Overview
Occupational infections can be easy to miss unless there is a high index of suspicion
A detailed occupational history combined with knowledge of infectious diseases will often reveal the diagnosis of unusual illnesses due to infectious hazards
There are no anatomical or pathological differences between infectious diseases arising from work exposures and those arising from non-work exposures
Immunization, universal precautions, personal hygiene measures, education and personal protective equipment where appropriate are the main strategies for prevention
Prevention of infection is an important aspect of occupational health practice as it will impact favourably on communicable disease in the general population
Introduction
The pattern of infectious hazards at work has changed over time, and specific occupational infections, while not common, can be serious and easy to miss unless there is a high index of suspicion combined with an understanding of infectious diseases (Box 12.1). Furthermore, infections of predominantly historic interest in the developed world continue to be a significant problem in the developing world, and the changing pattern of travel means that those who visit or work overseas remain exposed (see Chapter 19). Drug resistance, the resurgence of certain diseases and the emergence of new or previously unrecognized organisms further complicate matters, as does the increasing number of immunocompromised individuals. A detailed occupational history is therefore essential, as this will often reveal the diagnosis of unusual illnesses due to infectious hazards.
- an external agent—the organism that produces the infection
- a susceptible host—attributes that influence an individual’s susceptibility or response to the agent e.g. age, sex, lifestyle
- environmental factors which bring the host and agent together—factors that affect the agent and opportunity for exposure e.g. climate, physical surroundings, occupation, crowding.
An infectious disease is endemic if there is a persistent low to moderate level of occurrence. It is sporadic if the pattern of occurrence is irregular with occasional cases, and when the level of disease rises above the expected level for a period of time, it is referred to as an epidemic. An outbreak is two or more cases of illness which are considered to be linked in time and place. A pandemic is the worldwide spread of a new disease.
Occupational infections may be work specific or may be common in the general population, but they occur more frequently in those with occupational exposure. There are no anatomical or pathological differences between infectious diseases arising from work exposures and those arising from non-work exposures. However, if an infection is unusual in the general community and known to be a risk factor in a particular occupation, the connection between infection and work can usually be established reasonably easily. Like all occupational diseases, they are mostly preventable (Box 12.2).
There are several work-related factors that can predispose a worker to contracting an infection. These include:
- intentionally working with micro-organisms, e.g. laboratory workers
- having contact with people who have an increased prevalence of infectious disease, e.g. healthcare workers
- having contact with animals that may be reservoirs for infectious diseases, e.g. agricultural workers
- working in an area where an infectious disease is endemic, e.g. business travellers/expatriates
- having an increased likelihood of a micro-organism gaining entry into the body, e.g. through cuts, sharps injuries or dermatitis.
There are three main categories of occupational infections (Figure 12.1):
- zoonoses
- infections from human sources
- infections from environmental sources.
- details of the hazard group the agent belongs to
- the diseases it may cause
- how the agent is transmitted
- the likelihood of exposure and consequent disease (including the identification of those who may be particularly susceptible e.g. asplenics, those with immune deficiencies, pregnant staff), taking into account the epidemiology of the infection within the workplace
- whether exposure to the hazard can be prevented
- control measures which may be necessary
- monitoring procedures
- need for health surveillance, which may include assessment of worker’s immunity pre and post immunization
Hazard Classification
- Group 1—unlikely to cause human disease, e.g. Bacillus subtilis
- Group 2—can cause human disease and may be a hazard to employees; it is unlikely to spread to the community, and there is usually effective prophylaxis or treatment available, e.g. Borrelia burgdorferi
- Group 3—can cause severe human disease and may be a serious hazard to employees; it may spread to the community, but there is usually effective prophylaxis or treatment available, e.g. Bacillus anthracis
- Group 4—causes severe human disease and is a serious hazard to employees; it is likely to spread to the community and there is usually no effective prophylaxis or treatment available, e.g. Ebola virus
When a biological agent does not have an approved classification the COSHH regulations contain guidance on how biological agents should be classified. The classification should be based on the best available evidence and a precautionary approach may be necessary especially when an agent is newly discovered or emerging.
