Table 1 Description of measures of influenza-related illness during initial epidemic of pdmH1N1

GP-ILI: No. of ILIs per GP doctor

Based on ILI reporting by network of 23 GPs, where numerator is number of ILI reports and denominator is number of GPs reporting per day (median 14/d, IQR: 10-15); ILI is defined here as a consult for acute respiratory illness with a temperature of 38°C and above

Lab-ILI: Proportion of ILIs at GP clinics testing positive for pdmH1N1

Based on testing of ILI samples from a separate sentinel GP network by the National Public Health Laboratory, where numerator is number of samples positive for pdmH1N1 and denominator is number of samples tested; ILI is defined here as a consult for acute respiratory illness with a temperature of 38°C and above

Sch-LCC: Lab confirmed cases of pdmH1N1

Notifications of laboratory confirmed cases of pdmH1N1 as compiled by the Ministry of Education

Sch-DTM: Daily tempe-rature moni-toring

Temperature taking of students conducted twice daily in all schools; counts of the number of students detected to have fever on twice daily temperature taking is presented, with fever defined as 37.9°C and above for children of ages 12 years and below and 37.6°C and above for children of ages 13 years and above

Sch-FRI: Febrile respiratory illness reporting

3 primary and 3 secondary schools from different areas of Singapore were selected to report FRI episodes, with FRI defined as fever of ≥ 37.5°C accompanied by either cough or sore throat; data was collated by the class teacher-in-charge once every 2 weeks

Pre-SS and Post-SS: Pre-epidemic and post-epidemic serological surveys

Age-stratified serological data based on the proportion with hemagglutination inhibition titers ≥ 40 to pdmH1N1 in post-epidemic samples (Post-SS) minus that in pre-epidemic samples (Pre-SS), adjusted for the sensitivity of detecting confirmed infections using cross-sectional hemagglutination inhibition titers ≥ 40 to pdmH1N1