Figure. Nine annual cycles (unbroken lines) of general practitioner (A) and general outpatient clinic (B) geographic sentinel surveillance data from Hong Kong Island, Kowloon, New Territories East, and New Territories West, 1998–2007. The monthly proportions of laboratory samples testing positive for influenza isolates are overlaid as gray bars, and the beginning of each annual period of peak activity (inferred from the laboratory data) is marked with a vertical dotted line. ILI, influenza-like illness.
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