It was a vacation nightmare. A Wilmington family of four staying in a Virgin Islands condo, with idyllic views of Cruz Bay on St. John, suddenly became seriously ill. So ill that they were airlifted home and hospitalized, the father and two teenage boys in critical condition.

The likely scenario that has emerged is that they were poisoned after methyl bromide was sprayed in the condo underneath the one where the family was staying. The pesticide is banned in many countries and is not authorized for use in residences in the U.S.

The incident, while deemed uncommon, has heightened concerns about travelers' exposure to pesticides in other regions or countries that may not have usage restrictions or regulatory oversight as stringent as that in the U.S.

"Can this go on as you travel around the world? It's easy to misuse a pesticide. It's easier in a country where there's a language difference and a lack of oversight or enforcement," said Jay Feldman, executive director of the national nonprofit advocacy group Beyond Pesticides, based in Washington.

"In many developing counties where there is a protracted man vs. insect battle, lots of misapplications take place," said Mark Robson, a professor in Rutgers University's School of Environmental and Plant Sciences. He also edits the Journal of Human and Ecological Risk Assessment. "One should be cautious, avoid the applications when possible, and assume they will occur in developing countries."

Paramedics in the Virgin Islands responded to a call March 20 at the Sirenusa Condominium Resort. The four people sickened were Stephen Esmond, an administrator at the private Tatnall School in Wilmington; his wife, Theresa Devine, a dentist; and their teenage sons Sean and Ryan, both students at Tatnall. The family's spokesman, Wilmington attorney James J. Maron, later said that the Esmonds were "in good hands medically" at undisclosed locations and that their conditions were improving.

Meanwhile, the U.S. Environmental Protection Agency, which has jurisdiction because St. John is a U.S. territory, continues to work with the Virgin Islands government and others to determine precisely what happened, a spokesman said. EPA regional administrator Judith Enck said in a prepared statement that her agency would "make sure steps are taken to prevent this from happening to others at these vacation apartments or elsewhere."

The family's symptoms have not been described. However, a fact sheet issued by the National Pesticide Information Center, a cooperative effort between Oregon State University and the EPA, indicates that methyl bromide is "highly toxic." Symptoms of exposure include headache, nausea, vomiting, visual disturbances, malaise, confusion, loss of coordination, slurred speech, and irritation of the skin, eyes, and respiratory system. Severe poisonings can result in paralysis, convulsions, coma, and death, according to the center. It said signs of poisoning might appear right away, or up to 48 hours after exposure.

Pesticide exposure is more commonly a concern for farm workers who apply them. "The life-threatening experience that this family experienced is an extreme version of what farm workers are exposed to routinely," said Jennifer Sass, senior scientist and toxicology expert at the Natural Resources Defense Council, a national nonprofit advocacy group.

The council has been advocating for a ban on the use of methyl bromide in the U.S., because of its extreme toxicity and because it depletes the protective ozone layer in the upper atmosphere. By continuing to allow even restricted uses in the U.S., Sass said, "you're also allowing people to buy it, sell it, and possess it."

The EPA has identified Terminix as the company that applied the chemical. "If a company as large as Terminix, which has trained workers presumably, are using pesticides in what appears to be unlawful ways . . . then how many other small companies are doing it that have less of a reputation?" she said. "I don't think we know."

Beyond Pesticides' Feldman said his office frequently received calls from vacationers to the Caribbean, Mexico, and other warm-climate areas who worry they might have been exposed to toxic pesticides. A typical scenario is a vacationer noticing a vehicle driving through the resort, emitting a noxious fog.

A news search brings up a smattering of results, not a public-health epidemic.

Nevertheless, in March, a Quebec coroner concluded that two sisters who were found dead in 2012 in their hotel room in Thailand most likely were poisoned by phosphine, a chemical used to exterminate bedbugs, according to a report in the Montreal Gazette.

Another bedbug pesticide, pyrophus, has been implicated in the deaths of a California woman and six other tourists in a different hotel in Thailand, according to a 2011 report in Britain's Daily Mail.

The crowd-sourced travel booking and review site TripAdvisor.com has numerous comments from vacationers who noticed a fog of what was presumably an insecticide at their resort.

"The grounds staff drive a golf cart around the resort roughly twice per day spewing a pesticide fog from a machine on the back," said one woman of a resort in the Turks and Caicos.

Robson said he has been sprayed as he sat by the pool at a resort in Africa, in airplanes, and even one time in a sauna in Poland. "Many places have unqualified people making these applications, typically in long white coats and wearing gloves and goggles, while you sit there by the pool in only a bathing suit."

The continuing spread of insect-borne diseases such as chickungunya, and nuisance pests such as bedbugs, may be exacerbating the problem, Feldman said. "Especially when there are insects that carry diseases that represent a public-health problem, there's a tendency to turn to more highly toxic chemicals and to use them more broadly."

He suspects that many vacationers are exposed to low doses of pesticides, but never realize it. The headache, nausea, and dizziness attributed to overindulgences may actually be a reaction to a chemical.

Feldman advises those with concerns to check with the hotel or resort management ahead of time to ask what chemicals are used. He also suggests that when travelers arrive, they open the doors and windows to their rooms to air them out.