A FOURTH person is being treated for the potentially fatal lung infection Legionnaires' disease.
The latest case, a patient from South Croydon, was identified as having Legionella bacteria on Tuesday.
It follows three confirmed cases last week which prompted a joint investigation by Public Health England, Croydon Council and the trust which manages Croydon University Hospital, where the patients are being treated.
Laboratory tests established that two of those cases were different strains of the bacteria, leading investigators to conclude that they are not linked.
The fourth patient is not from the same part of the borough and is also thought to be a "sporadic case" with no connections to the previous three, doctors said.
They are awaiting the results of further laboratory tests to determine the most recent stain.
Dr Barry Walsh, a director of health protection for Publish Health England, said: "As is usual for all reported cases of Legionnaire's disease we have been pursuing all potential sources of infection and following standard protocol for investigating cases.
"This includes taking detailed histories of the movements of the patients to see if there are similar patterns which would indicate a local source of infection.
"There is no current link between any of these four cases which would suggest a common source of infection."
Legionnaires' disease is a relatively rare condition caused by breathing in contaminated water.
The bacteria is found widely in rivers and ponds, but can thrive in artificially heated water such as showers, baths or hot tubs.
Efforts to trace the source, or sources, of the infections have included samples being taken from cooling towers which doctors believe the patients may have visited.
A review is also being undertaken into six of the most recent cases of Legionnaires' to identify if there are any links with the four patients. There have been 15 cases of the disease in Croydon in the last five years.
There are between 300 to 400 cases in the UK each year, and the disease has a relatively high mortality rate of between five to 15 per cent.
Symptoms include headaches, muscle pain and a general feeling of being unwell, progressing to high fever, vomiting, diarrhoea and, later, difficulty breathing.
Croydon Health Services, the trust which manages the hospital in London Road, continued to decline to comment on the patients this week. One is understood to be a man in his fifties. If you are feeling unwell with any of the possible signs of Legionnaires' disease contact your doctor or call NHS 101
