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

Delphine Pessoa,Kari Auranen,Fabian Hoti,Ritva Syrjänen,Raquel Sá-Leão,Tarja Kaijalainen,M Gabriela M Gomes

doi:10.1186/1471-2334-13-180

Abstract

BackgroundDay-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.MethodsLongitudinal 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.ResultsThe 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.ConclusionsThe 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.

Highlights

Day-care centre (DCC) attendees play a central role in maintaining the circulation of Streptococcus pneumoniae in the population
Let Tir;s denote the set of times the carriage status changes from state r to state s in the time interval ]tmin, tmax], where tmin is one day before the first nasopharyngeal sample and tmax is the day after the Let lTaist1⁄4nÈaTsoirp;sh:arr;ysng1⁄4ea1l; sampleÉ . . . ; ns is taken in the dataset. be the collection of all times child i changes carriage status
Among the 254 positive samples from the Portuguese DCC, 14 serotypes were identified, whereas 20 serotypes were identified among the 138 isolates from the Finnish DCCs

Summary

Introduction

Day-care centre (DCC) attendees play a central role in maintaining the circulation of Streptococcus pneumoniae (pneumococcus) in the population. We compared key parameters underlying pneumococcal transmission in DCCs to understand which of these contributed to the observed differences in carriage prevalence. Streptococcus pneumoniae (pneumococcus) is one of the most important bacterial causes of respiratory tract infections worldwide [1]. While it can cause serious illnesses, pneumococcus carriage in its ecological niche, the human nasopharynx, is generally asymptomatic. Erästö et al [7] estimated serotype-specific parameters simultaneously in Bangladeshi families and concluded that, while more common serotypes in the study area were more often acquired from the community, these differences loose significance when conditioning on exposure within the family. Lipsitch et al [9], focusing on the competitive ability of specific serotypes in Kenya, reported significant differences in susceptibility to competition, which appears positively correlated with the rate of clearance

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