ST. JOHN, Virgin Islands, April 4 (UPI) -- The U.S. Environmental Protection Agency on Friday said exposure to a pesticide with restricted use in the United States may have caused severe illness in a Delaware family vacationing at a Virgin Islands resort.

Steve Esmond, his wife and two teenage sons had been renting a villa at the Sirenusa resort on St. John in the U.S. Virgin Islands since March 14. The EPA received reports of the family falling ill on March 20; paramedics had found Esmond unconscious and his wife and sons, 14 and 16, having seizures.

According to family attorney James Maron, Esmond is still unable to move or talk, and his two sons are in critical condition after being airlifted to the United States, where on Saturday they remained in a coma at a Philadelphia hospital. Esmond's wife, Theresa Devine, was released after treatment but remains in occupational therapy.

Speaking Friday, EPA spokesman Elias Rodriguez said preliminary tests did "show that there was a presence of methyl bromide in the unit where the family was staying."

The EPA defines methyl bromide as a "broad spectrum pesticide" designed to control "pest insects, nematodes, weeds, pathogens, and rodents," but that it "will affect not only the target pests it is used against, but non-target organisms as well."

"Human exposure to high concentrations of methyl bromide can result in central nervous system and respiratory system failure, as well as specific and severe deleterious actions on the lungs, eyes, and skin," according to the agency.

Because of its toxicity, methyl bromide is only permitted for outdoor use by certified professionals in the United States.

Sirenusa resort was reportedly fumigated on March 18, and the EPA is working with local investigators to discern whether any laws or regulations were breached.

Sea Glass Vacations, the rental agency for several villas at Sirenusa resort, said it uses an outside pest control company called Terminix.

"We're thinking about the family, and we join the community in wishing them a speedy recovery," Terminix wrote in an email statement to CNN, noting also that it is "looking into this matter internally, and cooperating with authorities."

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EPA: Pesticide may have caused illness in family staying at Virgin Islands resort