Genomic characteristics of meningococcal carriage amongst young adults in Malta

Abstract

BACKGROUND: Invasive meningococcal disease has an incidence of 0.4-3/100,000 in Malta. Meningococcal carriage studies shed light on the epidemiology, transmission, and pathogenesis of invasive meningococcal disease. This research aimed to investigate the prevalence and genomic characteristics of meningococcal carriage in young adults aged 18-24 years attending the only university in Malta.

METHODS: Two posterior pharyngeal swabs were taken from 404 university students, and tested for Neisseria meningitidis (Nm) by culture and polymerase chain reaction. Isolates were assigned a serogroup and genogroup, and underwent whole genome sequencing to identify sequence type (ST), clonal complex (CC) and Bexsero antigen sequence type (BAST). Diversity amongst carried isolates was assessed using Simpson’s Index of Diversity (D).

RESULTS: Twenty-five students (6.2%; 95% C.I. 4-9%) were carriers for Nm While most meningococcal isolates were non-serogroupable (n=14; 66.7%; 95% C.I. 43-85.4%), the predominant genogroup was B (n=9; 36%; 95% C.I. 18–57.5%), followed by Y (n=6; 24%; 95% C.I. 9.4 – 45.1%). Fourteen different ST distributed among 9 CC, and demonstrating 17 different BAST, were identified amongst the carried meningococcal isolates. There was a high degree of BAST diversity (D=0.98). CC53, CC23 and the hyperinvasive CC41/44 accounted for 4 (19%; 95% C.I. 5.4-41.9%), 4 (19%; 95% C.I. 5.4-41.9%) and 3 (14.3%; 95% C.I. 3-36.3%) of isolates respectively.

CONCLUSIONS: Our findings demonstrate a wide biodiversity in meningococcal carriage, with CC23, CC41/44 and CC53 important. The introduction of glycoconjugate MenACWY vaccines on the national immunisation schedule could reduce meningococcal carriage and potentially IMD in Malta.