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Open Access Research article

Comparative analysis of Streptococcus pneumoniae transmission in Portuguese and Finnish day-care centres

Delphine Pessoa1, Fabian Hoti23, Ritva Syrjänen2, Raquel Sá-Leão4, Tarja Kaijalainen2, M Gabriela M Gomes15 and Kari Auranen2*

Author Affiliations

1 Instituto Gulbenkian de Ciência, Oeiras, P-2781-901, Portugal

2 Department of Vaccination and Immune Protection, National Institute for Health and Welfare (THL), Helsinki, Finland

3 Department of Information and Computer Science, Aalto University School of Science, Espoo, Finland

4 Laboratory of Molecular Microbiology of Human Pathogens, Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa (ITQB/UNL), Oeiras, Portugal

5 Programa de Computação Científica, Fundação Oswaldo Cruz, Rio de Janeiro, 21045-900, Brazil

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BMC Infectious Diseases 2013, 13:180  doi:10.1186/1471-2334-13-180

Published: 18 April 2013

Abstract

Background

Day-care centre (DCC) attendees play a central role in maintaining the circulation of Streptococcus pneumoniae (pneumococcus) in the population. The prevalence of pneumococcal carriage is highest in DCC attendees but varies across countries and is found to be consistently lower in Finland than in Portugal. We compared key parameters underlying pneumococcal transmission in DCCs to understand which of these contributed to the observed differences in carriage prevalence.

Methods

Longitudinal data about serotype-specific carriage in DCC attendees in Portugal (47 children in three rooms; mean age 2 years; range 1–3 years) and Finland (91 children in seven rooms; mean age 4 years; range 1–7 years) were analysed with a continuous-time event history model in a Bayesian framework. The monthly rates of within-room transmission, community acquisition and clearing carriage were estimated.

Results

The posterior mean of within-room transmission rate was 1.05 per month (Portugal) vs. 0.63 per month (Finland). The smaller rate of clearance in Portugal (0.57 vs. 0.73 per month) is in accordance with the children being younger. The overall community rate of acquisition was larger in the Portuguese setting (0.25 vs. 0.11 per month), in agreement with that the groups belonged to a larger DCC. The model adequately predicted the observed levels of carriage prevalence and longitudinal patterns in carriage acquisition and clearance.

Conclusions

The difference in prevalence of carriage (61% in Portuguese vs. 26% among Finnish DCC attendees) was assigned to the longer duration of carriage in younger attendees and a significantly higher rate of within-room transmission and community acquisition in the Portuguese setting.

Keywords:
Streptococcus pneumoniae; Pneumococcus; Day care; Child; Transmission; Carriage; Prevalence; Longitudinal studies; Portugal; Finland; Statistical models; Bayesian inference; Data augmentation