Figure 1From: Assessing secondary attack rates among household contacts at the beginning of the influenza A (H1N1) pandemic in Ontario, Canada, April-June 2009: A prospective, observational study Distribution of time from symptom onset of primary case to symptom onset of secondary case. Note: Co-primary cases are included. Date of onset was unknown for 8 secondary cases. ARI, acute respiratory illness. ILI, influenza-like illness.Back to article page