The Auckland region has been hit by a sudden increase in reported cases of a potentially fatal lung infection, prompting a health authority to ask for urgent treatment of building cooling towers and other industrial water uses.

The Auckland Regional Public Health Service said this afternoon that it had been notified of nine cases of legionnaires' disease in the past six weeks. The region's average number of cases is typically one or two every six weeks.

Legionnaires' disease is a form of pneumonia and is caused by a bacterium that is a common contaminant of water systems. It can be spread via fine mists of contaminated water. The cooling towers of air-conditioning systems have caused outbreaks of the disease. It can be treated with antibiotics.

Because of the spike in cases, the public health service is urging the owners and managers of all buildings that contain a cooling tower, or industrial processes that use water and generates aerosols, to arrange for immediate shock-dosing of these systems.

"Building managers have a responsibility to shock-dose their cooling systems with a suitable biocide which will eliminate any legionella bacteria present and reduce the spread of this disease," said medical officer of health Dr Simon Baker.

The people sick with legionnaires' disease are from all over the Auckland region, the public health service says. Because of the long incubation period of the disease, it may not be possible to find the source quickly.

Dr Baker said that because of the severity of legionnaires' disease, it was important that building managers acted quickly, to avoid unintentionally causing more people to become sick.

Legionella bacteria have been found in domestic hot water tanks and compost - leading to disease risks associated with inhaling infected water from a shower head, and while gardening.

A public health service investigation connected a 2006 outbreak of legionnaires' disease in the suburb of Beachlands, in which an elderly man died, to a water blaster at a nearby marina. The water blaster was upwind on the prevailing wind of the homes of four people who caught the illness.

"Aerosols containing legionella discharged to air by the marina water blaster may have infected some cases directly or may have seeded roof-collected rainwater systems," public health physician Dr Greg Simmons and colleagues said in a report on that outbreak in 2007.

"Some cases may have been exposed by contaminated bathroom showers. Roof-collected rainwater systems need appropriate design, careful cleaning and the maintenance of hot water temperatures at a minimum of 60 degrees C to reduce the chances of legionella multiplying."