EXECUTIVE SERIES Occupational Asthma for the GP By Dr Tan Keng Leong This article is part of a series on workplace safety and health for healthcare institutions. A 41-year-old who had been a carpenter for more than 20 years, presented with rhinitis, chest tightness and cough after exposure to chengal wood dust for one year. He had previously worked with different woods without any health problems. He was well during his month-long vacation when he was back in his home country. His symptoms recurred upon his return to work with chengal wood dust exposure. Serial peak flow monitoring showed significant drop in peak flows during workplace exposure to chengal wood dust. Specific inhalational challenge test resulted in an isolated immediate asthmatic reaction, thus confirming the first reported case of occupational asthma due to chengal wood dust.1 Key points even after removal from Sensitiser-induced asthma 1. Occupational asthma is now exposure. This is characterised by a variable the most common occupational 5. Identification of the specific time (latency period) during which respiratory disease in Singapore. causative agent and early removal “sensitisation” to a specific agent 2. It is a legally notifiable from exposure can prevent the present in the worksite takes place. occupational disease under the risk of a severe or fatal asthmatic The patient does not experience Workplace Safety and Health attack in the workplace. any respiratory problems during the (WSH) Act and a compensable latency period of weeks to years. occupational disease under the Definition Once sensitisation has occurred, the Work Injury Compensation Act. Occupational asthma is defined worker may be affected by very low 3. Appropriate management and as asthma due to conditions concentrations of the offending agent. prevention is important because attributable to work exposures and of the medical, socio-economic not to causes outside the workplace. Irritant-induced asthma and legal consequences. This occurs without a latent period 4. Continued exposure to the Types after substantial exposure to an causative agent may lead to The two types of occupational irritating dust, mist, vapour or fume permanent airway damage, asthma are distinguished by whether (such as chlorine, sulphur dioxide or resulting in persistent asthma they appear after a latency period: acid fumes). Reactive airways dysfunction 12 • SMA News May 2015 syndrome is a term used by some to Table 1: Common causes of occupational asthma and occupations at describe irritant-induced asthma caused risk by short-term, high-intensity exposure Causative agents Occupations (eg, an accidental spill or other high level Isocyanates (eg, toluene diisocyanate ) • Polyurethane foam workers respiratory irritant exposures). • Spray painters and varnishers • Insulation workers Prevalence Acid anhydrides (eg, phthallic • Chemical workers making or using Recent estimates suggest that 9% anhydride) polyester, epoxy, alkyl resins to 15% of adult asthmatics may have • Spray painters occupational asthma.2 In Singapore, Pharmaceuticals (eg, antibiotics, • Pharmaceutical technicians although the disease is common, it glutaraldehyde) • Health care workers is likely to be under-diagnosed and • Veterinary workers under-reported. • Animal feed workers Causative agents and occupations Soldering flux, colophony • Soldering operators at risk Welding fumes • Welders Substances that cause occupational Wood dust • Carpenters asthma are classified either as high Metals and their salts (eg, nickel, • Electroplaters molecular weight or low molecular cobalt, chromium) • Welders weight allergens. High molecular • Machinists weight allergens include: products Foodstuffs (eg, grain, soybean, flour) • Food processing workers of animal, plant or microbial origin Enzymes (eg, Bacillus subtilis) • Bakers such as laboratory animal allergens, • Detergent workers fish and seafood proteins, flour and • Pharmaceutical workers detergent enzymes. Low molecular weight allergens include: chemicals Animal products (eg, dander, excreta, • Farmers and metallic agents such as acid urine) • Zookeepers anhydrides, antibiotics, isocyanates, • Laboratory technicians western red cedar, amines, colophony and metals. helpful. An SDS is a document that airflow obstruction. Symptoms include In Singapore, the most common contains information on the potential episodic breathlessness, wheezing, causative agents reported were hazards (health, fire, reactivity and coughing or chest tightness, commonly isocyanates (31%), colophony environmental) and how to work in response to certain trigger factors. fluxes and solders (13%), welding safely with the chemical product. WSH A childhood history of asthma fumes (9%) and wood dust (4%).3 Regulations require the