A 12-day-old girl died after contracting the common cold sore virus in hospital days after birth.
Eibhlín Wills acquired the infection in the first five days of her life, an inquest into her death heard.
Blood tests showed no sign of the infection three days after birth but the infection was present in samples taken when Eibhlín was five days old.
Dublin Coroner Dr Myra Cullinane found the infant died due to a hospital-acquired infection.
The family described the loss of their precious baby as an "unspeakable horror".
"For the past three years we have had to live with the unspeakable horror of losing our baby girl to an entirely preventable disease.
"While it has been extremely painful to go through the details again ... today's verdict gives us the opportunity to again warn the public and especially the families of newborns and those caring for them, of the potential danger of the common cold sore virus," Eibhlín's father, John Wills said.
The coroner recommended that the Minister for Health include neonatal herpes as a formally notifiable disease and endorsed and commended the Wills family's efforts to raise awareness of the dangers of neonatal herpes.
Parents John and Louise Wills, from Rathfarnham in Dublin, welcomed baby Eibhlín, their first-born, into the world on 19 November 2015.
She was born at the National Maternity Hospital in Holles Street where she was cared for until her discharge on 24 November.
"She was a babbly, amenable baby," said Mr Wills. "She was this tiny little person who was incredibly alert for her age."
He told Dublin Coroner's Court how the couple cared for their newborn after bringing her home.
"We spent those first few days getting used to her. She was feeding well and sleeping well and settled into her little routine," he said.
The public health nurse visited the family on 27 November.
"The nurse was very happy with her. That weekend Eibhlín seemed to have picked up a cold. She was sniffling a little but she was still feeding," Mr Wills said.
By Monday, the infant was feeding less and she seemed tired. John and Louise phoned the hospital and were told to bring the baby in if they remained concerned. They called Louise's mother who arrived at their home at 11.30pm.
"Very suddenly Eibhlín went limp and her colour changed. We drove her straight to Tallaght Hospital," Mr Wills said.
Resuscitation attempts failed and the baby was pronounced dead at 1.09am on 1 December.
A post-mortem conducted by Dr Michael McDermott gave the cause of death as disseminated neonatal herpes simplex virus type 1, the virus that causes the common cold sore.
Dr McDermott found no other abnormalities or underlying vulnerabilities other than the infant's age.
"This was an overwhelming primary infection and it was a recent infection," Dr McDermott said.
The court heard details of ongoing training to prevent cross-contamination at the National Maternity Hospital. Staff with a visible cold sore are expected to cover it with a patch.
Obstetrician Prof Mary Higgins said baby Eibhlín was a "a beautiful little girl who left us far too soon".
She said the infant's death from the virus had an impact on the hospital staff.
"When you are looking after a person who is sick you have to be so careful not to pass it onto another person. Basic principals of hand hygiene are integrated into training as a student and again at induction days.
"Infection control staff give talks on hand hygiene and universal precautions. Before you approach someone you wash your hands so as not to pass on any bacteria," she said.
Virologist Professor Cillian De Gascun performed laboratory tests on blood samples provided by the hospital following the autopsy.
"The challenge with herpes is you can actually transmit the virus without having a cold sore. In a significant proportion of cases, there won't be a cold sore and it's passed on as it is asymptomatic."
Asked if the virus is more likely to be spread when a cold sore is present, Prof De Gascun said it was.
Coroner Dr Myra Cullinane returned a verdict of death due to a healthcare-acquired infection and commended the couple on their efforts to raise awareness of the dangers of the HSV virus.
"I endorse the ongoing raising of awareness of this condition for the public and other maternity hospitals in order this can be prevented as much as possible, although it is never possible to entirely eliminate tragedies such as this.
"This is such an affecting inquest, you have been very active in the raising awareness and have to be commended on what you've done," the coroner said.
The Department of Health has said it is working on new regulations to make neonatal herpes a notifiable disease before the end of this year.
In a statement, it said: "The department is currently in the process of finalising the text of the Infectious Diseases (Amendment) Regulations 2018 with the Office of the Parliamentary Counsel and the HSE. Under the provisions of this regulation, neonatal herpes will be included amongst the list of notifiable diseases. It is intended that the regulations will be finalised and signed into law before the end of this year".
Eibhlín's parents John and Louise Wills have been engaging with the department on the issue.
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