Acute Gastroenteritis Outbreak Among Colorado River Rafters and Backpackers in the Grand Canyon, 2022

Area of Science:

• Epidemiology
• Infectious Diseases
• Public Health

Background:

• An increase in acute gastroenteritis reports occurred in Grand Canyon National Park between April and May 2022.
• Norovirus genogroups I and II were identified in portable toilet specimens, indicating a potential outbreak.

Purpose of the Study:

• To investigate transmission contributors and individual risk factors for acute gastroenteritis among individuals rafting or backpacking in Grand Canyon National Park.
• To understand the dynamics of the norovirus outbreak during the specified period.

Main Methods:

• An online survey was administered to Grand Canyon rafters and backpackers from June 13 to July 8, 2022.
• A Cox proportional hazards model was employed to identify predictors of illness, adjusting for confounding factors.

Main Results:

• Out of 762 surveys, 119 cases and 505 well individuals provided complete data.
• Illness in rafters correlated with contact with sick individuals (adjHR=3.4) and insufficient hand hygiene before snacks (using only sanitizer/water: adjHR=1.6).
• Younger age groups (<40 and 40-59 years) exhibited higher illness rates compared to those aged 60 and above.

Conclusions:

• Person-to-person transmission is the probable cause of the widespread norovirus outbreak.
• Recommendations for future outbreak mitigation include pre-trip symptom screening, immediate isolation of ill individuals, rigorous handwashing with soap and water, reduced social interactions, and enhanced public health notices.