Clinical presentation of invasive disease caused by Neisseria meningitidis serogroup Y in Sweden, 1995 to 2012

Abstract

Over the period 1995-2012, the incidence of invasive meningococcal disease (IMD) caused by Neisseria meningitidis serogroup Y (NmY) increased significantly in Sweden. This is mainly due to the emergence of a predominant cluster named strain type YI subtype 1, belonging to the ST-23 clonal complex (cc). The aim of this study was to examine the clinical picture of patients with invasive disease caused by NmY and to analyse whether the predominant cluster exhibits certain clinical characteristics that might explain the increased incidence. In this retrospective observational study, the medical records available from patients with IMD caused by Nm serogroup Y in Sweden between 1995 and 2012 were systematically reviewed. Patient characteristics, in-hospital findings and outcome were studied and differences between the dominating cluster and other isolates were analysed. Medical records from 175 of 191 patients were retrieved. The median age was 62 years. The all-cause mortality within 30 days of admission was 9% (15/175) in the whole material; 4% (2/54) in the cohort with strain type YI subtype 1 and 11% (12/121) among patients with other isolates. Thirty-three per cent of the patients were diagnosed with meningitis, 19% with pneumonia, 10% with arthritis and 35% were found to have bacteraemia but no apparent organ manifestation. This survey included cases with an aggressive clinical course as well as cases with a relatively mild clinical presentation. There was a trend towards lower mortality and less-severe disease in the cohort with strain type YI subtype 1 compared with the group with other isolates.

Keywords: Neisseria meningitidis; Neisseria meningitidis serogroup Y; Invasive meningococcal disease; Sweden; meningococcal disease.

Fig. 1.

Neighbour-Net graph constructed with 1241 of 1600 core genes, as defined in the PubMLST database, analysed on isolates from patients with NmY IMD in Sweden 1995–2012. Isolates from the most prevalent NmY strain types (YI, YII, YII and YIV) are found in the respective coloured areas. The YI strain type is amplified to visualise the close genetic relationships between clusters, where the dominating clusters subtype 1 and subtype 2 have been encircled, based on analysis of 1387 core genes. The genetic distance was defined as number of loci with allelic differences.

Fig. 2.

Age distribution of the 175 patients with serogroup Y IMD in Sweden 1995–2012 presented as total numbers, and also presented according to strain type YI subtype 1 and other isolates.