Multistate Cryptosporidiosis Outbreak Associated with a Virginia Campground, 2015

BACKGROUND: In July 2015, the Virginia Department of Health received a report that approximately 40 persons developed gastrointestinal illness after a reunion event at a Virginia campground; this event involved 500 attendees from multiple states. Information gathered from attendees implicated campground pools as the exposure source. Furthermore, pool quality complaints had been received from campers not associated with the reunion in the weeks prior to the event. In collaboration with other state health departments and the Centers for Disease Control and Prevention (CDC), an investigation was initiated to determine the causative agent, identify additional cases, ascertain risk factors associated with infection, and prevent further illness.

METHODS: The investigation initially focused on the reunion event, but expanded to include all recent campground visits due to the suspected involvement of the campground pools. Campground management provided a list of registered campers and an electronic survey was distributed to collect demographic, clinical, and exposure information. Stool samples collected from ill persons were tested for parasites by enzyme-linked immunosorbent assay or direct fluorescent antibody at commercial and public health laboratories. Five human samples were sent to the CDC microbiology laboratory for molecular typing. The local health department conducted a campground inspection and detailed assessments of the pools. Distribution system and raw well water samples were tested for total coliforms and Escherichia coli. Education and outreach were provided to affected persons and the campground.  

RESULTS: Surveys revealed multiple fecal accidents occurred in campground swimming pools prior to the outbreak. Multiple pool water quality issues were noted during inspections, including improper chlorination, the presence of algae, and high water turbidity. In total, 87 gastrointestinal illnesses were reported among campground guests, with the leading risk factor identified to be swallowing any pool water (RR = 2.4; p-value < 0.001). Eight human specimens were positive for Cryptosporidium; four were typed as Cryptosporidium hominis IfA12G1. Initially, distribution system and raw well water samples were positive for total coliforms and raw well water was also positive for E. coli. All subsequent water samples were negative for both total coliforms and E. coli. Campground pools were closed, partially drained, refilled, and properly chlorinated before being reopened to the public.

CONCLUSIONS: Cryptosporidium is highly resistant to chlorine, and routine chlorination of contaminated water does not destroy oocysts. Proper fecal accident response procedures are critical for maintaining safe waters. Swallowing water during swimming and swimming in waters that appear abnormal should be avoided.