many of them often suffered from more or less severe upper respiratory (URT) and eye symptoms - typically hay fever-like symptoms during work with plantain; several even used to take prophylactic antihistamine medication on such occasions. They considered themselves allergic to plantain pollen, and worried about the risk of also developing work-related asthmatic symptoms, especially an acute asthma attack. The employer contacted an occupational health physician in order to deal with the complaints of the workers.

Two main questions were put forward:

1. Which measures should /could be taken to minimize allergen exposure?
2. Is there indeed a serious risk of further work-related asthma attacks, especially in those suffering from URT and eye symptoms during work with plantain?

The first approach consisted of three steps:

1. A literature search on plantain allergy. Only a few papers in the allergologyl literature appeared to have reported sensitisation to extracts of Plantago pollen in population studies - not in open populations, but in surveys among polyclinical pollinosis patients, particularly in Spain and Italy, with prevalences of Type I sensitisation in these patients of approximately 10-20%. In those studies, practically all Plantago sensitisation was found in patients who also were sensitised to grass pollen, and/or to other weeds like Artemisia or Parietaria. No report of asthma caused by exposure of plantain-sensitised subjects to plantain pollen could be found. Thus, although recognised in several countries as a potential source of allergens, and therefore commercially available as extract for SPT tests, plantain pollen appeared to be very rarely or never included in standard SPT test panels, and to be not commonly considered as an important - i.e. potent and widely occurring allergen.
2. A short questionnaire survey was conducted to specify more precisely the occurrence of work-related and "general" (not specifically work-related) allergy symptoms among the members of the department (n = 25;practially all participated). Of the 25 respondents, 9 did not work with Plantago, and neither in greenhouses where Plantago plants were grown. As expected, none of the 9 "non-exposed" subjects reported work-related symptoms due to working with the Plantago. Of the other "exposed" workers (n = 16), 10 reported "Plantago work related" symptoms: all with URT symptoms, and two of the ten - one being the proband who had experienced the asthma attack - reported also chest symptoms (wheezing and/or chest tightness).
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3. The third step consisted of IgE serology to assess specific Type I sensitisation to Plantago pollen. All participants provided a blood sample, and a specific IgE enzyme immunoassay (EIA) was performed with microtitre plates coated with a commercially available extract of P. lanceolata pollen, and with an extract prepared from P. lanceolata pollen collected at the institute.

Results of the two assays were very similar, with only some small quantitative differences:

• in sera of the 9 "non-exposed" workers, no IgE anti-plantain pollen could be detected;
• sera of the 6 `exposed’ workers who did not report work-related symptoms, were also all negative for IgE anti-plantain pollen.
• 8 of the sera of the 10 exposed workers with work-related symptoms showed a positive serologic IgE anti-plantain pollen reaction: two borderline/weak, 3 moderate, and 3 strong to very strong, with the proband in the latter group, and the other worker reporting chest tightness with a weak/borderline reaction.

To collect data on the prevalence of sensitisation in a control population, and its relation with URT and LRT symptoms, the same IgE anti-Plantago EIA was performed with sera of nearly 282 lab animal workers: 236 who had reported `common’ (ie. not work-related) allergic symptoms, and 46 who had not in a previous cross-sectional study among lab animal workers.

Results: 18 (7.6%) in the first group had detectable IgE to Plantago pollen, and 2 (4.3%) in the second group. Calculation of Odds Ratios revealed that plantain sensitisation was strongly (OR > 10) associated with URT and eye symptoms, while no significant association could be shown with asthmatic symptoms (OR = 1.6; p > 0.05). Similar analyses showed that grass and/or birch pollen sensitisation in this population were associated with rhinoconjunctivitis, but not - after adjustment for sensitisation to mites or pets - with asthmatic symptoms.

Although the risk thus seemed to be low, it was felt that some regular health monitoring should be implemented among the institute’s research workers, to prevent the occurrence of another acute plantain exposure-related asthma attack.