Synoptic view of CoPanFlu protocol implementation.

<p>Green and violet lines represent the number of blood samples collected from the cohort, on inclusion (weeks 30–44) and at the end of the study (weeks 45–52) respectively (Y axis at the left: number of samples collected). Shaded area represents the profile of the epidemic wave in Reunion Island according to the local epidemiology surveillance unit (Y axis at the right: estimated number of symptomatic influenza cases occurring in the island); X axis: calendar weeks.</p

The cohort profile and major outcomes.

<p><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0025738#pone-0025738-g001" target="_blank">Figure 1</a> details the three phases of the protocol: i) inclusion (weeks 30–44) and serum samples S1 collection; ii) follow up for detection of ILI in households, qRT-PCR on nasal swabs and estimation of cumulative seroincidence rates; iii) end of the study (weeks 45–52) and samples S2 collection. HIA on paired sera (S1+S2) allowed estimating seroconversion rates.</p

Probability of seroconversion according to age and to baseline pre-epidemic HIA titer.

<p>Probability of seroconversion according to age and to baseline pre-epidemic HIA titer.</p

Socio-demographic and space-time characteristics of the COPanFlu-RUN cohort subjects compared to the community, Reunion Island, 2009.

<p>Data are numbers (percentages);</p><p>*paired sera;</p><p>**French National Institute for Statistics and Economical Studies (INSEE) source.</p

Seroconversion rates according to age and baseline-proxy HIA titers in 249 individuals enrolled in pre-pandemic phase, CoPanFlu-RUN cohort, Reunion Island, 2009.

<p>Data are numbers, percentages (100 * number seroconverters/number tested (95% confidence intervals)) and ALR parameter test <i>P</i> value for comparison of seroconversion proportions between baseline-proxy HIA titer (<1/40 versus ≥1/40), in each age, after controlling for household selection. In the group “All ages” seroconversion rates were standardized according to age structure of the community.</p><p>*HIA titer: hemagglutination inhibition assay titer. Seroconversion was defined as a shift from seronegative at inclusion (i.e. HIA titer <1/40) to seropositive on follow-up sample, or as a 4-fold increase of reciprocal HIA titer between first and second paired samples for sera tested seropositive on inclusion (i.e. HIA titer ≥1/40).</p

Seroconversion rates to 2009 pandemic influenza A H1N1 virus (pH1N1/2009) according to age and time of first sample (S1) collection, CoPanFlu-RUN cohort, Reunion Island, 2009.

<p>Data are numbers, percentages (95% confidence intervals) and ALR parameter test <i>P</i> value for comparison of seroconversion proportions according to time of first sample (S1) collection at inclusion, in each age group, after controlling for household selection. In the group “All ages”, rates of seroconversion were standardized according to age structure of the community. NA: not assessed. Seroconversion was defined as a shift from seronegative at inclusion (i.e. HIA titer <1/40) to seropositive on follow-up sample, or as a 4-fold increase of reciprocal HIA titer between first and second paired samples for sera tested seropositive on inclusion (i.e. HIA titer ≥1/40). W30–31: first sample collected in early epidemic phase (baseline-proxy); W32–39: first sample collected during the full development of the epidemic wave; W40–44: first sample collected in the immediate post- epidemic phase; W30–44: whole inclusion period.</p