The four Americans who were shot at and abducted in Mexico were reportedly visiting for medical tourism — making them part of a booming industry that is vital to Mexico's economy.

"Pre-pandemic, some 1.2 million American citizens traveled to Mexico for elective medical treatment," Josef Woodman, CEO of Patients Beyond Borders, told NPR. His firm publishes a guide to international medical travel.

Here's an update on medical tourism, and the recent tragedy:

U.S. medical travel is rising sharply

"Today, the market is recovering rapidly in Mexico, nearly back to its pre-pandemic levels," Woodman said.

Nearly 780,000 people were projected to leave the U.S. for health care in 2022, according to Healthcare.com, citing data from the medical travel website Medical Departures.

That outburst of activity got a big boost in late 2021, when the U.S. relaxed key border restrictions with Mexico.

Costa Rica is the second-most popular destination for U.S. visitors seeking medical care elsewhere, Woodman said. It's a particular draw, he added, for people in the Northeast and Southeast.

Most people travel for dental and cosmetic work

Cosmetic surgeries are just one of the procedures that are far cheaper in Mexico — for years, people have been visiting from the U.S. to get elaborate dental work or cosmetic treatments done, or to pick up antibiotics and other medicines at favorable prices.

Many people also travel to get orthopedic work done, replacing knees or hips for less than half the cost of such procedures in the U.S.

"North American patients travel to Mexico for care primarily to save 50-70% over what they would pay in the United States for an elective treatment," according to Woodman.

Medical tourism does bring risks, experts say

While an element of risk is inherent in many procedures no matter where they're performed, medical tourism can heighten complications, according to the Centers for Disease Control and Prevention.

Potential problems range from the dangers of flying in a pressurized plane cabin too soon after a surgery to the complications of getting follow-up care for a procedure done in another country.

Some of the most serious warnings from the CDC are for infections, from wound and blood infections to pathogens that might be more common or resistant in the host country than in the U.S.

"Recent examples include surgical site infections caused by nontuberculous mycobacteria in patients who underwent cosmetic surgery in the Dominican Republic," the CDC says, "and Q fever in patients who received fetal sheep cell injections in Germany."

U.S. medical tourists rate Mexico highly

A 2020 research paper that surveyed some 427 Americans crossing the U.S.-Mexico border in California for medical services found that most of the respondents "felt that Mexican health care services are of the same or better quality compared with those in the United States, for a lower cost."

People had come from 29 states across the U.S. to get care in Mexico, with the vast majority driven by cost concerns, according to the paper, published in the Journal of the American Pharmacists Association.

The researchers also collected data about the medical tourists themselves, reporting an average age of 64.5 years. Their most common yearly income range was reported to be between $25,001 and $50,000 — but that reflects less than a quarter of the respondents.

More than 400 of the survey's 427 participants said they would undertake more medical tourism in the future, the paper said.

Most of Mexico's hospitals follow U.S. standards

Mexico has worked for years to promote medical tourism to draw patients across the U.S. border. That includes improving its health system and following international standards.

"About 10 years ago, the Mexican federal government licensed the Joint Commission accreditation standards, which are used to accredit U.S. hospitals," as David Vequist, who runs the Center of Medical Tourism Research at the University of the Incarnate Word in San Antonio, told NPR's All Things Considered.

"So most Mexican hospitals are now basically using the same standards we use in hospitals in the United States," Vequist added.

Details of the recent violence are still emerging

At least one of the U.S. citizens who were caught up in the recent tragedy was reportedly going to Mexico for a tummy tuck operation. But the group's vehicle came under fire hours after entering the border city of Matamoros, Mexico, from Brownsville, Texas.

Two of the four died; all are reported to be natives of Lake City, S.C. Their identities have not been released, but relatives have been speaking to NPR and other outlets.

Mexican officials say they believe the four were caught in the middle of a conflict between drug cartels in the state of Tamaulipas — an area that is under a do-not-travel advisory from the U.S. State Department.