The investigation is across seven local authority areas Health officials are trying to find the source of a Legionnaires’ disease outbreak which has been linked to the death of a 64-year-old woman.
Another 13 people in south Wales are being treated for the disease and 11 of the cases are said to be linked.
The outbreak is clustered around the Heads of the Valleys corridor but no common link had yet been found between the cases.
The woman died in hospital on Monday, said Public Health Wales.
It has not yet been confirmed whether she died from Legionnaires’ disease.
Public Health Wales (PHW), the Health and Safety Executive and seven council areas are investigating.
Dr Brendan Mason, the consultant epidemiologist for Public Health Wales, told BBC Radio Wales: “The critical thing is to find source so it can be removed and then no-one else is put at risk.
“We need to look very carefully at the precise movements of the cases in that period before they became unwell and we then look for common links between them in an attempt to narrow down the search for a source.”
He said no common source had yet been found.
“It can be very difficult to tie down the source. A number of outbreaks are investigated and the source is never found”
Dr Brendan Mason Public Health Wales
“You are then looking at sources like cooling towers that under the right atmospheric conditions can disseminate this organism over very wide areas, many miles in fact,” he said.
He said PHW as well as the Health and Safety Executive, and local authorities were now looking at cooling towers and industrial areas in the Heads of the Valleys corridor for the source.
“It can be very difficult to tie down the source. A number of outbreaks are investigated and the source is never found. If something causes a problem now, there is potential it won’t in the future.”
Information has been circulated advising GPs of the steps to be taken if patients report symptoms.
Earlier Dr Jonathan Richards, a GP based in Merthyr Tydfil, one of the communities within the outbreak area, told BBC Radio Wales that it was important to to know what the link between the 11 cases might be.
Dr Gwen Lowe of Public Health Wales reveals details of the Legionnaires’ disease outbreak in south Wales.
He added: “It’s a serious disease that can people who are vulnerable. It rarely kills healthy people.”
Hugh Pennington, emeritus professor of microbiology at the University of Aberdeen said Legionnaires’ was “an infection that hits the elderly hardest”.
He said: “People who have pre-existing lung disease or heart disease, or have diabetes, have the hardest time with Legionnaire’s disease.”
Prof Pennington said it was important to remember that the disease did not “pass from person to person”.
He said: “There are various antibiotics that do work quite well. But in a minority of cases the antibiotics don’t keep the bug at bay so early diagnosis is quite important.”
Legionnaires’ disease begins with flu-like symptoms and can lead to pneumonia, usually in adults.
Anyone worried about their health should contact their GP.
The councils involved in the investigation include Cardiff, Merthyr Tydfil, Rhondda Cynon Taf, Caerphilly, Blaenau Gwent, Torfaen and Monmouthshire.
The outbreak control team, which also includes representatives from Cwm Taf Health Board, Aneurin Bevan Health Board, and Cardiff and Vale University Health Board, will continue to monitor the situation closely.
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