Children under 10 have been the main victims of Galway's contaminated public water supply, and three cases have been so serious that they have required treatment in dedicated children's hospitals.
The strain of cryptosporidium parasite found in human sewage has also been detected in about 75 per cent of samples analysed to date, according to the Health Service Executive (HSE) West's public health department.
Some 210 laboratory-confirmed cases of the gastrointestinal illness cryptosporidiosis have been recorded since the beginning of the year. However, up to 2,000 people may have been infected by the parasite and may not have submitted samples or sought medical help, HSE West public health officials have acknowledged.
The illness is continuing to affect people in Galway city and county, with some 15 confirmed cases last week reflecting a slight increase on the previous week. Of 40 cases requiring hospitalisation to date, some 24 of these involved children and 10 involved adults.
The detailed analysis of cases to date was issued at a briefing at HSE West headquarters in Merlin Park Hospital, Galway, yesterday, when it was emphasised that the "boil water" notice would not be lifted until the end of June at the earliest.
The HSE West, which believes it is handling an epidemic, will not lift the notice until there is a marked decline in cases of the disease, until there is an effective water treatment system in place to remove the parasite, and until water is clean, safe for human consumption and of "acceptable quality" in a "robust" system, it has said.
While Galway city council has been keen to forecast a clean supply by mid-June, the HSE West said yesterday that it would take at least two to four weeks, and perhaps "considerably longer", for any system to be deemed safe after completion of engineering works.
The city and county councils hope to have effective treatment systems for cryptosporidium by June 15th at the Terryland waterworks in Galway city and between June 7th and 15th in Luimnagh. Some scientists have said that 100 per cent removal of the parasite cannot be guaranteed, and that filtration systems are prohibitively expensive in large scale treatment systems.
The HSE West analysis of disease patterns has found that all age groups and approximately equal numbers of males and females have been affected, with most under the age of 10. The majority either live in Galway city or have contact with the city through work, school or socialising.
Some 98 human samples typed to date showed cryptosporidium hominis (associated with sewage) in 71 cases, and cryptosporidium parvum in 14 cases, while the remainder were "indeterminate".