Preliminary autopsies released by Dominican authorities said they all had fluid in their lungs and respiratory failure. The FBI is conducting toxicology reports on those three deaths.
The series of fatalities are causing concern among Americans thinking of coming to the island. According to the State Department, 13 Americans died there all of last year and three were considered homicides.
In a statement, the U.S. ambassador to the Dominican Republic said, "The safety and security of U.S. citizens that live in, work in, and visit the Dominican Republic remains our highest priority. These incidents are tragic and we offer our deepest condolences to those personally impacted."
(WATCH: More Oklahomans Report Illness After Trip To Dominican Republic)