Occupational asthma cases assessed at the National Institute for Occupational Health Referral Clinic from 1997 to 2007

Introduction
Occupational asthma is the most commonly reported occupational respiratory disease in industrialized countries and it is approaching pneumoconiosis in developing countries. South Africa does not have a surveillance scheme or register for recording occupational diseases; as such the incidence and prevalence of occupational asthma in South Africa is not known. A few studies done in different workplaces have reported estimated prevalences and incidences although comparison among them is difficult because of different definitions of asthma and diagnostic methods. Information from cases assessed at the NIOH’s referral clinic provides an opportunity to describe characteristics of those cases that come from a wide variety of industries within the NIOH region, making targeted prevention possible.

Methods
A record review of all 142 occupational asthma cases diagnosed from January 1997 to December 2007 at the National Institute for Occupational Health’s Clinic was done to characterize the cases in terms of causative agents, industries, latency period, smoking and time to diagnosis. Data were analysed using STATA.

Results
The majority (92,2%) was as a result of exposure to sensitisers, while the remaining cases, 7,8%, were due to irritant exposure. Isocyanates and welding fumes were most common among low molecular weight agents, with wheat the commonest among high molecular weight agents. Key exposure industries were engineering and chemical. Diagnostic lag and latency periods were long among young employees. Agents and jobs for irritant-induced asthma cases varied widely and some came from unexpected industries.

Discussion
The wide range of industries, occupations and agents is suggestive of a wide-spread occupational asthma problem in the region referring to the Clinic. The long latency period and delay in diagnosis indicate a need for in-depth look at systems for controlling exposures and surveillance. The findings can educate practitioners, employers, and employees about local risks and provide basis for a surveillance system.