A second Legionnaires' patient has died but the disease outbreak in north and west Melbourne is "stabilising".

A man in his 60s died on August 1 after being admitted to hospital on July 27, Victoria's chief health officer says.

As of Sunday, there are 77 confirmed patients while test results for seven suspected cases are due soon.

"In the last 24 hours, we've seen an increase of two cases, and that's compared with an increase of 24 a few days ago," Chief Health Officer Dr Clare Looker told reporters.

"This strongly suggests that the number of cases is decreasing and the situation is stabilising."

About 75 of the confirmed cases and all of the suspected cases have been hospitalised.

Victoria's Department of Health has not yet confirmed the origin of the outbreak, but it has said the source is most likely linked to a water cooling tower in the Derrimut and Laverton North area, which is where investigations are focusing.

"Already our teams have visited and inspected and tested 54 of the highest-priority sites with cooling towers," Dr Looker said.

"While we've not yet identified a single cooling tower, there is a high likelihood that we have already tested and treated the source."

The department's investigation has found no link between the outbreak and a recent industrial fire in Derrimut.

It also found no evidence to suggest Legionella outbreaks are directly caused by large industrial fires.

The department is working with the Bureau of Meteorology and air scientists to understand how weather patterns in July might have contributed to the outbreak.

Victorians experiencing a chest infection should make sure they seek medical care, Dr Looker said.

People most at risk are adults aged over 40 years, especially those with other medical conditions, people who are immunocompromised, or those who smoke.

With AAP.