Figure 1.

Sample selection. A total of 135 serum samples were tested; 58 sera were from individuals with febrile respiratory illness (FRI), 29 of whom tested positive by reverse transcription polymerase chain reaction (RT-PCR) for influenza A/H3N2. Of these H3N2⁺ cases, 25 were negative for other respiratory pathogens, while 4 were also positive for rhinovirus (Rhino⁺). Another 29 sera were from individuals with FRI who tested negative for influenza A/H3N2 by RT-PCR. Of these H3N2⁻ individuals, 16 were negative for all other respiratory pathogens and 13 were Rhino⁺. The H3N2⁻ (n = 29) and housing (n = 77) individuals were used as the control group (n = 106).