Washington (AFP) - US authorities are scrambling to get to the bottom of a rash of deaths of US tourists in the Dominican Republic, with the number of reported fatalities over the past year now rising to six.

Three people whose deaths have been confirmed all arrived on May 25 in San Pedro de Macoris, a seaside resort in the south of the Caribbean country, Dominican authorities said.

Miranda Schaup-Werner, 41, booked a room with her husband at the Luxury Bahia Principe Bouganville hotel. She lost consciousness on the day of her arrival after going out on the balcony. She could not be revived by her husband or hotel medical staff.

Cynthia Day, 49, and Edward Holmes, 63, stayed in an adjacent hotel, Grand Bahia Principe La Romana. The couple from Maryland was found dead on May 30 in their room by hotel staff.

According to the Dominican Prosecutor's Office, the three victims died of respiratory failure and pulmonary edema. Schaup-Werner also had a heart attack.

- A pattern? -

News of the deaths has drawn attention to earlier deaths of American tourists at island resorts that received no publicity at the time -- some now suspect -- may have been part of a pattern.

The sister of Yvette Monique Short told a Philadelphia television station that the 51-year-old died last June at the Bahia Principe after having a drink from the minibar in her room.

Two other deaths that have recently come to light occurred more than a year apart at the Hard Rock Hotel and Casino in the resort town of Punta Cana.

Robert Wallace, a 67-year-old from California, died there April 14, after drinking a Scotch from his minibar and falling ill, his niece Chloe Arnold told Fox News.

"He started feeling very sick, he had blood in his urine and stool right afterward," she said.

David Harrison, 45, had died at the same hotel in July 2018. His widow, Dawn McCoy, initially accepted that he succumbed to a heart attack, as she was told, but now questions it.

"When all these people started passing, I stopped and thought to myself, 'How can all these people have the same cause of death as David?' " she told The Washington Post.

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Steven Bullock, a lawyer for Day's family, said autopsies and tests will be performed on Day and Holmes in the US.

Asked about contacts with Dominican police and authorities, Bullock said "it has been very, very difficult. We haven't heard enough and that's part of the problem.

"We don't seem to be getting anything (from police). We have some reporters on the ground that are assisting us in gathering information that might be available," he told AFP.

Meanwhile, Colorado couple Kaylynn Knull and Tom Schwander told CNN that they suffered from headaches, abdominal cramps and diarrhea after encountering a strong smell of chemicals in the La Romana hotel in June 2018.

According to tests done on their return home, they could have been exposed to pesticides used against ants and cockroaches.

The couple, who lodged a complaint, believes that the product has spread through the air conditioning system.