Role of health personnel in surveillance program for

occupational asthma

M.Labrecque,M.D.,M.Sc.

Hôpital du Sacré-Cœur de Montréal - April 2006

Objectives

Definition of OA Type of prevention in OA Screening program VS Surveillance program Purposes of a Medical Surveillance program

(MSP) Example of MSP Component of a MSP for OA

Occupational Asthma:Definition

Characterized by variable airflow limitation and/or hyperresponsiveness and/or inflammation due to causes attributable to a particular occupational environment and not to stimuli encountered outside the workplace.

2 types– After a latency period (allergic mechanism)– Without a latency period (Reactive airways dysfunction

syndrome (RADS) exposure to a non specific irritants)

Occupational Asthma (OA)

« Given that OA is one of the most common occupational lung disease, accounting for 10% of all adult-onset asthma and that it is largely preventable, it is clear that the role of prevention deserves emphasis »

Type of prevention

Primary prevention The most effective means of primary

prevention of OA is by control of occupational exposure to respiratory sensitizers by reduction of exposure to the causative substance(s)

Primary prevention;measures

Reducing exposure : (1) substitution of a recognized harmful agent; (2) improved ventilation; (3) automation of process (robotics); (4) enclosure; (5) modification of the process;(6)dust reduction techniques

• Identifying susceptible workers and locating them in aera without exposure

• Administrative controls to reduce the numbers of workers exposed

• Education of school children and workers during the preplacement process regarding risks ( atopics workers and animal exposure)

Secondary prevention

« The major goal for secondary prevention is to detect workers with disease early in its course and ultimately prevent its progression »

Tertiary Prevention

« limiting medical impairment among those with established OA »

Surveillance Program;Definition

Screening VS Surveillance

Often used interchangeably

Screening

The screening is directed toward the individual

Has been defined as «the presumptive identification of unrecognized disease by the application of tests which can be applied rapidly»

Screening aims to detect disease before an individual seeks medical advice,i.e. at a preclinical stage

In OA, the purpose of a MSP is to detect indicators of early sensitization of workers before the progression in permanent asthma

Surveillance; Definition

Surveillance is directed toward the population from which the individual comes (has a public health focus )

The detection of «an index case in a workplace may trigger public health action in the form of an industrial hygiene investigation of the workplace implicated»

Surveillance; Definition

Surveillance is defined «continued watchfulness over the distribution and trends of disease through the systematic collection, consolidation and evaluation of morbidity,mortality, etc. and even more important, the timely distribution of data

Rational for Medical Surveillance

In Ontario Province and United Kingdom inclusion of provision for surveillance in regulations has been instituted without reference to their rationale or effectiveness

(no direct evidence that groups undergoing medical surveillance have better outcomes)

But the main rationale for MS is the «indirect» evidence that once OA has developed in a worker, the

outcome is best with (1) early diagnosis (2 )early removal from exposure to the agent (3) and milder asthma at the time of removal

Medical Surveillance Program (MSP);purposes

« Evaluate periodically the health status of the entire workforce in relation to work environment with the following objectives»

(1) recognize changes in health before clinically important adverse health outcomes

(2) identify potentially hazardous working conditions using grouped health and environmental information

(3)Evaluate the effectiveness of exposure controls through the ongoing collection and analysis of the relevant data

(1) Recognize changes in health before clinically important adverse health outcomes

Example : medical surveillance program for workers in the detergent enzyme industry

The MSP includes Periodic questionnaires Skin-prick test with a dilution solution of the enzyme Spirometry

Every 6 months for 2 years then yearly

Example: Detergent enzyme industry

As other HMW occupation allergens,upper respiratory allergic symptoms often precede the onset of allergic asthma

Workers who developed symptoms and had positive skin test to the enzyme were moved away from further exposure and rate in OA in this setting significantly decline

Ref: Schweigert MK. Clin Exp Allergy 2000; 30(11);1511-1518

Example : Complex platinum salts

A positive SPT to Complex platinum salts

is highly predictive to the development of later OA ( 100%)

• A MSP who remove those found with SPT positive has been reported to be very effective

Ref: Merget R. J Allergy Clin Immunol 2001; 107(4):707-712

(2) Identify potentially hazardous working conditions using grouped health and environmental information

Example: for isocyanate exposed workers

In the case of LMW sensitizers,only a minority have serum IGE antibodies to diisocyanates, SPT cannot be done neither, therefore MSP to isocyanates have relied on symptom questionnaire and spirometry

Example; isocyanate

– PPI program in Quebec Province– Target 4,000 spray-painter in the car industry

– The MSP :• Groupe information session• Auto-questionnaire at the end

PROSPECTIVE EVALUATION OF THE PROGRAMONGOING

Which component of the program may be responsible ?

Questionnaire? How Valid Are Questionnaire/Symptoms? They are relatively sensitive but not specific (performed better in excluding than confirming the presence of OA) emphasing the need for objective confirmation

Ref 1 : Malo JL.Am Rev Respir Dis 1991;143:528-532

Which component of the program may be responsible?

Spirometry? In one study done in polyurethane foam-making company showed a high proportion of false positive responses among subjects who had apparent spirometric changes in the absence of symptoms on questionnaire (and spiro did not add benefit to the questionnaire)

Ref 2: Kraw M. Am J Ind Med 1999; 35(1);87-91

Which component of the program may be responsible?

Test of Nonspecific Bronchial Hyperesponsiveness (methacholine inhalation test) impracticable for screening an entire

worker populations owing to the non specificity of the test and no convincing evidence that pre-employment testing can predict development of OA

However,in workers in whom the pretest probability of OA is high (i.e. positve SPT and history) methacholine is very useful

If a symtomatic worker is unresponsive to methacholine while still exposed at work, asthma and OA can be excluded with a high degree of certainty

Ref: Tarlo SM. Canadian Thoracic Society guidelines for Occupational Asthma Can Respir J 1998;5(4);289-300

Which component of the program may be responsible ?

Immunological tests : When appropriate, detection of specifc IGE by serological immunoassay or skin testing with occupational allergens may serve as useful screening

Relevant for HMW (enzymes,latex,psyllium) Exception LMW; platinum salts

Conclusion

Should medical Surveillance be Conducted?

• There is evidence from Ontario Canada based

on nonrandomized studies that OA has been diagnosed earlier, with better outcome in thoses exposed to an asthmagen for which medical surveillance was provided

Ref :Tarlo SM. Occup environ Med 2002;59 (1):58-62