Figure 12.1 Main occupational groups at risk of infections. (a) Zoonotic infections: Farmers and other agricultural workers, Veterinary surgeons, Poultry workers, Butchers and fishmongers, Abattoir workers and slaughtermen, Forestry workers, Researchers and laboratory workers, Sewage workers, Tanners, Military staff, Overseas workers. (b) Infections from human sources: Healthcare workers, Social care workers, Sewage workers, Laboratory workers, Overseas workers, Archaeologists (during exhumations). (c) Infections from environmental sources: Examples include legionellosis and tetanus, Construction workers, Archaeologists, Engineering workers, Military staff, Overseas workers.
Epidemiology
No single source of information provides comprehensive data on occupationally acquired infections, and data sources underestimate the true incidence. In the UK, information is collated from a variety of sources including statutory reporting schemes such as the Public Health (Control of Diseases) Act 1984 (as amended by the Health and Social Care Act 2008), the Reporting of Disease and Dangerous Occurrences Regulations (RIDDOR) 1995, and Social Security Industrial Injury (Prescribed Diseases) Regulations 1985, and voluntary schemes such as the Labour Force Survey, and The Health and Occupation Reporting (THOR) network.
The relatively short incubation period (commonly days or weeks) between exposure and onset of disease for most infectious diseases means that the relationship of an infection to work is usually obvious. However, identifying this relationship can be a problem for infectious diseases with longer latencies such as hepatitis C, where the diagnosis may be made several years after exposure and where exposure can occur in occupational and non-occupational circumstances.
Data from UK reporting schemes indicate that the industries with the highest estimated rates of work-related infection are Health and Social Care, Fishing and Agriculture and Forestry. Diarrhoeal illnesses are the most frequently reported work-related infections.
Zoonoses
These are infections that are naturally transmissible from vertebrate animals to man. Transmission may occur by direct contact with an animal (e.g. orf), through a contaminated environment (e.g. leptospirosis) and via food (e.g. campylobacteriosis), or indirectly via vectors, such as mosquitoes or ticks (e.g. West Nile fever and Lyme disease).
There are approximately 40 zoonoses in the UK and approximately 300 000 people in a variety of occupations are potentially exposed. Their diagnosis, surveillance, prevention and control require close collaboration between a variety of agencies and disciplines particularly between health and agriculture (Box 12.3, Box 12.4).
Control of the disease in the animal reservoir
- Stock certification and immunization (e.g. anthrax or brucellosis)
- Quarantine measures (e.g. for psittacine birds)
- Infection free feeds (e.g. Salmonella-free feed for poultry)
- Avoidance of contamination of animal drinking water
- Test and slaughter policies (e.g. for bovine tuberculosis)
- Good standards of hygiene in stock housing
- Regular stock health checks by vets
- Meat inspection
Safe work practices
- Safe handling of animals or animal products (for all zoonotic infections)
- Safe disposal of carcasses and animal waste (e.g. hydatid disease)
- Avoidance of equipment likely to cause cuts, abrasions, and grazes
Strict personal hygiene
- Covering existing wounds with waterproof dressings before work
- Prompt cleaning of any cuts or grazes that occur while handling animals
- Regular and correct hand washing and avoidance of contact between unwashed hands and the mouth, eyes, or face
Personal protective equipment
- Waterproof aprons or parturition gowns
- Obstetric gauntlets for lambing/calving
- Face protection if there is a risk of splashes from urine or placental fluids
- Plastic or synthetic rubber gloves for oral or rectal examinations
- Gloves, overalls and face protection for slaughtering animals or dressing carcasses
- Chainmail gloves for butchers
Other measures
- Immunization of at-risk workers—anthrax, Q fever
- Provision of health warning cards—leptospirosis
NB: for protection of laboratory worker advice on control measures has been provided by the Advisory Group on Dangerous Pathogens
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