a<p>Number in parenthesis refers to sample determined to be positive by qRT-PCR without documented seroconversion or single positive HI titer.</p>b<p>Symptomatic infections include those having positive respiratory sample for A(H1N1)pdm09 by qRT-PCR or ≥4-fold increase in HI titer of paired ILI sera or single positive HI titer with ILI or respiratory illness within 7 days prior to study enrollment.</p>c<p>Subclinical infections include those having ≥4-fold increase in HI titer of paired ILI sera or single positive HI titer without ILI or respiratory illness within 7 days prior to study enrollment.</p><p>Age distribution of contact subjects with laboratory-confirmed A(H1N1)pdm09 infection, Kamphaeng Phet, Thailand.</p
