Introduction to Occupational Health Hazards

New Frontiers in Occupational Disease

Farhana Zahir*

Prism Educational Society, Aligarh, U.P., India

Abstract

If a disease demonstrates frequency in a group of people of a particular occupation more than the one that takes place in general public and has a demonstrable record between a particular illness and specific work/work-related environment, it is classified as an occupational disease. The development of a new class of occupational disorders is by-product of the recent uncontrolled man-man, man-machine and man-agents’ interaction. A small percentage of workers amongst the total working population of the world have access to occupational health related services, the access gets diminished if the worker is a child labour from a developing country. Moreover, the constant evolution of newer work areas and substances has led to continuous revision of list of causative agents and occupational health hazards by various agencies. Diving medicine is one such emerging branch of medicine dealing with specific health aspects of deep sea divers. The study of cause-effect relationship of occupational diseases will contribute towards reducing cases of work related disorders. Biological agents become causative agents through generation of bio aerosols or as routine infectious agents affecting biomedical scientists, laboratory technicians, medical and paramedical staff. The duration of exposure and varying doses (low-high) of hazardous chemical complexes are a source of a range of disorders from long term effects like neuro- behavioural dysfunction to immediate effects like burns. Some substances sensitise both airways and skin leading to respiratory and skin disorders. Similarly, the intensity and duration of exposure to the physical agents lead to an array of disorders ranging from white finger vibration, trench foot, barotrauma upto cancer. Besides exposure to biological, chemical, physical, ergonomic disease causing agents a worker is also prone to altered psychosocial agents at workplace. Violence and accidents occur at workplace. Discrimination (gender/ethnic/ migrant status), disturbed circadian rhythm, work pressure, lack of job satisfaction and social life leading to depression and anxiety have become a new normal in working class.

Keywords: Bacteria, Bradford Hill’s Criteria, Compressed or decompressed air, Universal diagnostic criteria, Ergonomic agent, Extremes of temperature, Fungi, International Labour Organization, Needle-stick injury, Noise, Occupational diseases, Organic Dust, Parasites, Protein, Psychosocial agent, Radiation, Respiratory disorders, Skin disorders, Sa substances (Substances causing, airway sensitisation), Vibration, Virus, WHO, work-related Musculoskeletal Disorders (WRMSDs), Virus.

* Corresponding author Farhana Zahir: Prism Educational Society, Aligarh, U.P., India; Tel: +91 9760986931; +91 798386098; Email: [email protected]

INTRODUCTION

The first incidence of work-related disorder was identified in 1775 in ‘Chimney sweep boys’. Half of the worlds’ population is worker. Occupational disorders have become widespread as a by-product of industrialization and globalization. As per the statistics given by International Labour Organization (ILO) in a single year (2000), 2 million people died, around 271 million people were injured and about 160 million people became ill as a result of occupation-related health hazards. The risk of occupational diseases increases many folds in case of accidents like Bhopal methyl isocyanide leakage or the recent japanese tsunami which led to thermal reactors’ meltdown.

In early days, only industry workers or mine workers especially those working in coal mines were considered to be exposed to health hazards owing to their occupation. But now-a- days, modern concept of health has widened the scope of Occupational disorders by including all types of service trades, agriculture, health care sector and ergonomics. Newer occupations like those of biomedical scientists (e.g., conducting research on deadly Ebola/Marburg virus/Zika Virus) or medical laboratory technicians (e.g., performing diagnostic test of TB) create previously unrecognized occupational disorders. Unconventional health risks which come under occupational hazard are extreme climatic conditions (e.g., armed forces working on high altitude/scientists working in Antarctica), long hours use of computer, Vibrations (e.g., Transport vehicle) etc. Work-related stress due to lack of sleep, mental trauma etc. and violence as faced by medical staff are all other recognized occupational hazards. The magnitude of increment in cases of work-related diseases pressurises International Labour Organization to add new substances/sources to their list after every few years. Any disease contracted as a result of exposure to risk factors arising from work activity is termed Occupational Disease according to Occupational Safety and Health Convention, protocol 2002. For any disease to qualify as occupational disease it must demonstrate disease frequency more than general public and have a demonstrable record between a particular illness and specific work/work-related environment.

