Grand Canyon Boaters Illness Identified

Grand Canyon National Park
June 20, 2002

Preliminary evidence of a gastrointestinal illness reported by persons participating in recent rafting trips on the Colorado River in Grand Canyon National Park indicates a Norwalk-like virus has caused the outbreak. The first illness was reported to have started on June 1 and the last case on June 14. During that time 51 people are thought to have suffered from diarrhea and vomiting with a 1-2 day duration. This number has changed from previous reports as cases are reviewed. It now appears that at least one hiker may be included among those who have contracted the illness. One of the difficulties in tabulating an exact number of cases is that the symptoms are very similar to those identified with heat-related conditions that are also common at this time of the year. Two medical evacuations were conducted for people suffering from symptoms similar to this illness, but at the time of evacuation they were thought to be suffering from dehydration.

Analysis of a single specimen obtained from a portable toilet used by one of the river groups confirmed a virus. Additional specimens from other affected river groups, and individuals who have suffered from the illness are being analyzed. Results from these additional specimens are anticipated early next week. Norwalk-like viruses are the most common cause of gastrointestinal illness in the United States and are among the most common outbreaks of vomiting and diarrhea. The virus can be easily spread through person to person contact or inadequate sanitation practices. The National Park Service (NPS) and the Centers for Disease Control and Prevention in Atlanta, Georgia will be conducting a number of additional studies. An epidemiology study comparing individuals who became sick with individuals on the river during the same time period who remained healthy is currently underway. Environmental sampling is also being conducted. A river trip is scheduled for the purposes of sampling numerous sites along the river corridor to determine if there are any point sources of the virus. Results from this study are expected later this summer.

River users are reminded to be extra vigilant with their sanitation practices. Drinking water obtained from the river or side canyons should be filtered and treated with iodine or chlorine, then allowed to rest before consumption. An alternative method is to boil all drinking water. Frequent hand washing and careful food preparation helps to control the spread of the illness from person to person. River guides who develop the illness while on a trip should not participate in food preparation.

A number of people and agencies have cooperated in researching and minimizing the spread of this illness. River guides were prompt in reporting when it became obvious that this involved more than a few isolated cases. This rapid reporting system was developed in response to similar illnesses in 1994 and 2000. Others assisting the NPS, include the United States Public Health Service, Centers for Disease Control and Prevention, Coconino County Department of Public Health, and the Department of Health Services.