Last week, four Americans were kidnapped in Mexico. One of the four, Latavia Washington McGee, crossed the border for a scheduled cosmetic surgery, according to CNN. It’s a growing trend known as medical tourism, and while it’s already a multibillion-dollar market, it’s proving to be problematic. Two of the abducted travelers were found dead and two were found alive near the border city of Matamoros. Investigators are still putting the pieces together to determine what happened to the four Americans.

“It’s on the daily, without a doubt,” Dr. Nolan Perez, a gastroenterologist in Brownsville, Texas, told CNN. “There are people going daily to get this kind of stuff done. Whether it’s primary care provider visits or dental procedures or something more significant, like elective or weight loss surgery, there’s no doubt that people are doing that because of low cost and easier access.”

According to the Centers for Disease Control and Prevention, millions of U.S. residents travel internationally for medical care each year — an ongoing trend that comes with a warning.

“Ongoing reports of infections and other adverse events following medical or dental procedures abroad serve as reminders that medical tourism is not without risks,” the CDC warned.

“People travel because there may be a long waiting time, wait lists or other reasons why they can’t get treatment as quickly as they would like it,” Elizabeth Ziemba, president of Medical Tourism Training, told CNN. “So they explore their options outside the United States to see what’s available.

“Price is a big issue in the United States. We know that the US health care system is incredibly expensive. Even for people with insurance, there may be high deductibles or out-of-pocket costs that are not covered by insurance, so that people will look based on price for what’s available in other destinations.”

The CDC warned that the procedure and destination both need to be considered before a U.S. resident makes any major medical-related traveling decisions.

“Common categories of procedures that US medical tourists pursue include dental care, noncosmetic surgery (such as orthopedic surgery), cosmetic surgery, fertility treatments, organ and tissue transplantation, and cancer treatment,” the CDC reported. “Medical tourism destinations for US residents include Argentina, Brazil, Costa Rica, Cuba, India, Malaysia, Mexico, Singapore, and Thailand. When reviewing the risks associated with medical tourism, travelers should consider both the procedure and destination.”