Agent or material-specific factors
Hazardous biological work can roughly be of two types. One is where a known hazardous biological agent such as a bacterium, virus, fungus, parasite, prion or viroid or a hazardous biological toxin is handled during the course of research or teaching work.
The other is when diagnostic, clinical, environmental, food, or any other type of sample that has the potential to harbour any hazardous biological agent or toxin is handled. For example, human blood could potentially harbour agents such as Hepatitis B, HIV while samples collected from birds may harbour human infectious influenza strains. Environmental samples like raw milk has the potential to include human infectious agents such as pathogenic strains of E. Coli, Salmonella and Campylobacter. It is always prudent to err on the side of caution and handle these samples with the same kind of controls as when handling known biological agents or toxins, unless the samples have been screened and have been shown to be free of these hazards. Therefore whenever an unscreened diagnostic, clinical, environmental, food or any other type of biological sample is handled, the biological agents or toxins that could potentially be present in that type of sample need to considered to facilitate an accurate risk assessment and come up with appropriate risk control measures.
There are a number of factors that need to be considered when conducting an agent or material specific risk assessment. These are described below:
Most countries have categorized microorganisms or biological agents into 4 categories known as risk groups based on the risk these microorganisms or biological agents pose to individuals, the community and the environment. AS/NZS 2243.3:2010 gives risk groupings for three types of microorganisms. These are
- Human and animal infectious microorganisms
- Plant infectious microorganisms
- Invertebrates carrying microorganisms
The four risk groups that come under each type are defined in AS/NZS2243.3:2010 in the following manner:
Human and animal infectious microorganisms
Plant infectious microorganisms
Invertebrates carrying microorganisms
Risk Group 1
A microorganism that is unlikely to cause human or animal disease.
(low individual and community risk)
A microorganism that is unlikely to be a risk to plants, industry, a community or region and is already present and widely distributed.
Microorganisms that are carried by invertebrates where the microorganisms are unlikely to be a risk to humans or to the environment and are already present and widely distributed.
Risk Group 2
A microorganism that is unlikely to be a significant risk to laboratory workers, the community, livestock, or the environment; laboratory exposures may cause infection, but effective treatment and preventive measures are available, and the risk of spread is limited.
(moderate individual risk, limited community risk)
A microorganism that is a low to moderate risk to plants, industry, a community or region and is present but not widely distributed.
Microorganisms that are carried by invertebrates where the microorganisms are a low to moderate risk to humans or to the environment and are present but not widely distributed. They have a limited ability to disperse because of low persistence of the microorganism outside the host. They are carried by invertebrates that are unlikely to be able to disperse or can be readily controlled.
Risk Group 3
A microorganism that usually causes serious human or animal disease and may present a significant risk to laboratory workers. It could present a limited to moderate risk if spread in the community or the environment, but there are usually effective preventive measures or treatment available.
(high individual risk, limited to moderate community risk)
A microorganism that is a significant risk to plants, industry, a community or region and is exotic but with a limited ability to spread without the assistance of a vector.
Microorganisms that are carried by invertebrates where the microorganisms are a significant risk to humans or to the environment and are exotic and have the ability to disperse with or without the aid of a vector. They are carried by invertebrates that are able to disperse.
Risk Group 4
A microorganism that usually produces life-threatening human or animal disease, represents a significant risk to laboratory workers and may be readily transmissible from one individual to another. Effective treatment and preventive measures are not usually available.
(high individual and community risk)
A microorganism that is a highly significant risk to plants, industry, a community or region and is exotic and readily spread naturally without the assistance of a vector.
Microorganisms that are carried by invertebrates where the microorganisms are a highly significant risk to humans or to the environment and are exotic and readily able to disperse with or without the aid of a vector. The microorganisms may be carried by invertebrates that are difficult to detect visually.
AS/NZS224.3: 2010 gives the risk group for a number of microorganisms or biological agents. In addition, other internationally recognised biological safety references such as the Risk Group Database given by the American Biological Safety Association (ABSA) can be used to determine the risk group.
Strain / Type of the agent
When working with a hazardous microorganism or biological agent, information about the exact strain is important as some strains may be more or less virulent than the wild type strain due to many factors. Some strains may also show host specificity. Therefore the risk of infection and the stringency of the controls needed would vary based on the pathogenicity of the actual strain handled.
Infectious dose and the stability of a biological agent in the environment
Although infectious doses for all biological agents is not always available and could depend on other factors, it is generally accepted that agents that have a low infectious dose pose a higher risk than those with a higher infectious dose.
If a biological agent has the ability to resist environmental stresses and survive outside a culture medium for a long time this will increase the chances of its ability to pass onto a suitable host.
Concentration and volume of the agent / material handled
Pure cultures of biological agents or isolates that have been propagated to high titres pose an increased risk of infection upon exposure, than clinical or environmental samples that may include a lower number of the same pathogenic biological agents.
Generally speaking, higher the volume of a biological material or agent handled, higher the risk of exposure would be.
Routes of exposure
Information about the natural route of infection and other routes of exposure that could result due to laboratory manipulations is important in deciding the appropriate controls that need to be implemented when handling infectious biological agents or material. It is important to remember that factors such as high volume and / or concentration of the material / agent handled, frequent use of a procedure that increase exposure risks can help infectious microorganisms or biological agents to overcome natural barriers and cause an infection through a route that is normally not associated with it. For example, high titre cultures of some arboviruses may be infectious through the respiratory route or through breaks in skin although the natural route of transmission for these viruses is through an inset bite.
Note: Resources such as Pathogen Safety Data Sheets available from the Public Health Agency of Canada, Agent Summary Statements given in the 5th edition of the Biosafety in Microbiological and Biomedical Laboratories (BMBL) can be used to find out more details about microorganisms while resources such as scientific literature, reports published by responsible authorities can be used to find out the potential microorganisms associated with various biological samples like specific human and animal tissues, environmental, food and other samples of a biological origin.