Another American has died in the Dominican Republic, bringing the total to at least nine this year and four this month. Khalid Adkins, 46, of Denver, Colorado, died Tuesday, according to the New York Daily News.

A State Department spokesperson confirmed to CBS News that a U.S. citizen died in the Dominican Republic on June 25. The cause of his death has not been disclosed.

Colorado station KDVR-TV first reported Adkins’ condition Tuesday night, when he was forced to disembark from a scheduled plane ride home because he was too ill to fly. His sister-in-law, Marla Strick, told KDVR-TV that he vomited in the plane’s bathroom and was hospitalized in Santo Domingo, where she was told “his kidneys were failing.” His daughter Mia Adkins wrote on her Facebook page that her father “got super sick” after visiting the Dominican Republic with her last week.

After Adkins was taken off the plane he “spent the past three days there in critical condition – vomiting, alone and screaming in pain in a hospital bed,” his relatives told the New York Post.

Adkins’ family told the Daily News they are not sure what caused his death and that his body is undergoing an autopsy in the Dominican Republic.

This is the fourth death this month of an American visiting the Dominican Republic. Vittorio Caruso died June 17, Joseph Allen died on June 13 and Leyla Cox died on June 10. Unlike Cox and Allen, Caruso had been splitting time between the U.S and Dominican Republic for nine years.

The deaths of the Americans reportedly occurred after they complained of feeling ill after eating a meal or drinking out of hotel minibars. The U.S. embassy in Santo Domingo said there is no proof the deaths are linked.

Last week, CBS News spoke with C├ęsar Duvernay, a spokesperson for the Dominican Republic’s foreign ministry, who said the cases are isolated out of more than 6 million tourists, and that this doesn’t mean the country is unsafe. He noted that the government has a special body focused on tourism safety, with protocols in place that have not changed.

Several of the deaths were reported to be heart attacks, which health officials said is the most common cause of death for Americans on vacation.