AIR CONDITIONER FILTER MATERIAL SIZE 640 X 790 mm

Air quality

 Bacteria and viruses

Bacteria are ubiquitous in the air and general environment. They can cause adverse human health effects and deterioration of building materials when they proliferate in indoor environments (Stetzenbach 1998). The health effects of bacterial exposure in indoor air will depend on the species and the route of exposure.

The bacteria in building air can come from airborne sources from the wind’s action on soil and vegetation, compost, municipal landfills, sewage sludge, etc. They can also be a direct result of human activity, such as breathing, coughing and sneezing, or they may colonise the ductwork of the cooling systems, the water cooling towers (eg Legionella spp) or interior building materials and furnishings such as wallboard, wallpaper and flooring (Bates 2000).

In indoor environments, bacteria usually grow in areas with standing water such as water spray and condensation areas of air conditioning systems (Stetzenbach 1998). Dirty or poorly maintained air handling systems can become contaminated over time by bacterial populations that thrive on moisture-laden surfaces caused by water condensation. Legionella is probably the most common group of bacteria mentioned in association with airconditioning systems (see below).

Viruses are important airborne organisms and a significant contributor to occupational absenteeism. Examples of important viruses include the causative agent of the common cold (rhinoviruses) and the flu (influenza viruses types A, B, C, etc). The spread of these illnesses can be aided by inadequate ventilation levels within a building (Stuttard 1996). Viruses cannot multiply outside the human host, but can survive and remain infective for extended periods in the warm recirculating airspace of the modern air-conditioned building.

Routine testing for airborne viruses is expensive and not generally recommended. However a useful correlation between the levels of some airborne bacteria, particularly the Micrococcus group, and poor ventilation levels has been noted, and these can thus be used as an indicator of potential cross-infection problems (Stuttard 1996).

Prevention and control of legionnaire’s disease in Australia

Legionella bacteria are common microorganisms of concern. They occur naturally in small numbers within soil and water. However, the danger occurs when the bacteria are present in warm, moist environments such as cooling towers in air-conditioning plants, where they can multiply rapidly. Evaporative air conditioning units such as those used in homes and many business premises are not a likely source of legionella infection.

Most legionella infections are contracted outdoors, but predominantly in areas associated with cooling tower systems used to treat indoor air. Legionella infection control must therefore be included in discussions about indoor air quality. Legionella outbreaks have been recorded as a result of building air inlet pipes being positioned directly underneath air outlet pipes (Bates 2000).

As noted in the State of the Environment report (DEST 1996), inhalation of droplet aerosols (very fine droplets of water) containing legionella bacteria can cause legionnaire’s disease. Sources of droplet aerosols include spray drifts vented from cooling towers into the atmosphere.

Poorly maintained spa pools can also be a source of legionella infection. Spas are normally heated to about 37°C and use air and water jets to produce turbulence. These conditions result in rapid growth of undesirable organisms, including legionella. These organisms may be transmitted readily to humans by inhalation of the aerosols created by the air and water jets.

In recent years there have been reports of legionnaire’s disease cases associated with the use of potting mix. Australian studies have found legionella species present in over 70% of commercial potting mix samples. The route of transmission of the bacterium from potting mix is not clearly established and is the subject of further studies.

Legionnaire’s disease is a rare form of pneumonia with a relatively high mortality rate of up to 20%. It represents 1% of pneumonia cases in Australia, with around 180 cases a year reported nationally. The most serious outbreak in Australia occurred in 1987 in Wollongong, when 44 cases were reported and 10 deaths resulted. Early symptoms resemble those of flu and include headache, fever, chills, muscle aches and pains and generally a dry cough followed by shortness of breath. Other body systems can sometimes be affected, resulting in diarrhoea, mental confusion and kidney failure. Legionnaire’s disease can be a very serious illness, particularly in the elderly, heavy smokers, people with respiratory diseases and people with an immune deficiency.

Currently, there is no vaccine for preventing legionnaire’s disease and total eradication is impossible because legionella is widespread in the environment. Instead, control measures aim to prevent exposure by preventing the growth of legionella in cooling towers, warm water systems and spas. Control mechanisms consist of regular maintenance, including chemical treatment.

The Australian Commonwealth, States and Territories do not have a common regulatory approach to the control of legionella. The National Environmental Health Forum (NEHF) has produced guidelines for the control of legionella (see below). The NEHF publication Water No. 1 Guidelines for the Control of Legionella includes an appendix on the regulatory approaches by Australian States and Territories.

AS/NZS 3666.3:2000 outlines a performance-based approach to the maintenance of cooling water systems and for the control of Legionella spp and other microorganisms in such systems. This approach combines automatically regulated water treatment with monitoring, assessment and control strategies to help create a low-risk environment in the cooling water system.