To aid in risk assessment, the National Institute of Health (NIH) and World Health Organization (WHO) have developed a ranking mechanism to categorize microorganisms by:
- its capability to infect and cause disease in a susceptible human or animal host,
- its virulence as measured by the severity of disease, and
- the availability of preventive measures and effective treatments for the disease.
These categories are called Risk Groups.
Risk groupings (RGs) are used to characterize the relative risk associated with a given agent based on potential routes of transmission, susceptibility of healthy adult population to infection, and disease morbidity and mortality characteristics.
Most of the labs you will inspect will have only Risk Group 1 or 2 agents, the exception to this is HIV which is classified as RG-3, but in a research lab setting can be safely worked with at BSL-2 with some procedural enhancements like double gloves and limited sharps use.
Many organizations have assigned Risk Groups (RG) to specific biological agents. While the assigned risk group may not be identical for any given agent across all organizations, all use a four-group system with the lowest risk agents assigned to Risk Group 1 and the highest risk agents assigned to Risk Group 4.
- RG4 agents are infectious by all routes of exposure, have extreme mortality/morbidity rates, treatment is usually not available, and agents in this group present a high community risk. Risk of death following infection with a RG 4 agent is high.
- RG3 agents are infectious by all routes of exposure (especially the AIRBORNE route) and have higher morbidity and mortality rates than Risk Group 2 agents. Treatment may/may not be available. They generally present a high individual risk, but much lower community risk.
- RG2 agents are generally transmitted via ingestion, through mucous membranes, and through the skin. The severity of disease is usually not as significant as agents in higher risk groups, and treatment is generally available. Mortality and morbidity is lower than high risk group classifications.
- RG1 agents are not associated with disease in healthy adults.
To simplify, think of the RG Classification like this:
- “RG1 – Don’t Drink it”;
- “RG2 – Don’t Touch it”;
- “RG3 – Don’t Breathe it”;
- and “RG4 – Don’t do it at UNL!”
A couple of important points to remember:
- RG classifications consider only a healthy adult population.
- Risk Groups do NOT account for agents that may have greater or lesser virulence acquired through genetic modification or passage.
There are currently no risk group classifications for animal pathogens or plant pathogens in the US, although some foreign governments have established these classifications. So the risk assessment for those agents is different than for human and zoonotic pathogens.
There can be strain variation among species. An example is E. coli where there are lab adapted strains that are non-pathogenic and other strains such as O157 that are pathogens and the difference between these is based on the genes expressed.