Figure 1: Epidemic curve of seasonal influenza A and pandemic H1N1 influenza at a large pediatric hospital in Toronto, Canada. Specimens originated from inpatients, outpatients and patients seen in the emergency department. Pandemic H1N1 polymerase chain reaction (PCR) testing was introduced on Apr. 28, 2009. Some cases of influenza A detected by means of direct fluorescent antibody assay (DFA) or viral culture before this date may have been pandemic H1N1 influenza.