Mexican triplets have tested positive for coronavirus at birth and are believed to have contacted the virus in the utero.

The children, two boys and one girl, were born by cesarean section last Wednesday in the state of San Luis Potosi, in north-eastern Mexico.

“On the same day they were born, they were tested because they were premature, and the results were positive,” the state’s health secretary, Monica Rangel said at a press conference on Monday.

The children’s results arrived on Saturday.

Only one has shown symptoms of COVID-19, but the other two are asymptomatic, as were their parents who are still awaiting the results of their own tests.

According to Rangel, it would be “impossible” for them to have caught the disease after they were born, as they were tested within hours of their birth.

“Here what we will have to investigate is a situation, perhaps, where (the virus) has been transmitted through the placenta. It is not something that we confirm,” she added.

“The case is striking, we are going to study it.”

Coronavirus is spreading rapidly in Mexico.

Photo above is a stock image.

This article originally appeared on Over60.