Prevalence and persistence of Neisseria meningitidis carriage in Swedish university students

Abstract

The bacterium Neisseria meningitidis causes life-threatening disease worldwide, typically with a clinical presentation of sepsis or meningitis, but can be carried asymptomatically as part of the normal human oropharyngeal microbiota. The aim of this study was to examine N. meningitidis carriage with regard to prevalence, risk factors for carriage, distribution of meningococcal lineages and persistence of meningococcal carriage. Throat samples and data from a self-reported questionnaire were obtained from 2744 university students (median age: 23 years) at a university in Sweden on four occasions during a 12-month period. Meningococcal isolates were characterised using whole-genome sequencing. The carriage rate among the students was 9.1% (319/3488; 95% CI 8.2-10.1). Factors associated with higher carriage rate were age ≤22 years, previous tonsillectomy, cigarette smoking, drinking alcohol and attending parties, pubs and clubs. Female gender and sharing a household with children aged 0-9 years were associated with lower carriage. The most frequent genogroups were capsule null locus (cnl), group B and group Y and the most commonly identified clonal complexes (cc) were cc198 and cc23. Persistent carriage with the same meningococcal strain for 12 months was observed in two students. Follow-up times exceeding 12 months are recommended for future studies investigating long-term carriage of N. meningitidis.

Keywords: Carriage; Neisseria meningitidis; Swedish snus; university students; whole genome sequencing.

Fig. 1.

Distribution of students (n = 2744) participating in different combinations of the four sample occasions. Right-hand side: numbers of students participating once (n = 2251), twice (n = 309), three times (n = 146), and four times (n = 38).

Fig. 2.

Flow chart of throat samples in the analysis of carriage of N. meningitidis. In 10 samples, culture was missed due to human error.

Fig. 3.

Phylogenetic relationships of N. meningitidis carriage isolates (n = 241) presented as a circular phylogram with the corresponding clonal complexes in the outermost circle, and the corresponding groups in the second outermost circle. Cnl = capsule null locus, NG/ND = non-groupable / no data. The scale of the tree indicates 1% genes with allele differences out of the analysed 1422 genes.