Auckland's legionnaires outbreak - which contributed to the deaths of two people - has been declared over.
Auckland Regional Public Health Service said there were 17 confirmed cases of Legionella pneumophila (Lp1) between February and July, however confirmed cases has returned to its normal background rate, with only two cases confirmed over the past 78 days.
No source of the outbreak was found, although authorities believe it is possible there could have been numerous sources, given the geographical spread of cases.
The outbreak led to building owners being advised to shock dose their cooling systems and test for the presence of Legionella after three to seven days as a precaution.
Auckland Council building control manager Ian McCormick said an inter-agency working party which formed to deal with the outbreak, which includes public health and building industry groups, may advocate for legislative changes such as making it mandatory for building owners to log their cooling towers on a register and require owners to test for the presence of Legionella every month.
APRHS now has added the locations of all known cooling towers to a database.
Medical Officer of Health, Dr Simon Baker, said the outbreak increased awareness of risks and the need for improved surveillance of vulnerable water systems.
"Legionella bacteria occur naturally in the environment and can reach levels dangerous to people. The Lp1 sub-species is commonly found in warm water systems. This outbreak indicates that maintaining cooling tower surveillance and treatment is of paramount importance. Any systems that use stored water without heating or cooling sufficient to kill bacteria, need to be carefully monitored for Legionella presence, and treated if necessary," Dr Baker said.