In accordance with World Health Organization reports, only 15% global workforce has access to Occupational health-related services. This becomes more complicated when 70% of world’s working population live in developing countries. Further, the fact that people most vulnerable to work-related disorders come from the weakest sections of the society makes the issue more complicated. As per the statics issued by International Labour Organization, children between the age group 5-17 comprise 352 million work force, of which 170 million work in perilous settings despite serious intervention of 130 countries making stringent child labour laws. The physical, moral and mental fabric of child workers undergoes irreversible loss when they work in dangerous situations without proper access to basic health amenities. Many child workers acquire illness which last a lifetime.

Occupational diseases are avoidable, if proper care is taken. Therefore, it becomes imperative to study cause-effect relationship; though, complexities of human behaviour also play a role, for instance, willingness of a worker to adapt to strict hygiene/wear a helmet or take other safety precautions. The manner in which human body interacts within a certain work environment determines its stress level. But the previous work history of the person is also a determining factor while studying his susceptibility towards disease. Body-burden of slow metabolizing substances (like chromium or lead or benzene), physical distortion (like Carpel Tunnel syndrome) acquired at an earlier work will certainly influence his chances of acquiring a malady. Gene pool, age, gender, health, race, lifestyle are other aspects which will undoubtedly manipulate one’s likelihood of acquiring a disease. The source of information for such analysis primarily comes from epidemiological and scientific studies. Industrial accidents like Chernobyl also contribute vast amount of data.

There are three kinds of Interactions (Fig. 1) a person is supposed to experience during his/her workings years. They are man-man (biological interaction), man-machine (physical interaction), man-work agents (chemical interaction).

Fig. (1))

The web of interactions.

Man-Man Interactions (Biological Interaction)

The interaction between workers and management or amongst the workers must remain smooth under ideal conditions. Man-man interactions, whenever get adverse at work place, may lead to anxiety and depression which in turn, may be a cause of violence/harassment/abuse or in extreme cases may take the magnitude of murder or suicide or even both.

Man-Machine Interaction (Physical Interaction)

The interaction of a man with tools or introduction of new tools or machines is very important. For instance, introduction of computers in every field like, designing, education, transport, construction, and diagnostics in the last few decades has a huge impact on workforce and work ethics. It also depends on age and skill level of the worker. The user-friendly design of the machine is important besides the ergonomic design of the visual display unit at workplace. Man-machine interactions in their subtlest form may lead to mild emotional strain or musculoskeletal disorder while in extreme cases any fault in the machinery/ improper use of the equipment/lack of safety measures/human error may result in ghastly accidents leading to lifelong disability or death in worst cases.

Man-Work Agents Interaction (Chemical Interaction)

The interaction of workers with agents of work like use of toxic chemicals (Chemical agent) or handling infectious materials (Biological agents) or extremes of temperature or constant vibrations (Physical agents) may lead to compromised health of the worker or may lead to permanent disability or may even prove to be fatal.

Universal Diagnostic Criteria for Identification of Occupational Diseases

The duration of exposure, uniformity and specificity serve as universal diagnostic criteria (Fig. 2) for identification of occupational disease. In order to qualify as occupational disease besides duration of exposure, uniformity and specificity, preliminary interventional studies must support the occupational disease.

Duration of Exposure

The longer the duration of exposure the greater the impact, hence, stronger is the likelihood for the development of the disease.

Uniformity

There should be coherence in results/reports from various laboratories regarding the disease. All epidemiological and animal studies must demonstrate cause and effect relationship.

Specificity

Exposure to a definite risk factor results in a noticeably defined pattern of ailment.

Interventional Studies

A primary preventive trial may suggest removal of a specific risk factor or hazard from a particular work environment to remove incidence of a specific disease.

Fig. (2))

Universal Diagnostic Criteria.

