The UK has reported an unusual cluster of heart inflammation in newborn babies caused by catching enterovirus, the World Health Organisation (WHO) has said.

Myocarditis, or inflammation of the heart muscle, was the presenting feature, and cases peaked in November 2022, with sporadic cases reported across the other months. Enterovirus infections are typically mild, but they can be more severe in newborns than in older children.

In early April, the UK notified the WHO about an increase in severe myocarditis in infants in Wales. A total of 15 cases consistent with neonatal sepsis in babies 28 days old and younger were reported from Wales and southwest England from June 2022 and March 2023.

Polymerase chain reaction (PCR) testing in nine patients confirmed either coxsackie B3 or coxsackie B4. As of April, three patients were hospitalised, four were receiving outpatient care, and two died.

The WHO said though infections from enterovirus are common in young babies, the link to myocarditis with severe outcomes in the group is "unusual".

"The reported incident represents an increase in both the number and severity of enterovirus infections in infants under the age of one month," the WHO said. Only one case had been identified in Wales in the six years prior to 2022.

According to Professor Paul Hunter, an expert in medicine at the University of Anglia, there was no cause for concern.

"The big problem with these types of cluster is knowing whether this represents a real change or a random clustering with little long term importance," he was quoted as saying to the Telegraph. "Most but not all apparent clusters do not go on to pose a consequential threat to public health.

"Nevertheless, you cannot afford to assume that they will not progress and you have to investigate them."

An incident management team is reviewing all the evidence and has alerted UK authorities, who have raised awareness among health providers about the enterovirus cluster. Epidemiologic investigations are still under way. (PB/NewsGram)