A Filipino woman and her American husband died last month from an unidentified illness during their holiday in Fiji.

On May 22, the couple, David Paul and his wife Michelle, who lived in Texas, arrived in Nadi, Fiji, on vacation. A few days later, the couple fell ill and suffered from diarrhea, vomiting and numbness. According to the couple’s relatives, both were physically fit before they went to Fiji, Philippine Daily Inquirer reported.

Fiji’s Ministry of Health and Medical Services said the couple’s condition worsened despite receiving medical treatment at a hospital. Michelle died first and David passed away while waiting for further treatment.

The ministry said it was working with police forensics, the World Health Organization and the US Centers for Disease Control and Prevention to try to determine what caused their deaths. The couple’s remains cannot be returned to the US until a cause of death is determined.

The US Embassy in Fiji said it had been working with the Fiji government, police and health officials for more than a week to investigate their deaths.

“We appreciate the efforts made thus far by the Fijian authorities and stand ready to provide further assistance, if requested. At this point, we are not aware of any specific public health threat to the community,” an embassy statement said.

The couple left behind a two-year-old son and David’s daughter from a previous relationship.