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“There is an old saying: Travel expands the mind and loosens the bowels,” says Davidson Hamer. That is certainly true for college students, who are three times more likely to study abroad now than 20 years ago—and for them, acute diarrhea is the most common illness resulting from their travels.

Many students returning from abroad have infections besides acute diarrhea that can be prevented with vaccination or other methods, this even though a majority of them had pretravel health consultations, according to a new study coauthored by Hamer, a School of Public Health professor of global health, and published in the Journal of Travel Medicine.

“We found that easily preventable infections occurred in some student travelers,” he says, “including malaria, which can be prevented by effective antimalarial chemoprophylaxis, hepatitis A, and typhoid fever—for which we have good vaccines for prevention.”

For the study, Hamer and his colleagues used data from 432 student travelers who returned to the United States from abroad with an illness and received a confirmed diagnosis at a US GeoSentinel site from 2007 to 2017. The GeoSentinel Global Surveillance Network is a collaboration initiated in 1995 between the International Society of Travel Medicine and the Centers for Disease Control and Prevention (CDC). It now consists of 72 specialized travel and tropical medicine clinical sites in 31 countries around the world. Hamer is the principal investigator for GeoSentinel.

Among the 432 students, there were 581 confirmed diagnoses. Almost half of them were gastrointestinal, and acute diarrhea accounted for 43 percent of those diagnoses. Exposures occurred in 69 countries, the overwhelming majority (81 percent) classified by the World Bank as low- or middle-income countries. The most common regions of exposure were sub-Saharan Africa, followed by South America and Central America; the top-five exposure countries were India (11 percent), Ecuador (7 percent), Ghana (6 percent), China (6 percent), and Peru (5 percent).

The researchers found that 7 percent of the students had vector-borne diseases, with malaria accounting for 41 percent of them and dengue fever accounting for 32 percent. Three students, or 13 percent, had vaccine-preventable diseases: two were typhoid and one was hepatitis.

Two of the students had acute HIV infections, which Hamer says is “a very worrying finding. The risk of this disease and the need for safe sexual practices should be emphasized.”

The study found 70 percent of the students had had pretravel health consultations, which, the authors wrote, is a much higher rate than that seen among tourists or people traveling to visit friends and family. “However, this means that 30 percent did not,” Hamer says. “For international travel, especially if travel is planned to a low- or middle-income country, a consultation with a travel medicine specialist to review potential risks and how to prevent infections is highly recommended.”

“Both study abroad programs and healthcare providers should emphasize location-specific disease risks, particularly for diseases with a high prevalence in the area or diseases with high morbidity or mortality, such as malaria,” the authors report.

Kristina Angelo of the CDC Division of Global Migration and Quarantine is the study’s lead author. Among the other coauthors is Boston Medical Center pediatrician Elizabeth Barnett (MED’85), a School of Medicine professor of pediatrics.

Michelle Samuels can be reached at