The HSE has issued a warning to the public following the death of two people after contracting meningococcal meningitis/septicaemia.
Four cases of the condition are being investigated by the HSE. Three cases are confirmed and one is possible.
In two cases the people affected have died since their condition was reported in the last week of September.
Three of the cases are young adults, and one is a child under ten.
The cases were reported from different regions of the country and have no known links with each other.
Close contacts are being identified by public health and will be provided with antibiotics to prevent infection and will also be offered a vaccine if appropriate.
A HSE spokesperson said meningitis is a "serious illness" that involves "inflammation of the membranes covering the brain and spinal cord."
"It can be caused by a variety of different germs, mainly bacterial and viruses. Bacterial meningitis, such as in these cases, is less common but usually more serious than viral meningitis and requires urgent treatment with antibiotics.
"Bacterial meningitis may be accompanied by septicaemia (blood poisoning). The bacteria live naturally in the nose and throat of normal healthy persons without causing illness.
"The spread of the bacteria is caused by droplets from the nose and mouth. The illness occurs most frequently in young children and adolescents, usually as isolated cases. Bacterial meningitis or septicaemia requires urgent antibiotic treatment," they added.
Meningitis and septicaemia can often happen together. The symptoms can appear in any order and some may not appear at all. Symptoms include:
- Neck stiffness
- Discomfort from bright light
- Muscle pain
- Stomach cramps
- Fever with cold hands and feet
- A rash may appear, which looks like pin-prick type marks which if untreated can spread to form bruises or blood blisters.
The HSE advises that no one waits for a rash to appear if they are experiencing symptoms. "If someone is ill and getting worse, get medical help immediately," the advice states.
The HSE has said that it is monitoring the ongoing situation closely.