Deaths similar to those of heroin-users in the State and in Scotland have been reported among intravenous drug-users in the US.
Health officials in the Bay Area of California warned hospitals in October of a "potentially deadly form of botulism injected into the body along with tar heroin".
Some eight heroin-users have died of a "mystery illness" in the State since May 1st, while seven more have been affected by the illness. Four remain in hospital. In Scotland, 16 deaths and 12 more cases of the illness have been reported since April.
Meanwhile, 12 clinics will remain open to assess clients over the weekend in the Dublin/Wicklow/Kildare region. And four senior counsellors from the Eastern Regional Health Authority's AIDS and Drugs Unit will man the emergency phoneline through the weekend, on a 24-hour basis.
The counsellors will report to the public health medicine department on Tuesday. At least four people were treated in Oakland and Hayward, near San Francisco, in October for "wound botulism", an infection which attacks the blood and nervous system, causing paralysis and death.
Dr Barry Simon, who treated cases at Highland Hospital in Alameda, said they appeared to be the result of contaminated drugs. "The bacteria likes to live in the tar heroin, usually from Mexico," he said.
Tar heroin is a semi-solid form of the drug which is melted for injection, whereas the heroin available in Ireland is powdered and dissolved in citric acid. An ERHA spokeswoman said officials did not think at this stage there was any connection between the US cases and those being investigated in Dublin.
More than 200 new addicts have sought treatment at the drug treatment clinics in the Dublin, Wicklow and Kildare region over the past week, while the ERHA announced plans on Thursday for the rapid expansion of its drug treatment services.
The three area health boards are appealing to local communities to "accept treatment facilities in their area for drug-users in their community".
Meanwhile, the Press Association in London last night reported that 14 cases of the illness have been found among injecting drug-users in England and Wales, seven of whom have died.
Emergency helpline 1800 459 459.