Bradford Hill’s Criteria

In 1965, Sir Austin Bradford Hill proposed a criteria using cause-effect in identification of disease. It is widely used by epidemiologists even today after 53 years since it was first published; despite a lot of debate over its absoluteness. The nine point criteria, famously known as Hill’s Criteria include Strength, Consistency, Specificity, Temporality, Biological gradient, Plausibility, Coherence, Experiment and Analogy for identification of disease. It was using this approach he demonstrated the relationship between cigarette smoking and lung cancer. As occupational diseases are studied in a live setting there is an intrinsic chance of error which must be eliminated during statistical analysis before making final conclusion while using Hill’s Criteria. The anticipated types of errors are random, systematic and logical.

Broad Classification of Occupational Diseases

The Occupational diseases can be broadly classified according to disease causing agents. Thus, there are following six classes of diseases (Fig.3).

Fig. (3))

Broad Classification of Occupational Diseases.

Disease caused by Biological agent.

Disease caused by Chemical agent.

Disease caused by Physical agent.

Disease caused by Ergonomic agent.

Disease caused by Psychosocial agent.

Disease caused by Accidents.

Occupational Diseases caused by Biological Agent

Bacteria, Fungi, Viruses, Parasites and Proteins can act as disease causing biological agents (Fig. 4). There are two ways by which biological agents act as occupational hazard. The first way is generation of bio aerosols and second is as the routine infectious agent. Any particulate matter of organic origin is defined as bioaerosol [1]. Pollen grains, bedding material, manure, molds, high molecular polymers released by bacteria and fungi (termed endotoxin or beta glucans, respectively), low molecular polymers released by fungi called mycotoxins, volatile organic compounds etc. may form bioaerosol. Biological agents of disease are elaborately discussed in chapters 3, 4 & 5.

Fig. (4))

Broad classification of Occupational Diseases caused by Biological agents.

Bacterial Infections

Methicillin-resistant Staphylococcus aureus (MRSA) is a bacterial strain reported in hospital settings since 1960.It causes a spectrum of diseases related to soft tissue and skin rashes, abscesses etc. As Staphylococcus aureus is a drug resistant bacterium, it is a threat to hospital staff like doctors, nurses and students [2]. Work-related Sarcoidosis is a multiorgan granulomatous disease with presumably mouldy or mycobacterium indoor office or nano particle exposure as has emerged from World Trade Centre office respondents [3]. Legionellosis is a pneumonia like infection is caused due to a bacterium (L. pneumophilaI) by exposure to aerosol generated by water. Workers of telephone manholes [4], glass processing industry [5] and non-industrial working environment [6] like wastewater treatment plants, cooling towers, and humidifiers are well known as the patients for disease. Multi drug resistant gram negative enteric pathogens (GNEP) have also recently emerged as a problem to animal husbandry. Nosocomial Infections or hospital acquired infections are discussed in detail in chapter 4. But development of Carbapenem-resistant Enterobacteriacae like New Delhi metallo-β-lactamase (NDM-1) has become a major cause of public health concern worldwide due to the development of drug resistant mutants.

Ectoparasitic Infections

Insects like fleas, sand flies and ticks act as vectors to pathogens like virus, bacteria or protozoa to cats and dogs. They are therefore, considered as potential health threat to their care givers and veterinary experts. Canine Vector-borne diseases (CVBD) and Feline Vector-borne diseases (FVBD)are terms used to describe the diseases transmitted through dogs and cats, respectively. The prime diseases under CVBD are rickettsiosis, tick borreliosis and canine leishmaniasis [7]. Ticks also pose serious health threat [8] to landscape developers and gardeners etc. particularly in Europe. Other pathogens spread by ticks include Anaplasma phagocytophilum, Borrelia burgdorferi, and Ehrlichia canis. Mosquitoes spread microfilariae of Dirofilaria immitis in dogs besides famously spreading malarial parasite.

Fungal Infections

Mycotoxins represent the only established non-viral occupational carcinogens [11]. Pulmonary cancers are reported in workers exposed to aflatoxin in industrial settings [12]. Denmark has previous incidences of liver cancer to workers during exposures to aflatoxin during farm work [13].

