Laboratory quality control in a multicentre meningococcal carriage study in Burkina Faso

To investigate the potential herd immunity effect of MenAfriVac, a new conjugate vaccine against serogroup A Neisseria meningitidis, a multiple cross-sectional carriage study was conducted in three districts in Burkina Faso in 2009, yielding a total of 20 326 oropharyngeal samples. A major challenge was the harmonisation of operational procedures and ensuring the reliability of results. Here we describe the laboratory quality control (QC) system that was implemented. Laboratory analysis performed by three local laboratories included colony morphology assessment, oxidase test, Gram stain, β-galactosidase activity using o-nitrophenyl-β-galactopyranoside (ONPG), γ-glutamyl transferase (GGT) activity and slide agglutination serogrouping. Internal QC was performed on media, reagents, laboratory equipment and field conditions. Confirmation of results and molecular characterisation was performed at the Norwegian Institute of Public Health (Oslo, Norway). External QC was performed on 3% of specimens where no colonies morphologically resembling N. meningitidis had been identified and on 10% of non-ONPG−/GGT+ isolates. The QC system was a critical element: it identified logistical and operational problems in real time and ensured accuracy of the final data. The overall N. meningitidis carriage prevalence (3.98%) was probably slightly underestimated and the calculated true prevalence was 4.48%. The components of the presented QC system can easily be implemented in any other laboratory study.