The prevention and control of legionella at an Essex hospital remains a "significant concern", according to a health care watchdog.
The Care Quality Commission (CQC) said Basildon University Hospital had taken several measures to combat the disease, but further improvements were needed.
It said three people had acquired the disease while at the hospital in 2011.
The hospital's trust said it was already taking further steps to address the issue and other areas of concern.
The report followed a recent inspection on 9 February.
It said there had been a history of people catching legionella at the hospital, citing 13 cases since 2002.
'More attention needed'
The most recent cases were in August, September and November 2011.
The report said the hospital had made an "investment in measures to control legionella" including the introduction of a silver and copper ionisation disinfection system, to replace its chlorine dioxide one.
It added a legionella management group met once a month and the hospital worked with several other agencies regarding the outbreaks.
Despite this, the CQC said it was disappointed there were still cases arising and the trust needed to do more to reduce the risk of re-occurrence.
The report said people it spoke to were satisfied with their care and found the hospital was currently meeting standards in 13 criteria, but improvements were required in three.
It also identified moderate concerns over staffing levels and safeguarding patients from abuse.
Basildon and Thurrock University Hospitals NHS Trust said it welcomed the number of positive comments and praise for areas it had improved.
Chief executive Alan Whittle said: "We have said before there will always be room for improvement.
"What is reassuring is there were no surprises in the report. In many ways it reflects our own assessment of where more attention is needed."
He added the board had already approved investment in all three areas "to ensure they happen swiftly".
The CQC has given the hospital trust two weeks to set out the further action it intends to take.