Cases of occupational asthma assessed at the National Institute for Occupational Health - Occupational Medicine Clinic from 1997-2007

Abstract

Background Occupational asthma is one of the most commonly reported occupational respiratory diseases in industrialized countries. Literature suggests that about 15% of all adult-onset asthma is caused by workplace exposures. It is potentially preventable and the prognosis is good with early diagnosis and adequate treatment. However, occupational asthma is under-diagnosed and under-reported. Identification of common causative agents and employment of preventative measures are necessary for proper management and control. Objectives 1. To characterize occupational asthma cases assessed at NIOH Occupational Medicine Clinic from 1st January 1997 to 31st December 2007 in terms of: • types of industries, occupations and agents • duration of exposure prior to onset of occupational asthma • time from onset of symptoms to diagnosis • nature of exposure e.g. intermittent, daily, etc. 2. To investigate factors influencing latency period in cases of sensitizer-induced asthma 3. To investigate factors influencing lag time to diagnosis in cases of sensitizer-induced asthma Methods A record review of a series of cases of occupational asthma was done. All cases of occupational asthma diagnosed from 1st January 1997 to 31st December 2007 by NIOH doctors were identified from the Clinic’s electronic database. All the records of patients who had a final diagnosis of occupational asthma were assessed using a standard data capture sheet. Doubtful cases were presented at the NIOH Occupational Medicine clinical discussion meeting for a consensus decision as to whether they qualified to be included in the study or not. Ethical approval was granted by the University of the Witwatersrand Human Research Ethics Committee (Medical). vi Results One hundred and forty two cases of occupational asthma were identified. Of these, 131 were sensitizer-induced and 11 were irritant-induced asthma. Low molecular-weight agents were in the majority with isocyanates, welding fumes, vanadium being the most common. Within the high molecular weight category, wheat was the most common. The majority of cases emanated from the Engineering, Chemical, Smelter and Food industries. Latency period from first exposure to development of symptoms was surprisingly long: a mean of 9.8 years and a median of seven years. The time from onset of symptoms to diagnosis was also long (mean of 4.9 years and median of three years). Younger cases had a shorter latency period and a longer delay in diagnosis. Agents and jobs for irritant-induced asthma cases varied widely and some came from unexpected industries. Discussion This review of asthma referrals to the NIOH Occupational Medicine Clinic has highlighted causative industries and identified exposure agents implicated in cases of occupational asthma. The very wide range of industries, occupations and agents associated with these cases is suggestive of a wide-spread occupational asthma problem in the region referring cases to the Clinic. The long latency period and delay in diagnosis are of concern since prompt diagnosis and removal from exposure is associated with a better prognosis. Irritant-induced asthma is infrequently reported in the local literature, but the range of agents and jobs is possibly indicative of under-diagnosis. Conclusion Occupational asthma is potentially preventable. New cases still arise particularly in poorly controlled workplaces which are capable of employing basic measures to control exposures. Medical surveillance, prompt diagnosis, proper medical management and application of workplace preventative measures are essential in decreasing the burden of disease and impairment