Biological Agent Exposure Issues Biology Essay


A biological agent is a micro-organism a microbiological entity, capable of replication or of transferring genetic material, including those which have been genetically modified, a cell culture or a human parasite, which may be able to provoke any infection, allergy or toxicity. [1] Biological agent exposure issues are particularly important in healthcare facilities as it is the most likely setting for biologically hazardous material to be found and communicated between patients, workers and members of the public. Additionally, healthcare facilities, by their very nature are occupied by individuals with compromised immune systems due to illness and so extra caution must be taken to prevent the spread of infection as it may have more severe effects on such individuals. Healthcare facilities include hospitals, clinics, dental offices, out-patient surgery centres, birthing centres, and nursing homes. [2] This is not an exhaustive selection. Staff (medical and non-medical), in patients, out patients and members of the public in Healthcare Facilities are at risk of exposure to Biological Agents. Staff working in close contact with patients suffering from contagious diseases or in contact with biological samples for testing or disposal is especially at risk. A more extensive list should include Doctors, Dentists, Nurses, Scientists, Porters, Paramedics, Caterers, Clerical Staff, Maintenance and Housekeeping.

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Biological Agents can be broken into groups depending in the type or nature of the agent. This grouping varies from text to text and is not an official classification. In this document Bacteria, Viruses, Parasites and Prions are considered.

Bacteria are single celled organisms. Along with viruses they are the smallest living things on earth. The have dimensions of ~ 1mm (10-6 m) and exist in a variety of shapes and structures. The most common bacteria in healthcare facilities are MRSA (Methicillin-resistant Staphylococcus aureus), especially prevalent in long-term facilities such as nursing homes, Pseudomonas aeruginosa and Klebsiella pneumonia which cause pneumonia in patients with weakened immune systems, E. coli, VRE (Vancomycin-resistant Enterococcus faecium) and Acinetobacter baumanni, nicknamed 'Iraqibacter' due to reports of outbreaks in military hospitals in Iraq.

Viruses are smaller than bacteria with dimensions in the order of 1nm (10-9 m). Viruses depend on a living host. A virus injects genetic material into the cells of its host. An infected cell produces viral protein and genetic material instead of its usual products. In this way, more of the virus is formed, this bursts out of the host cell, killing the cell and infecting other cells. Some viruses such as Rhinovirus (cold), Chickenpox, Influenza and Shingles are very common, while others such as Polio, Ebola virus and AIDS are limited to smaller populations or geographical areas. Smallpox, a virus that was relatively commonplace as recently as the 1960's, has been eradicated though vaccination programs.

Parasites are organisms that derive nourishment and protection from other living hosts. They range in size from single cell 'protozoa' to 'helminths' which are parasitic worms up to 2m in length. Microscopic parasites include Leishmaniasis, Toxoplasmosis and Malaria while Fleas, Ticks, Flatworms, Tapeworms and Lice are macroscopic parasites.

Prions are abnormally folded proteins. In a host, the prions force healthy proteins to bend and become misshapen like the prions themselves. This begins a chain reaction of tissue damage and cell death. Because prions do not contain their own DNA (unlike the biological agents mentioned above) they stimulate no immune response in the host. Prions are also known as Transmissible Spongiform Encephalopathy (TSE), the most studied of these is Creutzfeldt - Jakob disease (CJD), the human analogy of BSE in cattle.

Significant routes of exposure to infection agents include ingestion, inhalation and skin and mucous membrane penetration.

Ingestion of pathogenic (disease causing) microbes occurs frequently as a result of poor personal hygiene and poor workplace practice. Handling infectious material without wearing gloves and failure to wash contaminated hands before handling food are some common mistakes. Eating, drinking, smoking and application of cosmetics or contact lenses in the vicinity of infectious biological agents can also result in ingestion of the agents or exposure to the conjunctiva (eyes).

Inhalation exposure occurs when aerosol generation procedures are conducting in an open are without containment. Many laboratory and ward procedures generate aerosols. Containment measures should be implemented to prevent exposure). Inhalation probably accounts for the majority of all occupational infections.

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Exposure frequently occurs as accidental injections with contaminated needles or cuts with contaminated sharp instruments.

An official classification of biological agents into 'Hazard Groups' exists and is part of Irish legislation. The hazard system is based on a number of factors; how likely the micro-organism is to cause disease, how contagious the disease is in the community, whether or not an effective treatment exists for the disease, the route of infection (e.g., air, blood) and if preventative measures, such as vaccines are available. Biological agents in groups 2 and above are listed in the Statutory Instruments No. 146/1994 and No. 248/1998 [3]. SI No. 248/1998 is an amendment to SI No. 146/1994 which introduces the Hazard Group 3*. The following is a brief description of each of the Hazard Groups;

Hazard Group 1; a micro-organism unlikely to cause disease.

