Two American citizens were found dead Tuesday in a hotel room in Mexico, a US State Department spokesperson said.
They have been identified as 28-year-old Abby Lutz and her boyfriend, 41-year-old John Heathco, by Lutz's stepsister, Gabrielle Slate.
The couple was discovered in the Mexican resort village of El Pescadero in Baja California Sur state, a statement from the state attorney general's office said.
Slate told CNN she talked to her stepsister earlier this week during the couple's vacation and said Lutz and Heathco thought they had gotten food poisoning.
"They had been sick for a few days. She had gone to the hospital to get an IV and came back to the hotel feeling good," Slate said, adding that "they had a day of enjoying their trip and doing well and then we were notified yesterday of their passings."
An autopsy determined the cause of death was poisoning "by a substance to be determined without traces of violence in the body," the attorney general's office said.
Authorities were called Tuesday night to the hotel in the Todos Santos district, where they discovered the couple's bodies.
"We offer our sincerest condolences to the families on their loss, the US State Department spokesperson said. "We are closely monitoring local authorities' investigation into the cause of death."
The FBI is not currently involved in the investigation, a US law enforcement source familiar with the incident told CNN, noting that at this point there is no indication of foul play.
The pair had been dead for approximately 10 to 11 hours, authorities said.
"No evidence of violence or alteration of the scene was found at the location," the attorney general's office said.
Henar Gil, the general manager of the Rancho Pescadero hotel, said they are "heartbroken" but are unaware of any threats to guests.
"We are truly heartbroken by this terrible tragedy. Our hearts are with the impacted families and loved ones during this unimaginable loss," Gil said in a statement provided to CNN by Hyatt Hotels Corporation. "Local authorities are still actively investigating the situation, and the safety and security of our guests and colleagues remains a top priority, as always."
"We can confirm there was no evidence of violence related to this situation, and we are not aware of any threat to guests' safety or wellbeing," Gil added. "We are working to care for those who have been impacted and we are working closely with authorities as they conduct their investigation to understand the cause of death."
"We just want everyone just to know how much we love her," Slate told CNN. "We're gonna miss her. And we're sad that it happened the way it did."
Slate has organized a GoFundMe for transportation and funeral costs that has raised more than $9,900.
CNN's Alisha Ebrahimji, Colin McCullough, Josh Campbell, Tina Burnside and Chris Boyette contributed to this report.
