Norovirus GII.P16-GII.4 Sydney outbreak among wildfire evacuation shelter populations — Butte County, California, November 2018

  • Water or foodborne
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Background:
On November 8, 2018, Camp Fire, California’s largest wildfire to date, displaced ~52,000 persons, with >1,100 evacuated to 9 shelters in Butte and surrounding counties. Before the fire, norovirus GII.P16 GII.4 Sydney was reported in the community. On November 10, 2 evacuees from 2 shelters experienced acute gastrointestinal illness (AGI). To identify AGI cases and prevent transmission, Butte County Public Health Department (BCPHD) initiated shelter surveillance and assessed on-site infection prevention and control (IPC), assisted by the California Department of Public Health.

Methods:
On November 10, BCPHD distributed paper logs to shelter staff to enter information on persons with AGI (vomiting or diarrhea). When feasible, symptomatic persons submitted stool specimens. We defined confirmed cases as AGI among shelter staff/evacuees with a norovirus-positive stool specimen detected by real-time reverse– transcription polymerase chain reaction; norovirus-positive specimens were genotyped. Probable cases were AGI among staff/evacuees without associated specimens. We analyzed demographics, AGI trends, and assessed IPC.

Results:
During November 10–December 1, 292 cases (16 confirmed, 276 probable) were identified among a fluctuating population of ~1100 people across 8 shelters (attack rate ~27%). Twenty-one of 292 cases (7%) sought hospital evaluation and 12 (4%) were staff. Of 255 patients with data, median age was 63 years (interquartile range 52-71). Sixteen (94%) of 17 available specimens were positive for norovirus GII.P16-GII.4 Sydney. The outbreak peaked on November 14 with 54 new cases. On-site assessment revealed deficiencies in surveillance, isolation, cleaning services, and handwashing. In response, we established illness screening at registration, isolation protocols, 24-hour on-site cleaning, and handwashing champions. By December 1, there were no incident cases.

Conclusion:
Mass sheltering, limited surveillance, and suboptimal IPC likely facilitated norovirus transmission after Camp Fire. Disaster relief balances numerous competing urgencies; however, prioritizing effective shelter surveillance and IPC is necessary to proactively identify and contain outbreaks.

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