Hazard Group 2; a micro-organism that can cause disease, might be a hazard, is unlikely to spread in the community but effective treatment available.

Hazard Group 3; a micro-organism that can cause serious disease, is a serious hazard, may spread in the community though there is usually effective treatment

Hazard Group 3*; certain biological agents classified in Group 3 which are indicated in the list (in the SI documents) by an asterisk (*), may present a limited risk of infection for workers because they are not normally infectious by the air-borne route.

Hazard Group 4; A micro-organism that causes severe disease, is a serious hazard can be readily spread and effective treatment and preventive measures are usually not available.

Some of the listed micro-organisms have an indication meaning that lists of exposed workers should be kept for over 10 years after possible exposure. It should be noted that this classification system assumes healthy individuals, i.e. does not account for pregnancy, immune system deficiency or any pre-existing illness.

In Ireland, the 'Safety, Health and Welfare at Work Act 2005' [4] outlines the general rules for workplace safety. It also details the duties and responsibilities of employers and employees which will be dealt in this document shortly. The previously mentioned Statutory Instruments 146/1994 and 248/1998 are specifically dedicated to issues arising from biological agent exposure. In the original SI document (1994), Section 11 deals briefly with Healthcare and veterinary in particular; Section 12 is to do with Laboratories, industrial processes and animal rooms since large hospitals usually have laboratory facilities on-site, both Sections 11 and 12 are relevant to this discussion.

From SI No. 146/1994; It shall be the duty of every employer to-

( a ) to avoid the use of a harmful biological agent, if the nature of the activity so permits, by replacing it with a biological agent which, under its conditions of use, eliminates or reduces the risk to the health of employees,

( b ) to prevent the exposure of employees to a biological agent at a place of work where the results of the risk assessment reveal a risk to employees' health and safety,

( c ) to ensure that the level of exposure of employees is reduced to as low a level as necessary in order to protect adequately the health and safety of the employees concerned, where it is not technically possible to prevent exposure,

( d ) to apply the measures specified in the legislation where the results of the risk assessment reveal that it is not technically possible to prevent exposure,

( e ) where the results of the risk assessment show that the exposure or potential exposure (or both) is to a group 1 biological agent, including live attenuated vaccines, with no identifiable health risk to employees to provide that where a biological agent is being handled as part of an industrial process, to ensure that the principles of good occupational safety and hygiene are applied,

( f ) where the results of the assessment show that the activity does not involve a deliberate intention to work with or use a biological agent but may result in employees being exposed to a biological agent, as in the course of the activities, to comply with Regulations, unless the results of such assessment show such compliance to be unnecessary,

( g ) to apply these Regulations to activities in which employees are likely to be exposed to biological agents as a result of their work.

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From the same Statutory Instrument; It shall be the duty of every employee to report to his employer or his immediate supervisor any accident or incident, of which he becomes aware, involving the exposure to, or release of, a biological agent likely to involve a risk to the health and safety of employees.

For biological agents, there are no TLVs (Threshold Limit Values) for exposure. Biologically derived contaminants are ubiquitous in nature. Humans are repeatedly exposed to a wide variety of such materials. There are no TLVs against which to compare environmental air concentrations of most materials of biological origin. The following discussion, taken from the ACGIH handbook on TLVs and BEIs [5], explores reasons for a lack of assigned TLVs. Culturable (bacteria and fungi that can be grown in a laboratory culture) and countable (bacterial cells that can be identified and counted by microscope) bioaerosols, are generally complex mixtures of many different microbial, animal and plant particles. Human responses to these bioaerosols range from innocuous to fatal diseases so an appropriate exposure limit is impossible to set for all bioaerosols. Additionally, a single sampling method does not exist for all bioaerosols, this leads to different estimates of bioaerosol concentration. Information is insufficient to describe exposure-response relationships. With respect to infectious agents, human dose-response data are available only for a few infectious bioaerosols. In most routine exposure settings, public health measures such as immunization, active case finding, and medical treatment, remain the primary defenses against infectious bioaerosols. Facilities associated with increased risks for transmission of airborne infectious diseases (such as healthcare facilities) should employ engineering controls to minimize air concentrations of infectious agents. Further, such facilities should consider the need for administrative controls and personal protective equipment to prevent exposure of workers to these bioaerosols.

In dealing with Biological agents, the hazards are exposure to biological agents through blood or bodily fluids or 'sharps' (e.g., needles) incidents. It is vital to properly identify the hazard. The activity dealing with biological agents is important to consider, as is the identifying the particular micro-organism(s). Knowledge of the biological agent and the process it's going through is the first part of undertaking a risk assessment. This is done by reviewing scientific literature, clinical studies and past epidemiological evidence.

