Some 33 people were struck down with norovirus in Ireland this week, according to the HSE.
Noroviruses are one of the most common causes of gastroenteritis or stomach bugs. Symptoms include nausea, vomiting, and diarrhoea, and some people may have a raised temperature, chills, muscle aches and headaches.
The HSE told Independent.ie today that the first week of 2019 saw 31 individual cases of norovirus, and one separate outbreak which included two cases of the bug.
"This compares with three outbreaks of norovirus during the same period last year, resulting in 110 people ill," a spokesperson for the HSE said.
"Currently norovirus notification activity is about normal," the spokesperson said.
There were 19 cases during Christmas week, and 24 cases in the penultimate week of 2018.
Around the world, certain areas have noted a spike in norovirus activity at the end of 2018, the HSE said.
"This is not uncommon over the Christmas period, as people tend to remain indoors, and visit family and friends, which facilitates spread of norovirus," the spokesperson added.
Symptoms begin around 12 to 48 hours after becoming infected. The illness is usually brief, with symptoms lasting only about one or two days. Most people make a full recovery within one to two days, however some people, usually the very young or elderly, may become very dehydrated and require hospital treatment.
Noroviruses are very contagious and can spread easily from person to person.