The HSE West has discovered that 19 of 24 samples of cryptosporidium taken from sick patients in Ireland showed that the bug is of human origin, rather than animal.
The bug has affected the drinking water of 90,000 residents of Galway city. The HSE reported to RTE News that this new evidence does not confirm that the parasite outbreak was primarily caused by sewage. Further samples will be taken and sent to a lab in Swansea.
An investigation has also revealed that the Sewage Treatment Plant in Oughterard, Co Galway, is a source of the cryptosporidium outbreak on Lough Corrib.
Residents of Galway city and county have been under a boil order for three weeks while officials attempt to provide an alternative water supply.
Laboratory analysis has proven that emissions from the 60-year-old sewage plant are eight times in excess of permissible levels of the parasite. The cryptosporidium levels are also 60 times in excess of internationally accepted emissions.
Galway County Council officials reported that the plant's emissions strictly complied with EPA limits. However, the Council's Director of Services reported that the plant had failed half of the tests conducted over the last five years.
The cryptosporidium parasite causes severe stomach pains and diarrhea and has made more than 120 people in the area ill. Experts believe that the contamination and boil alert could last for up to six months.