PCR and Culture Analysis of Streptococcus pneumoniae Nasopharyngeal Carriage in Healthy Children.

Leah J Ricketson,Otto G Vanderkooi,James D Kellner,Ravinder Lidder,Robyn Thorington,Irene Martin,Manish Sadarangani

doi:10.3390/microorganisms9102116

Abstract

Invasive Streptococcus pneumoniae disease is preceded by asymptomatic nasopharyngeal carriage. Measuring carriage in healthy populations provides data on what serotypes are present in communities, which is of interest in the era of polyvalent pneumococcal conjugate vaccines. Nasopharyngeal swabs from a survey of 682 and 800 healthy children in 2016 and 2018, respectively, were analyzed by culture and Quellung reaction to determine rates of carriage and serotypes. All swabs from 2016 and 300 randomly selected swabs from 2018 were then analyzed using real-time semi-quantitative PCR (qPCR) to detect S. pneumoniae gene targets lytA, piaA, and SP2020 and determine serotype. There were 71 (10.4%) and 68 (8.5%) culture positive samples in 2016 and 2018, respectively. All of these were also positive by qPCR except one that was equivocal. In total, 46.0% of 2016 swabs were positive by qPCR. In 2018, results from the selected sample extrapolated to the complete sample showed 49.0% positive by qPCR. PCV13 serotypes were detected in 29.3% and 21.7% of S. pneumoniae qPCR positive samples from 2016 and 2018, respectively; compared with only 8.4% and 6.0% PCV13 serotypes detected by Quellung reaction in culture positive samples. Compared with culture, qPCR detected S. pneumoniae more frequently. Further, qPCR serotyping detected PCV13 serotypes in a larger proportion of samples than culture and Quellung reaction did, showing that, despite established universal childhood PCV13 immunization, vaccine serotypes can still be detected in a large proportion of young children.

Highlights

Streptococcus pneumoniae is an opportunistic pathogen because it colonizes asymptomatically, with carriage being a prerequisite for disease [1,2]
Used towas indicate reaction thatResults could not serotyped of
We found that qPCR detected S. pneumoniae more frequently than conventional culture in nasopharyngeal samples obtained from healthy children, long after the introduction of

Summary

Introduction

Streptococcus pneumoniae (pneumococcus) is an opportunistic pathogen because it colonizes asymptomatically, with carriage being a prerequisite for disease [1,2]. Especially in children, can act as an important reservoir that facilitates horizontal spread of. S. pneumoniae throughout a community [1]. The seven-valent pneumococcal conjugate vaccine (PCV7) targets seven serotypes (4, 6B, 9V, 14, 18C, 19F, and 23F) and was introduced in the province of Alberta, Canada in 2002 with three doses given before a year of age and a single booster after one year (3 + 1 schedule) [3]. In 2010, Alberta introduced the thirteen-valent pneumococcal conjugate vaccine (PCV13) with a 2 + 1 schedule, which added serotypes 1, 3, 5, 6A, 7F, and 19A to the serotypes already included in the PCV7 vaccine [3].

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