World Health Organization (WHO) - Classification of infective microorganisms by risk group (2003)
Risk Group I (low individual and community risk).
A microorganism that is unlikely to cause human disease or animal disease of veterinary importance.
Risk Group II (moderate individual risk, limited community risk).
A pathogen that can cause human or animal disease but is unlikely to be a serious hazard to laboratory workers, the community, livestock, or the environment. Laboratory exposures may cause serious infection, but effective treatment and preventive measures are available and the risk of spread is limited.
Risk Group III (high individual risk, low community risk).
A pathogen that usually produces serious human disease but does not ordinarily spread from one infected individual to another.
Risk Group IV (high individual and community
A pathogen that usually produces serious human or animal disease and may be readily transmitted from one individual to another, directly or indirectly.