title: Norovirus Outbreaks Among Colorado River Rafters in the Grand Canyon, Summer 2012.
abstract: OBJECTIVE
  To investigate the incidence and causative agent of the recurrent outbreaks of acute gastrointestinal illness (AGI) among different rafting groups on the Colorado River in the Grand Canyon National Park during the 2012 summer season.
  
  
  METHODS
  Confidential illness reports were completed by all individuals with symptoms of AGI, and samples of fecal matter and vomitus, surface swabs of rafting equipment, and environmental swabs at stops along the hiking corridor were collected and tested for the presence of norovirus using reverse transcription-quantitative polymerase chain reaction (RT-qPCR).
  
  
  RESULTS
  During the active outbreak period between May 9 and July 9, 2012, 97 rafters (1.4%) from 10 trips (2.9% of all trips) declared AGI symptoms. AGI incidence within the 10 infected trips varied from 6% to 88%. Outbreaks occurred in 3 distinct temporal clusters that involved 2 different genogroups of norovirus. All available toilet fecal samples (5 samples) were positive for norovirus RNA: 1 with genogroup I (GI) and 4 with GII. The vomitus sample tested positive for GI. None of the fomite samples from rafting equipment or from the hiking corridors were confirmed for norovirus.
  
  
  CONCLUSIONS
  The results suggest that norovirus may have been introduced by ill or asymptomatic individuals actively shedding the virus in their vomitus or feces, and spread within, or between, river trips by different modes of transmission. This study reinforces the importance of appropriate guidance and practice regarding norovirus prevention and the necessity of postoutbreak containment in relatively isolated groups of individuals.
authors.affiliation: Midwestern University, Physician Assistant Program, Glendale, AZ (Ms Magill-Collins and Dr Stoehr). Electronic address: jstoehr@midwestern.edu.
authors.forename: Anne
authors.initials: A
authors.lastname: Magill-Collins
authors.affiliation: Coconino County Health District, Environmental Health Division, Flagstaff, AZ (Ms Gaither).
authors.forename: Marlene
authors.initials: M
authors.lastname: Gaither
authors.affiliation: Department of Soil, Water and Environmental Science, The University of Arizona, Tucson, AZ (Drs Gerba, Kitajima, and Iker).
authors.forename: Charles P
authors.initials: CP
authors.lastname: Gerba
authors.affiliation: Department of Soil, Water and Environmental Science, The University of Arizona, Tucson, AZ (Drs Gerba, Kitajima, and Iker); Center for Environmental Sensing and Modeling, Singapore-MIT Alliance for Research and Technology, Singapore (Dr Kitajima).
authors.forename: Masaaki
authors.initials: M
authors.lastname: Kitajima
authors.affiliation: Department of Soil, Water and Environmental Science, The University of Arizona, Tucson, AZ (Drs Gerba, Kitajima, and Iker).
authors.forename: Brandon C
authors.initials: BC
authors.lastname: Iker
authors.affiliation: Midwestern University, Physician Assistant Program, Glendale, AZ (Ms Magill-Collins and Dr Stoehr).
authors.forename: James D
authors.initials: JD
authors.lastname: Stoehr
mesh_terms: D000293:Adolescent; D000328:Adult; D001130:Arizona / Q000453:epidemiology; D017250:Caliciviridae Infections / Q000453:epidemiology* / Q000821:virology; D004196:Disease Outbreaks; D004783:Environmental Microbiology; D005759:Gastroenteritis / Q000453:epidemiology* / Q000821:virology; D006801:Humans; D015994:Incidence; D008875:Middle Aged; D029322:Norovirus / Q000302:isolation & purification*; D012189:Retrospective Studies; D020133:Reverse Transcriptase Polymerase Chain Reaction; D045483:Rivers; D012767:Ships; D013177:Sports; D055815:Young Adult
keywords: Grand Canyon; gastroenteritis; norovirus; outbreak