Air-conditioning bug responsible for deaths every year

By MARTIN JOHNSTON health reporter

The bug that can cause the potentially fatal legionnaire's disease may lurk in up to 11 per cent of building air-conditioning towers, according to overseas estimates.

Legionella bacteria breed best in warm, moist conditions, such as those found in the cooling towers of "wet" air-conditioning systems that use water to cool air.

The disease's symptoms can include a headache, diarrhoea, aches, dry cough and drowsiness, although some people have only mild effects or no illness at all.

It is treated with antibiotics.

Around 50 cases are reported to New Zealand health authorities annually, including a few deaths. Internationally, the death rate is between 5 per cent and 30 per cent of cases.

The greatest risk is to people over 50 and heavy smokers.

Occupational hygiene specialist Garry Trotman, of the Occupational Safety and Health service, said British and American research indicated that up to 11 per cent of air-conditioning cooling towers might contain legionella.

But it was usually controlled by regular, automatic dosing with chemicals to kill it and the organisms it liked to grow on, or by "shock dosing" if testing showed it was present.

It was rare for buildings to be evacuated, as the police building in Otahuhu had been.

"It's a fussy organism and it doesn't grow that well," said Mr Trotman.

It liked slightly warm water and the presence of a "bio-film" of other organisms.

Weekly checks must be made on cooling-tower water quality as well as a six-monthly test specifically for legionella, Mr Trotman said.

There was no acceptable level of legionella in cooling towers. If any were found, the tower must be shock-dosed immediately and a check made for faults.

Towers were also commonly cleaned by water-blasting during the Christmas-New Year break to remove bio-film.

"The bottom line is that you don't want bio-film to build up because that can provide a medium for legionella to grow within."

Other Auckland buildings to have been hit by legionella are ANZ House in Queen St and Telecom's Airedale St building.

ANZ House was closed for more than a week in January 2001 and bank staff moved to other offices while an air-conditioning cooling tower was disinfected.

The bug was found in the Telecom building's cooling towers the following March, but the building was declared clean a few days later.

A serious legionnaire's disease outbreak occurred in 2000 when more than 100 people fell ill, including two who died, after visiting the newly opened Melbourne Aquarium. Its water cooling towers were infected.

A study published in the New Zealand Medical Journal that year found that legionella was present in the electrically heated hot-water systems of 6 per cent of Wellington homes tested and presumed to be present in a further 6 per cent.

Researchers had tested hot water and taken swabs from taps and shower heads.

Legionnaires

A form of pneumonia

Thought to be caught by inhaling infected water mist in some types of air-conditioning systems.

Other sources are whirlpool spas, showers, decorative fountains and contaminated soil or potting mix.