Figure 2

Empirical Estimate of Cumulative Specimens Tested for One or More Positive Test Results in Documented Norovirus Gastroenteritis Outbreaks. Specimens are numbered in the order in which they were accessioned by the laboratory. Solid line represents outbreaks without confirmation by electron microscopy; dashed line represents outbreaks identified by real-time reverse-transcriptase polymerase chain reaction (RT²-PCR) alone.