Here's what we know so far.
News of the mass illness comes as another tourist has died in the Hispaniola island nation, bringing the total number of Americans to die mysteriously there to eight this year.
The deaths have continued occurring, with three taking place in June after three happened in late May. He died hours later.
The State Department confirms that there have been at least 8 deaths of Americans in the Dominican Republic since last June, but most of the deaths are concentrated near the Punta Cana area of the island. Family members told WKYC in OH that 78-year-old Jerry Curran, a retiree who lived in Florida, died in January after falling ill on the island.
Sport got a drink from the mini bar in her hotel room before going to bed and never waking up, her family said.
One person told NBC News that she lost 19 pounds, saying that she was "just grateful to be alive at this point".
California man Robert Bell Wallace, 67, died on 14 April after getting sick at the Hard Rock Hotel & Casino in Punta Cana. According to the hotel, Schaup-Werner's husband said she had had a heart condition.
His family didn't return phone calls or emails from Fox News. Prescription drugs, including blood pressure medication and five-milligram doses of the painkiller oxycodone, were found in the room that Day and Holmes had been staying in.
He tested negative for salmonella, but others in the group have tested positive, he said.
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"Our plan was to spend our honeymoon at the resort and instead we left a day early", Massaranduba said.
"I just woke up, and my stomach was cramping and I was sweating", Hill told KOCO-TV.
The couple is in the process of suing the hotel to determine what chemicals they might have been exposed to during their trip, and as more Americans continue to get sick and die at the hotel, Schwander and Knull's story has found new life.
And in June 2018, Yvette Monique Sport died at the Bahia Principe in Punta Cana, her sister, Felecia Nieves, told CNN. He was found dead the next day during a wellness check. Hurlbut Sr.'s cause of death was officially listed as a heart attack, although his son is now suspicious.
Schaup-Werner suffered from a heart attack, pulmonary edema, and respiratory failure, according to a preliminary autopsy cited by the Attorney General's Office of the Dominican Republic.
The Federal Bureau of Investigation (FBI) Headquarters in Washington on January 7, 2019.
The couple also had fluid in their lungs, Attorney General Jean Alain Rodriguez Sanchez's office said in a statement. The U.S. Department of State and our embassies and consulates abroad have no greater responsibility than the protection of U.S. citizens overseas.
A similar unexplained death the previous week, that of 53-year-old Leyla Cox, has been described as "an isolated incident" by the republic's Tourism Minister Francisco Javier Garcia. "The wide availability of weapons, the use and trade of illicit drugs, and a weak criminal justice system contribute to the high level of criminality on the broader scale".
He said that the grounds supervisor at the hotel also recognized the smell in their room as the same substance being sprayed on the flowers. David Ortiz, the retired Boston Red Sox player, was shot and wounded June 9 in Santo Domingo. "They didn't have any answers for us, so we didn't feel safe staying at the resort".
Experts have urged travelers not to avoid the country, arguing that a handful of cases shouldn't taint the entire destination.
The FBI and U.S. Centers for Disease Control and Prevention have joined the effort to pinpoint the cause of the string of deaths, which has been speculated to be bootleg liquor or poisoning. Those deaths were caused by drowning, accidents, suicide and homicide. The investigations into the deaths have included visits from health inspectors, including environmental health and epidemiology specialists, according to Carlos Suero, spokesman for the Ministry of Public Health.