Attack rates and viral types of identified outbreaks.

#Type A: Old dormitory style; Type B: modern single-level purpose built facility with adjacent independent living unit; Type C: modern single-level purpose built facility. Analysed using exact Wilcoxon test. +Analysed using Poisson regression. †Analysed using negative binomial regression. 1Late in the outbreak, the local public health unit started prophylaxis with oseltamivir for the remaining residents.