Stachybotrys chartarum is cellulolytic and causes soft rot of wood. It is usually found associated with damp straw and wall paper. It was first reported from wall paper in the city of Prague, the Czech Republic. Dampness attracts Stachybotrys chartarum, the most common allergenic fungi found indoors in offices, school, homes [14] and farms in countries like USA, Canada, Russia, Hungary, Bosnia Herzegovinia,Germany, France, North and south Africa. Air-borne fungi are found in very high concentrations of office archives. The four common fungi reported are Cladosporium sp., Aspergillus sp., Penicillium sp., Stachybotrys chartarum. Moulds belonging to these genera are also reported during grain loading and unloading. They are causative agents of farmer’s lung disease [15]. Dairy farmers are also prone to infection from Stachybotrys chartarum as the fungus has been found in dairy cattle shed [11]. Early reports suggest severe lung infection on exposure while handling straw. A recent report states presence of Stachybotrys chartarum chemotype in dried culinary herbs [16]. This indicates occupational exposure of farm workers and hospital staff to the fungus. Today, the infection has been controlled using building technology to control dampness.

Waste water treatment plants (WWTP) all over Europe have reported presence of filamentous fungi in the air and water samples from their sites. In a study of two Portuguese WWTP, Penicillium sp. was the most frequently isolated fungal genus (58.9%), followed by Aspergillus sp. (21.2%) and Acremonium sp. (8.2%), in the total underground area [17]. In a partially underground plant, Penicillium sp. (39.5%) was also the most frequently isolated, followed by Aspergillus sp. (38.7%) and Acremonium sp. (9.7%). Therefore, the workers of these WWTPs are at occupational risk to fungal infections.

A Podiatrist is also exposed to bioaerosols loaded with fungus and yeast causing respiratory distress [18].

Algal Infections

The toxins produced by algae adversely affect humans, aquatic animals and ecosystems.

Viral Infections

Healthcare workers, research staff particularly those who are pregnant are high risk populations for human immunodeficiency virus, hepatitis B virus, hepatitis C virus, varicella-zoster virus, herpes simplex virus, human parvovirus B19, cytomegalovirus, rubella, measles, enteroviruses, mumps and influenza. In a comparative review, 84% laboratory infections were through aerosols including lymphocyctic choriomeningitis virus infections, hantavirus and coxsackievirus infections while droplet and mucocutaneous were leading transmission modes for Severe acute respiratory syndrome (SARS) and influenza B, respectively [9]. The deadly SARS infection is caused by Coronavirus. The same study found 92% blood borne viral infections to be contracted while working in hospitals.

Encephalitis in animal farmers is caused by Nipah virus in pigs and Hendra virus in horses while Haemorrhagic fever with renal syndrome (HFRS) or pulmonary syndrome (HPS) in farmers and laboratory workers is caused by Hantavirus by infecting field rodents [10].

Protein Diseases

Prions are responsible for zoonotic variant of Creutzfeldt-Jakob disease in agricultural and laboratory workers. Meat and bone meal is a well-known source for prion disease. Meat processing industry caters packed meat to millions. Its by-product bone meal and discarded meat is used in making fertilizers, animal feed and as alternative fuel. Thousands of workers are employed in meat industry or those using animal feed or fertilizer made from meat and bone meal besides those employed in storehouses and transportation or those who work in power stations using fuel made from infected meat. All these workers are at great risk of exposure to prions which lead to a series of neurodegenerative diseases. Though certain procedures are used to minimize prions, none of them are foolproof [19].

Occupational pollinosis has been recorded in professional gardeners or green house workers rearing ornamental flowers like chrysanthemum or fruits like strawberries or to paddy farmers.

Occupational Diseases Caused by Chemical Agents

There is a range of chemical substances (Fig. 5) from pure elements to their oxides, sulphites, carbonates or radioisotopes which are either found naturally or are produced artificially like polymers. Acrylamides, solvents, organophosphate compounds like insecticides, organic, halogenous compounds and various gases are few high risk chemicals to which workers are exposed.

Fig. (5))

Indicative list of various chemicals and their derivatives either during manufacturing process or during use.

The workers might be exposed to a level well below the threshold value. But, continuous exposure to low doses of chemical