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Density Distribution of Pharyngeal Carriage of Meningococcus in Healthy Young Adults: New Approaches to Studying the Epidemiology of Colonization and Vaccine Indirect Effects

Finn, Adam PhD; Morales-Aza, Begonia BSc; Sikora, Paulina BSc; Giles, Jessica BSc; Lethem, Ryan BSc; Marlais, Matko MD; Thors, Valtyr MD; Pollard, Andrew J. PhD; Faust, Saul PhD; Heath, Paul MD; Vipond, Ian PhD; Ferreira, Muriel MD; Muir, Peter PhD; Januário, Luís MD; Rodrigues, Fernanda PhD

The Pediatric Infectious Disease Journal: October 2016 - Volume 35 - Issue 10 - p 1080–1085
doi: 10.1097/INF.0000000000001237
Original Studies
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Background: Improved understanding of Neisseria meningitidis (Nm) carriage biology and better methods for detection and quantification would facilitate studies of potential impact of new vaccines on colonization and transmission in adolescents.

Methods: We performed plate cultures on 107 oropharyngeal swabs stored frozen in skim milk tryptone glucose glycerol (STGG) broth and previously positive for Nm. We compared quantitative polymerase chain reaction (qPCR) detection of Nm in 601 STGG-swabs with culture. Using qPCR (n = 87), a log-phase broth culture standard curve and semiquantitative plate cultures (n = 68), we measured density of carriage. We compared qPCR genogrouping of DNA extracts from STGG-swabs and from plate culture lawns (n = 110) with purified isolates (n = 80).

Results: Swab storage resulted in only 10% loss of culture sensitivity. Direct sodC qPCR Nm detection yielded more positives (87/601, 14.5%) than culture (80/601, 13.3%). Most samples (57/110) positive by culture were also positive by qPCR and vice versa, but discrepancies (single positives) were frequent among low-density samples. sodC qPCR was positive in 79/80 isolates but in only 65 by ctrA qPCR. Density both by culture and qPCR varied across 4 orders of magnitude with the majority being low (<50 bacteria-gene copies/mL) and a minority being high (>1000). Genogrouping qPCRs yielded more positive results when performed on DNA extracts from lawn cultures.

Conclusions: We provide the first description of the distribution of Nm carriage density. This could be important for understanding transmission dynamics and population-level effectiveness of adolescent vaccine programs. Storage of swabs frozen in STGG for batched laboratory analysis facilitates carriage studies and direct sodC qPCR for Nm combined with qPCR genogrouping of lawn culture extracts provides accurate, detailed description of colonization.

From the *Bristol Children’s Vaccine Centre, School of Cellular and Molecular Medicine, University of Bristol, Bristol, United Kingdom; Oxford Vaccine Group, Department of Paediatrics, University of Oxford and the NIHR Oxford, Biomedical Research Centre, Oxford, United Kingdom; Academic Unit of Clinical and Experimental Sciences, Faculty of Medicine and Institute for Life Sciences, University of Southampton, Southampton, United Kingdom; §Southampton NIHR Wellcome Trust Clinical Research Facility, University Hospital Southampton NHS Foundation Trust, Southampton, United Kingdom; Vaccine Institute & Paediatric Infectious Diseases Research Group, Division of Clinical Sciences, St. George’s, University of London, London, United Kingdom; Public Health Laboratory Bristol, Public Health England, Bristol, United Kingdom; **Infectious Diseases Unit and Emergency Service, Hospital Pediátrico, Centro Hospitalar e Universitário de Coimbra, Coimbra, Portugal; and ††Faculty of Medicine, Universidade de Coimbra, Coimbra, Portugal.

Accepted for publication March 21, 2016.

This work was partially funded by the European Society for Paediatric Infectious Diseases (ESPID.org) and Above and Beyond (aboveandbeyond.org.uk). These funders had no role in study design, data collection and analysis nor preparation of the manuscript.

A.F. is employed by the University of Bristol and University Hospitals Bristol NHS Foundation Trust. Before October 2014, both institutions, but not A.F., have received funding for research conducted by A.F. and for consultancy and lectures from Pfizer, GSK, SPMSD and Novartis, who manufacture licensed and developmental meningococcal vaccines. S.F. is employed by the University of Southampton. This institution, but not S.F., has received funding for research conducted by S.F. and for Advisory Board participation from Pfizer, GSK, SPMSD and Novartis, who manufacture licensed and developmental meningococcal vaccines. P.H. was employed by St. George’s, University of London (SGUL). SGUL, but not P.H., has received funding for research conducted by P.H. and P.H. has been a consultant for Pfizer and Novartis, who manufacture licensed and developmental meningococcal vaccines, but has not received any funding for this. L.J. has received financial support for the costs of attending medical conferences from SPMSD. ASIC (Associação de Saúde Infantil de Coimbra, Portugal), but not F.R., has received funding for research conducted by F.R. from Pfizer and for consultancy and/or lectures from Pfizer, GSK, SPMSD and Novartis, who manufacture licensed and developmental meningococcal vaccines. All the other authors have no conflicts of interest to disclose.

Address for correspondence: Adam Finn, PhD, Bristol Children’s Vaccine Centre, Level 6, UHB Education and Research Centre, Upper Maudlin St., Bristol, BS2 8AE, United Kingdom. E-mail: Adam.Finn@bristol.ac.uk.

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