CAR washes have emerged as a new legionnaire's disease threat after seven people were admitted to hospital in the world's first reported outbreak at a car wash.

The Grand Car Wash in Hoppers Crossing has been closed for disinfecting and plumbing works while an investigation into the outbreak continues.

Health authorities have called an urgent meeting with representatives of the car wash and plumbing industries today to discuss the potential dangers posed by booming hand-held car wash businesses.

Victoria's chief health officer John Carnie yesterday said that more information was needed.

But legionella bacteria experts warned that commercial car washes springing up across Victoria may provide perfect conditions for outbreaks because they used recycled water, warm storage tanks and spray vapour.

All seven people struck down by the latest outbreak went to hospital between April 14 and May 15 after visiting the Old Geelong Rd car wash.

Legionella had never previously been linked with car washing businesses and it took until May 9 for an exhaustive investigation to pinpoint the cause, which has since been confirmed through five positive water samples.

The Grand Car Wash closed as soon as the link was made.

"They have been undertaking a lot of work with plumbing engineers to try and ensure we can all be satisfied they are no longer a public health risk," Dr Carnie said.

A water blaster used for cleaning boats in Auckland and a New York bus wash have been linked to legionnaire's outbreaks.

But the Hoppers Crossing business uses a different system and Dr Carnie said commercial car washes now had to be examined for the first time.

"Whether this is a one-off or something went wrong at that place is hard to determine," he said.

"We are using it as a means to have further discussions with the industry, but I would not be warning people away from using car washes because there has been no previous episode linked to a car wash.

"Once we know what kind of systems they have in place we might be able to come up with some simple advice."

Legionnaire's expert Michelle Critchley said car washes could be even more dangerous than cooling towers, because spray hoses produced droplets much more likely to spread the disease.