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. 2011 Feb 23;6(2):e17074.
doi: 10.1371/journal.pone.0017074.

Age-specific incidence of A/H1N1 2009 influenza infection in England from sequential antibody prevalence data using likelihood-based estimation

Marc Baguelin  1 , Katja Hoschler, Elaine Stanford, Pauline Waight, Pia Hardelid, Nick Andrews, Elizabeth Miller
Affiliations

Age-specific incidence of A/H1N1 2009 influenza infection in England from sequential antibody prevalence data using likelihood-based estimation

Marc Baguelin et al. PLoS One. .

Abstract

Estimating the age-specific incidence of an emerging pathogen is essential for understanding its severity and transmission dynamics. This paper describes a statistical method that uses likelihoods to estimate incidence from sequential serological data. The method requires information on seroconversion intervals and allows integration of information on the temporal distribution of cases from clinical surveillance. Among a family of candidate incidences, a likelihood function is derived by reconstructing the change in seroprevalence from seroconversion following infection and comparing it with the observed sequence of positivity among the samples. This method is applied to derive the cumulative and weekly incidence of A/H1N1 pandemic influenza in England during the second wave using sera taken between September 2009 and February 2010 in four age groups (1-4, 5-14, 15-24, 25-44 years). The highest cumulative incidence was in 5-14 year olds (59%, 95% credible interval (CI): 52%, 68%) followed by 1-4 year olds (49%, 95% CI: 38%, 61%), rates 20 and 40 times higher respectively than estimated from clinical surveillance. The method provides a more accurate and continuous measure of incidence than achieved by comparing prevalence in samples grouped by time period.

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Conflict of interest statement

Competing Interests: KH: In 2006 Sanofi Pasteur paid conference fees and accommodations for an international meeting at which he presented data for a Sanofi vaccine study. ES has received support to attend a scientific meeting from Wyeth Vaccines in 2006. The RVU lab (KH) has received funding for influenza vaccine work from Novartis, Sanofi Pasteur, Baxter and CSL Australia. This does not alter the authors' adherence to all the PLoS ONE policies on sharing data and materials. The other authors (MB, PW, PH, NA, EM) have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Proportion of clinial cases by week.
Proportion of clinical cases by week for the second wave for four age-groups (1–4, 5–14, 15–24, 25–44 years) derived from clinical surveillance data.
Figure 2
Figure 2. Estimation of the interval to seroconversion.
a) Proportion of individuals with HI titer <32 by interval since symptom onset: blue lines and points show the proportion in four-day intervals with confidence intervals and the red curve show the fitted parametric inverse cumulative distributions with the 95% CI (credible intervals) and b) distribution of the time to seroconversion since symptoms with 95% CI.
Figure 3
Figure 3. Posterior distribution of the cumulated incidences.
Estimated cumulated incidence distributions for age-groups 1–4, 5–14, 15–24, 25–44 years during the second wave.
Figure 4
Figure 4. Changes in seroprevalence and cumulative incidence over time.
Estimated changes in seroprevalence and cumulative incidence compared with proportion with HI titer ≥32 by week by age group a) 1–4 years, b) 5–14 years c) 15–24 years d) 25–44 years.
See this image and copyright information in PMC

References

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