BASIC PRINCIPLES IN OCCUPATIONAL HYGIENE

Day 3

12 - BIOLOGICAL HAZARDS

BIOLOGICAL HAZARDS

• Biological Hazards - bacteria, viruses or moulds have the ability in the right conditions to rapidly replicate themselves.

• 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.

BIOLOGICAL HAZARDS

The three main categories of biological agents:

• Bacteria - single celled micro organisms that live in soil, water and air.

• Viruses – tiny parasitic organisms that can only reproduce within living cells.

• Fungi – simple plants lacking chlorophyll and normal plant structures (e.g. leaves, stems etc).

Dividing Escherichia coli bacteria

Source: Wikimedia Commons

Exposure to micro-organisms

Individual to exposure to micro-organisms depends on state of immunity:

– whether the individual has already experienced a particular illness

– immunisation levels

– individual resistance

– fatigue

– age.

Legionella pneumophila multiplying inside a cultured human lung fibroblast Source: Wikimedia Commons

CONTROL DEPENDANT ON 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.

• 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.

Biosafety levels

Four Biosafety levels which give the containment precautions:– Biosafety Level 1 – Little contaiment or segragation, precautions such as

seperation and labelling of waste materials.

– Biosafety Level 2 – Staff have specific training in handling pathogenic agents, restriocted access, sharps protection, biological cabinets for certain activities

– Biosafety Level 3 – Bbiological safety cabinets or other physical containment devices, personal protective clothing and equipment. Double-door access zones.

– Biosafety Level 4 – Separate building/ controlled are. Controlled ventilation maintining it under negative pressure. All activities are carried out in Class III biological safety cabinets, or Class II biological safety cabinets with one-piece positive pressure personnel suits ventilated by a life support system.

Legionella

X5000 Magnification of a large grouping of Gram-negative Legionella pneumophila bacteria Source: Wikimedia Commons

Legionella

• 1976 - an outbreak occurred among delegates attending an American Legion convention.

• Two patterns of disease in humans;

– Pontiac Fever (a mild flu-like illness)

– Legionnaires Disease. (pneumonia and flu-like symptoms. It is fatal in about 10 - 15% of cases).

• It enters into the body when fine droplets of contaminated water are inhaled. The bacterium is not transmitted from person to person.

• Legionella are widespread in natural fresh water including rivers, lakes, streams and ponds.

Legionella

Areas most at risk include:– Cooling towers

– water storage tanks and calorifiers

– hot and cold water services in premises where occupants are particularly susceptible (homes for the elderly, hospitals etc.)

– humidifiers and or washers that create a spray of water droplets and in which water temperature exceed 20°C

– spa baths and pools

– fire sprinkler systems and fountains.

Legionella

Factors affecting growth include:

• Water temperature - Temperatures in the range of 20-45°C favour growth (optimum temperature 37°C). Proliferation of the bacteria is unlikely below 20°C, and the organism does not survive above 60°C.

• Water being stagnant favours multiplication.

• The presence of sediment, scale and sludge.

• The presence of other micro-organisms (algae, amoeba and bacteria) or a biofilm (a layer of micro-organisms contained in a matrix which may form a slime on surfaces).

Legionella

Control – prevent growth of bacteria and production of aerosols

• Minimise the release of water spray

• Avoid water temperatures between 20°C and 45°C

• Avoid water stagnation

• Avoid use of materials that can harbour or support the growth of bacteria and other organisms

• Keep the system clean

• Use of suitable water treatment systems including biocides

• Ensure that the system operates safely and correctly and is well maintained.

• Sampling to assess water quality.

Humidifier Fever

• Associated with exposure to many different types of micro-

organisms including various bacteria and fungi found in humidifier

reservoirs and air-conditioning units.

• The micro-organisms have been found in both large ventilation

systems as well as in small units.

• Significant concentrations of these organisms can be dispersed

into the environment in the aerosol mist generated by the

humidifiers during normal operation.

• Flu-like illness with fever, chills, headache, muscle ache and

fatigue.

• Controls by ensuring that the bacteria and fungi do not multiply.

Blood Borne DiseasesThe risk of occupational acquisition of a blood borne virus relates to:

– The prevalence of the virus in the patient population– The efficiency of virus transmission after a single contact with infected

fluid / tissue– The nature and frequency of occupational blood contact– The concentration of the virus in the blood.

Protection comes from avoidance of blood to blood contact by precautions including:

– Wearing protective gloves and face masks– Covering cuts and wounds with a waterproof dressing– Care with sharps– Ensuring all equipment is appropriately sterilized– Safe disposal of infected material– Control of surface contamination– Good hygiene.

Blood Borne Diseases• Hepatitis B

• Hepatitis C

• HIV - (Human Immuno-deficiency Virus).

Zoonoses• Zoonoses are infections that are naturally transmitted from animal to

humans.

• There are over 150 known zoonoses which range from ring worm to anthrax and rabies.

• Zoonoses primarily affect people who work closely with animals i.e. farm workers, laboratory workers, vets, forestry workers.

• Infection can occur through contact with:– Animal and animal products (meat, bone meal, fur, feathers, skins, wool)– Animal tissue & body fluids (blood, saliva etc)– Birth products (placenta etc)– Waste products (urine, dung, faeces)– Contaminated materials (ground, fencing, clothing etc).

• Infection may occur via inhalation, ingestion or through broken skin or contact with mucous membranes.

Anthrax• The disease is caused by the spore forming bacteria

Bacillus anthracis.

• Many animals may carry the anthrax bacteria or spores including cattle, horses, goats and sheep.

• Spore remain viable in animal products for long periods.

• Cutaneous anthrax - (a skin disease).

• Pulmonary anthrax (affecting the lungs).

• The main occupations at risk include agricultural workers, abattoirs, animal by product processing, vets and the wool and tanning industries.

Source: Wikimedia Commons

Leptospirosis • The main form of leptospirosis is Weil’s

disease which is a potentially life

threatening illness caused by the

Leptospira bacteria passed from rats via

urine.

• Symptoms include flu-like symptoms

such as fever, headache, vomiting,

muscle pains, pneumonia and possible

kidney failure and death.

• The disease may be transmitted through

contact with rat’s urine or watercourses

contaminated with it.

Source: Wikimedia Commons

Salmonellosis• Salmonellosis is the name given to an infection caused by any of

the Salmonella group of bacteria.

• Salmonella bacteria may be carried by most types of farm animal.

• Symptoms develop suddenly about 12 to 24 hours after infection

and include malaise, headache, nausea, abdominal pain,

diarrhoea and fever.

Pandemics

An epidemic of an infectious disease that spreads over a wide geographic area and affects a large proportion of the population.

A pandemic can start when the following conditions occur:

– Emergence of a disease, or a particular strain of a disease, new to a population

– The agent affects humans, causing serious illness

– The agent spreads easily and sustainably among humans.