Three people have died from a killer form of meningitis in the last two weeks.
A spike in cases of the lethal bug has seen 11 people fall ill over Christmas and the New Year in Dublin and other regions.
Health officials warned of a steep rise in meningococcal meningitis and septicaemia over the festive season.
Parents have been warned to be alert for symptoms and to seek urgent medical help in the event of a young child or adolescent falling ill.
HSE public health specialist Dr Suzanne Cotter said: "All age groups have been affected, ranging from infants to elderly. Of the three patients who died, two different strain types were identified."
The speed of the infection, which can be confused with cold or flu, makes it one of the most feared illnesses by parents and doctors.
Dr Cotter added: "Parents of children should also check that they are up-to-date regarding their childhood meningococcal vaccinations."
There has been a fall in the uptake of meningococcal vaccines among children in recent years, leaving thousands at risk.
It comes as hospital accident and emergency departments continued to struggle with high levels of overcrowding yesterday as 565 patients waited on trolleys for a bed.
The HSE said that following investigation none of the patients with meningococcal disease has been identified as having had contact or links with each other. They live in different areas of the country.
The 11 cases of meningococcal meningitis and septicaemia recorded in the last two weeks compare to just five for the same period last year.
In all of 2018 there were 89 cases notified compared to 76 in 2017.
Commenting on the increased meningitis threat Dr Suzanne Cotter, public health specialist at the Health Protection Surveillance Centre, said: "Although meningococcal disease incidence generally increases in the winter months, the recent increase is cause for concern.
"The HSE wishes to alert the public to the signs and symptoms of this disease so that immediate medical attention can be sought if someone has symptoms.
"If anyone has any concerns about meningitis they should ring their GP in the first instance. Meningitis and septicaemia often happen together and symptoms can appear in any order. Some may not appear at all.
"Parents of children should also check that they are up-to-date regarding their childhood meningococcal vaccinations."
A vaccine that protects against meningococcal C disease (MenC vaccine) is given after six months and at 13 months, and meningococcal B vaccine (MenB vaccine) is offered at two, four and 12 months.
Signs and symptoms may include:
The HSE advises that if anyone has any concerns or is showing symptoms of meningitis, they should contact their GP in the first instance but ensure that medical expertise is sought.
Young children and adolescents are at highest risk.