Table 1

Description of measures of influenza-related illness during initial epidemic of pdmH1N1
Measure Description Period analyzed No. at-risk/samples tested No. of episodes/positive tests
Pri Sec Pri Sec
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 25 Jun 2009 to 10 Oct 2009 (weeks 25 to 40)1 NA NA 440 279
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 21 Jun 2009 to 10 Oct 2009 (weeks 25 to 40)2 1,372 1,029 878 656
Sch-LCC: Lab confirmed cases of pdmH1N1 Notifications of laboratory confirmed cases of pdmH1N1 as compiled by the Ministry of Education 12 Jun 2009 to 7 Oct 2009 (weeks 23 to 40) 270,3443 215,3793 654 533
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 30 Jun 2009 to 24 Jul 2009 (weeks 26 to 29)4 270,3443 215,3793 4,656 2,932
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 29 Jun 2009 to 3 Oct 2009 (weeks 26 to 39)5 4,320 4,821 964 1,178
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 Pre-SS: 1 Feb 2008 to 31 May 2009 381 321 3 34
Post-SS: 1 Oct 2009 to 2 Jun 2010 124 96 41 39

1 Estimates for epidemiological week 25 were extrapolated from the ILI rate for the 3 days (25 June to 27 June 2009) where data was available.

2 Only data from these dates were extracted, though surveillance extends before and after these dates.

3 Based on school enrolment on 29 June 2009.

4 Data on 29 June 2009 discarded due to inaccuracies in reporting on first day of school.

5 Up to week 34 for all 6 schools, and up to week 39 for 2 primary and 2 secondary schools.

Soh et al.

Soh et al. BMC Infectious Diseases 2012 12:336   doi:10.1186/1471-2334-12-336

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