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12 BIOLOGICAL HAZARDS
12.1 Introduction to Biological Hazards
A fundamental difference between chemical and biological hazards is that biological agents, whether bacteria, viruses or moulds have the ability in the
right conditions to rapidly replicate themselves. This means that the focus on control is not only avoidance of contact with the agent, but also on ensuring
that conditions favourable for growth of the organism are prevented. The three main categories of biological agents that we will be covering
examples of, are bacteria, viruses and fungi. Bacteria - single celled micro organisms that live in soil, water and air.
There are many thousands of different types of bacteria – many are
harmless, or even beneficial, but some bacteria are pathogenic - that is they cause disease. Examples of diseases caused by bacteria include
Legionnaires disease, various types of food poisoning e.g. salmonella and anthrax. Antibiotics are used to treat bacterial infections.
Viruses – tiny parasitic organisms that can only reproduce within living cells. They consist of nucleic acids RNA or DNA with a protein coat.
Largest known virus approx 1000 x smaller than the average bacteria. Viruses cause many diseases including the common cold, influenza,
measles, rabies, hepatitis and AIDS. Antibiotics are ineffective against viruses but many viral diseases are controlled by vaccines.
Fungi – simple plants lacking chlorophyll and normal plant structures e.g. leaves, stems etc. Fungi include yeasts, moulds, mildews and
mushrooms. The response of each individual to exposure to micro-organisms depends on
his or her state of immunity, i.e. the power of the individual to resist disease. There are many factors involved in immunity including:
whether the individual has already experienced a particular illness immunisation levels
individual resistance fatigue
age
110 To simplify how risks from different organisms should be managed they are
categorised into different risk groups. Control measures required should be matched to the risk group:
Risk Group 1 - low individual and community risk. An organism that is unlikely to cause human or animal disease.
Risk Group 2 - moderate individual risk, limited community risk. A
pathogen that may cause human or animal disease and which might be a hazard to laboratory workers, but is unlikely to spread to 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 3 - high individual risk, low community risk. A pathogen
that can cause serious human disease but does not ordinarily spread from one individual to another.
Risk Group 4 - high individual and community risk. A pathogen that
usually produces serious human or animal disease and may be readily transmitted from one individual to another, directly or indirectly.
There are also four Biosafety levels which give the containment precautions which need to be used to control different biohazards. The levels of
containment range from the lowest biosafety level 1 to the highest at level 4.
Biosafety Level 1 – Little containment or segregation of the facility but
with precautions such as separation and labelling of waste materials.
Biosafety Level 2 – Staff have specific training in handling pathogenic
agents, access to the laboratory is limited when work is being conducted, extreme precautions are taken with contaminated sharp
items; and certain procedures in which infectious aerosols or splashes may be created are conducted in biological safety cabinets.
Biosafety Level 3 – All procedures involving the manipulation of
infectious materials are conducted within biological safety cabinets or other physical containment devices, or by personnel wearing
appropriate personal protective clothing and equipment. The laboratory
111 has special engineering and design features such as double-door
access zones.
Biosafety Level 4 – The facility is either in a separate building or in a
controlled area within a building. The facility has controlled ventilation maintaining it under negative pressure. All activities are carried out in
Class III biological safety cabinets, or Class II biological safety cabinets used with one-piece positive pressure personnel suits ventilated by a
life support system.
12.2 Legionella and Humidifier Fever 12.2.1 Legionella