Norovirus found to cause traveler's diarrhea

A majority of traveler’s diarrhea cases among U.S. travelers to Mexico and Guatemala were attributed to Norovirus, a common cause of nonbacterial gastroenteritis outbreaks usually associated with developed countries, according to a new study by researchers at the Johns Hopkins Bloomberg School of Public Health and other institutions.

The researchers also found that the longer travelers stayed at their destination, the more likely they were to contract Norovirus infections. The study is published in the March 2005 issue of the Journal of Clinical Microbiology.

“Noroviruses are known to be a major cause of food and waterborne gastroenteritis outbreaks in domestic and unique settings, such as cruise ships, and also have been documented among military groups during deployment overseas. However, few studies have investigated the prevalence of Norovirus infection among civilians traveling from industrialized to developing countries,” said Kellogg J. Schwab, PhD, corresponding author of the study and an assistant professor in the Department of Environmental Health Sciences at the Johns Hopkins Bloomberg School of Public Health.

He explained that Noroviruses often are not considered in studies of traveler’s diarrhea because, until recently, molecular detection methods for these viruses have not been readily available in laboratories in the United States or other countries.

The researchers examined stool samples from 34 individuals who experienced traveler’s diarrhea during trips to Antigua, Guatemala or Cuernavaca, Mexico, for Noroviruses, as well as for bacterial and protozoan pathogens. Sixty-five percent of the individuals in the study had at least one stool sample positive for Norovirus. Although Norovirus previously has been implicated as a cause of traveler’s diarrhea among visitors to Mexico, this is the first study to indicate that Norovirus contributes to traveler’s diarrhea in visitors to Guatemala.

Amy R. Chapin, first author of the study and a PhD-candidate in the Department of Environmental Health Sciences at the Johns Hopkins Bloomberg School of Public Health, noted that 11 Norovirus-positive stool samples also were positive for E. coli, a leading bacterial cause of traveler’s diarrhea, thus indicating that dual infections among individuals experiencing traveler’s diarrhea may be more common than previously thought.

The authors said that further research into the role of Noroviruses in traveler’s diarrhea is warranted. The simple, inexpensive molecular diagnostic techniques used in this study to identify Norovirus-positive stool samples could serve to facilitate future Norovirus-related research in developing countries.

“Prevalence of Norovirus among U.S. Visitors to Mexico and Guatemala Experiencing Traveler’s Diarrhea” was supported by a grant from the Center for a Livable Future at the Johns Hopkins Bloomberg School of Public Health. Amy R. Chapin was also supported by a Howard Hughes Medical Institute Predoctoral Fellowship in Biological Sciences.