employer to does not exclude the diagnosis of Isocyanates are the leading cause make the SDSs available to workers occupational asthma, as these patients of occupational asthma in a number who may potentially be exposed may also become sensitised to a of other industrialised countries.4 to hazardous substances at the specific agent in the workplace. Some common causative agents workplace. Work-relatedness may be of occupational asthma and the suggested based on: the history of occupations at risk are summarised in Diagnosis improvement when away from work Table 1. The diagnosis is made by: (eg, annual or maternity leave), and onset of symptoms during working Diagnostic approach 1. Establishing the presence of periods. Take a detailed medical and asthma; occupational history to assess current 2. Demonstrating relationship Diagnostic pitfalls and previous job exposure to causative between asthma symptoms and Bronchial asthma agents such as chemicals, proteins, work; and Occupational asthma may also organic dusts and animal products. 3. Establishing exposure to a specific present as chronic cough (eg, without Knowledge of common causative causative agent. episodic breathlessness or wheezing). agents and their associations with Repeated absence from work due to various occupations and industries, A clinical diagnosis of asthma is frequent “bronchitis” is another typical and information obtained from made based on appropriate clinical presentation and should trigger the safety data sheet (SDSs) are often history and evidence of reversible suspicion of occupational asthma. May 2015 SMA News • 13 Relationship to work Serial peak expiratory flow rate exposure at various locations in the In occupational asthma, there Clinical history alone is generally plant. This is useful in establishing a is a temporal relationship between not sufficient to make a definitive non-exposed work area where the the asthma symptoms and exposure diagnosis of occupational asthma. patient could be transferred to. In at work. For instance, the patient Serial peak expiratory flow rate addition, high risk areas requiring may report that asthma occurs during periods at work and away further control measures can be soon after entering the workplace from work is a useful tool for the identified. or when performing specific tasks. objective documentation of work- The patient may not necessarily relatedness. Management be aware that the symptoms are For all workers confirmed to have temporally related to work as the Specific bronchial provocation occupational asthma, permanent asthma symptoms are commonly test (specific inhalation transfer to a job with absolutely no more pronounced in the evening, challenge test) exposure to the causative agent is at night, or in the early morning (ie, A positive specific inhalation recommended as further exposure outside the workplace). Symptoms challenge test to the causative agent may trigger a severe or even fatal (eg, wheezing) may be triggered by is considered the gold standard asthma attack. inhaled irritants, such as cigarette for the diagnosis of occupational The patient should be counselled smoke, engine exhaust, strong asthma. A workplace challenge may with regard to the disease, role of odours, cold, exercise, which also sometimes be performed when it is medications (preventers and relievers), frequently occur outside the not possible to perform controlled inhaler technique, avoidance of trigger workplace (eg, in pubs or during specific challenges in the laboratory. factors and treatment compliance. exercise). Therefore, a major pitfall in the clinical diagnosis of occupational Environmental monitoring Pharmacological treatment asthma is that the patient with Environmental monitoring is Pharmacological treatment occupational asthma may have few useful in documenting exposure is similar as for any patient with symptoms during work and most to the specific agent. It is also asthma. Short-acting inhaled beta2- symptoms outside the workplace. useful in the assessment of risk and agonists, taken as needed, are used Occupational asthma often effectiveness of industrial hygiene in the treatment of acute asthma responds well to appropriate medical control measures based on the level symptoms and exacerbations treatment, at least initially. This may of exposure. Personal air sampling and in the prevention of exercise- lead to the missed or late diagnosis of workers using portable collection induced bronchospasm. Persistent of occupational asthma. devices at various workstations and asthma is controlled with daily different breathing zones may be anti-inflammatory therapy Hypersensitivity pneumonitis performed to study the pattern of (preventer medication, ie, inhaled Hypersensitivity pneumonitis glucocorticosteroids).