According to SI No. 146/1994, an employer is obliged "to assess any risk to the health and safety of employees resulting from any activity….to a biological agent… lay down measures to ensure the safety and health ….." i.e., an employer must carry out and implement a risk assessment. The risk from a substance or activity is the likelihood that it will cause harm in the circumstances of use or that the hazard will be realised. This harm may be personal injury, damage to property, the environment, reputation or breach of regulation or professional standards. This procedure has to be carried out by someone who is experienced and familiar with the activity - a competent person. A risk assessment must be a written record including all biological agents and should be renewed regularly or when there is a change in the system or biological agent. The risk assessment should be based on the hazard classification, information available on the disease and the possible allergenic and toxic effects of the micro-organism

The HSA (Health and Safety Authority) recommends that a risk assessment should include information on the following; Severity, Likelihood of occurence, number of persons exposed and the ease of control.

The combination of Severity and Likelihood leads to the 'Risk Rating'. Severity is based on the consequences of an accident or incident on the following groups; Safety (staff, patients, population), Quality and professional guidelines, Fear/disempowerment and conflict of interest, Reputation, community expectation, Financial and Legal requirements.

Severity ranges over Low, Minor, Moderate, Severe to Catastrophic. The effect of a 'Low' severity incident would include minor cut or bruises, minor non-compliance of workers, some press coverage, minor cost, minor out of court settlement. On the other hand, a 'Catastrophic' event involves multiple fatalities or trauma, gross failure to meet professional standards, widespread organisational conflict, full public enquiry, maximum financial loss, criminal prosecution without defence. Likelihood is also ranked into five groups, they are; Rare, Unlikely, Possible, Likely, and Almost Expected.

Below is an example of a Risk Matrix. [6] It shows how the combination of high Likelihood and high severity indicates a very High risk but an unlikely, low severity event has a risk of 'effectively zero'.

The Hierarchy of Control is a list of control measures, in priority order, that can be used to eliminate or minimise exposure to hazards in the workplace. This preferred order of control is embedded in almost all Occupational Health and Safety legislation, standards and guidelines.[7]

Removal or elimination of the hazard is the ideal control situation. PPE is the least desirable means of control because the hazard remains and there is considerable reliance on providing the right equipment for the situation and on having the equipment worn correctly and consistently. It is expected that only when all practicable steps have been taken there should be a step down to the next level.

Engineering controls are implemented when the biological agent cannot be replaced or removed. Engineering controls have an effect on the physical surrounding of the biological agent, for example, robust and leak proof specimen/transport containers, anti-needle stick devices, puncture resistant sharps containers and negative pressure rooms.

Sterilisation is part of the engineering type of controls. It is the process of killing all living organisms. It can be done using dry heat, or a steaming device called an autoclave. To be fully sterilized, liquids are subjected to 121-124oC for 15 minutes and equipment must spend 3 minutes at 134oC. Disinfection is the killing or rendering inactive of pathogenic organisms. It is slightly less effective but still widely used. Choice of disinfectant depends on the micro-organism, surfaces to be cleaned and any health hazard associated with a harsh chemical disinfectant.

Administrative controls are the next preferred defence against exposure. Biological waste disposal system is an example of an administrative control. Biological waste is segregated into yellow bags and bins labelled with the Biohazard sign (right). Yellow containers with black lids are reserved for microbiological cultures which have NOT been autoclaved, in particular, blood or tissue suspected of being contaminated with CJD, hazard group 3 laboratory waste that has not been autoclaved.

Employee training is an important administrative control as education on proper hand washing and other hygiene practices lowers the chances of exposure and the spread of contamination.

PPE (Personal Protective Equipment) is the last line of defence against unwanted biological agent exposure. PPE in healthcare facilities is comprised of gloves, aprons, masks, eye protection, face protection, clothing protection or scrubs and possibly a white coat. Respiratory protection may be used when a hazard is expected, such as in an isolation unit of an infected patient. It is vital that PPE be properly fitted, maintained and cleaned. It should be hypoallergenic, especially disposable gloves, so as not to irritate latex allergy sufferers.

Other control measures include vaccines, these are only available for some biological agents and vaccination records must be kept. In case of incident, chemical showers and other emergency procedures should be in place and practiced regularly with training drills.


All internet sources checked on 12th March 2011

Safety, Health and Welfare at Work (Biological Agents) Regulations, 1994. Statutory Instrument No. 146/1994. (

Safety, Health and Welfare at Work (Biological Agents) (Amendment) Regulations, 1998. Statutory Instrument No. 248/1998. ( )

Safety, Health and Welfare at Work Act 2005. 10th Act of the Oireachtas of 2005. (

"TLVs and BEIs- 2009" American Conference of Government Industrial Hygienists (ACGIH). Signature Publications, 2009.