'Stuck in a nightmare,' says relative of Texas couple who mysteriously died in Fiji

A mystery illness that killed a Texas couple on a dream vacation to Fiji continued to baffle doctors Wednesday as authorities in the South Pacific island nation said they have ruled out one possible cause for their demise -- influenza.

David Paul, 37, and his wife, Michelle Paul, 35, died two days apart after coming down with a violent illness that caused vomiting, diarrhea, hand numbness and shortness of breath, their relatives said.

"I'm stuck in a nightmare," Rebecca Ward, the sister of David Paul, said in an interview on ABC's "Good Morning America" on Wednesday. "You think you're going to have an answer today and you get a call that they don't know."

The Health Ministry in Fiji said an investigation into the causes of death is ongoing and that they still have no definitive answers on what killed the seemingly healthy couple.

"Influenza has been ruled out, and at this stage, we do not believe there is a risk to the public," the Fiji Ministry of Health said in a statement released Tuesday night. "It would be premature to speculate further on the cause of death until the investigation is complete."

A small number of people, including health workers who came in close contact with the couple, are being monitored as a precaution. They are all "currently well," the Health Ministry's statement reads.

The U.S. Centers for Disease Control and Prevention and the World Health Organization are assisting in the investigation.

Michelle Paul's father, Marc Calanog of Las Vegas, told ABC News that autopsies on the couple have been completed in Fiji and specimens from post mortem examination are being sent to the CDC's headquarters in Atlanta to be analyzed.

David and Michelle Paul arrived in the South Pacific archipelago of more than 300 islands on May 22 and checked into the Sheraton Denarau Villas.

"After reporting feeling unwell, the guests were treated at the local medical facility, where they subsequently passed away," the resort said in a statement. "Our thoughts and prayers are with the family and loved ones of the deceased. As always, the well-being of our guests and associates remains our highest priority. We are working closely with the authorities as they investigate the matter."

Michelle Paul died on May 25 after telling her father in a WhatsApp text that both she and her husband had contracted a violent illness and that both of them had symptoms of vomiting, diarrhea and profound weakness. Calanog said his daughter also complained of numbness in her hands.

Dr. Jennifer Ashton, ABC News chief medical correspondent, said on GMA Wednesday that authorities may have to wait for toxicological reports to come back before they get any definitive answers on why their illnesses to took a deadly twist.

"I spoke to a top infectious disease specialist ... who said there is almost no infection that out of the blue can kill two healthy people this quickly," Ashton said. "So, again, their symptoms may be a clue. We need a post mortem autopsy and toxicology because when you see two people young and healthy die suddenly, that is really, really suspicious."

Rebecca Ward said the couple had been in contact with family members during their health crisis.

She said the couple was taken to a clinic but released and went back to their hotel to try to get rest.

"And then when my brother woke up, Michelle was just clammy and sweating and he was too weak to take her to the hospital himself," Ward said on GMA.

She said that when the couple returned to the hospital it was too late for Michelle Paul.

"They couldn't get her an IV, couldn't revive her, and that's when she passed away," Ward said. "Not long after that, my brother ended up at the hotel, then later on that day he went back to the hospital. He got released again and we thought he would be able to come home."

She said her brother messaged their mother on Facebook saying he was OK.

"We were hoping to see him in the next few days. Then the next thing we hear he was back in the hospital with shortness of breath and that was the last time we actually talked to him," she said.

Rebecca Ward said her brother and sister-in-law are survived by four young children, a 1-year-old boy they had together, and three children from previous relationships who are now in the custody of relatives in the United States.

"Nobody thinks that two healthy people will go on this nice vacation and then all of the family back home is left with questions and trying to figure out even what the next step to move on is," she said. "It puts life ... in perspective, definitely."