Another seven cases of unexplained hepatitis in children are under investigation, according to the Health Service Executive.
This is in addition to the six cases confirmed by the HSE last week; one child has died of the mystery illness and one had required a liver transplant.
Disclosing the extra cases under investigation, HSE chief clinical officer Dr Colm Henry described the recent discovery of hepatitis cases of unknown origin among children as a cause for concern, but added that cases were thankfully rare.
Dr Henry told the Oireachtas health committee on Wednesday that work was underway at European level to try to find a cause. One suggestion is it could be linked to a reaction to an adenovirus - a common virus that affects children.
The six previously confirmed Irish cases were aged between one and 12 years of age. All were hospitalised.
Cases of unexplained hepatitis have risen to at least 429 in 22 countries, the World Health Organisation (WHO) said this week.
The number of countries reporting at least five cases has doubled since the last WHO briefing in April, from six to 12. Nine of these are in Europe.
A further 40 possible cases of acute liver disease are awaiting classification, officials told a press conference in Geneva on Tuesday.
Six children have died and 26 have required transplants, according to Prof Philippa Easterbrook of the WHO's global hepatitis programme. About 75 per cent of cases are in children aged under five years.