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);

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):

(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 PROGRAM ONGOING

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:

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);

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