Widespread outbreak of norovirus gastroenteritis among evacuees of Hurricane Katrina residing in a large "megashelter" in Houston, Texas: lessons learned for prevention.

Background: After Hurricane Katrina, an estimated 200,000 persons were evacuated to the Houston metropolitan area, >27,000 of whom were housed in 1 large "megashelter," the Reliant Park Complex. We investigated an outbreak of gastroenteritis reported among the evacuees who resided in the Reliant Park Complex to assess the spread of the infectious agent, norovirus, and to implement and evaluate the effectiveness of interventions used for control.

Methods: Public health authorities conducted surveillance of gastroenteritis among evacuees treated at the Reliant Park Medical Clinic during 2-12 September 2005. Basic demographic and clinical data were recorded. Specimens of stool and vomitus were collected and tested for bacteria, parasites, and viruses. Shelter census data were used to estimate the daily incidence of disease.

Results: During a period of 11 days, >1000 patients were treated at the clinic for gastroenteritis, which accounted for 17% of all clinic visits. Norovirus was the sole enteric pathogen identified, but multiple different strains were involved. Among the evacuees residing in the Reliant Park Complex, the incidence of gastroenteritis was estimated to be 4.6 visits per 1000 persons per day, and among the evacuees who resided there for 9 days, 1 (4%) of 24 persons would have been ill. Intensive public health measures were promptly instituted but did not definitively slow the progression of the outbreak of norovirus gastroenteritis.

Conclusions: Our investigation underscores the difficulties in managing such outbreaks in crowded settings and the need for rapid, sensitive laboratory assays to detect norovirus. Additional research is needed to establish more effective measures to control and prevent this highly contagious gastrointestinal illness.