Meningococcal disease in urban south western Sydney, 1990-1994

Differences in the population structure of Neisseria meningitidis in two Australian states: Victoria and Western Australia

Neisseria meningitidis is the causative agent of invasive meningococcal disease (IMD). A recombinant vaccine called Bexsero® incorporates four subcapsular antigens (fHbp, NHBA, NadA and PorA) which are used to assign a Bexsero® antigen sequence type (BAST) to each meningococcal strain. The vaccine elicits an immune response against combinations of variants of these antigens which have been grouped into specific BAST profiles that have been shown to have different distributions within geographical locations thus potentially affecting the efficacy of the vaccine. In this study, invasive meningococcal disease isolates from the western seaboard of Australia (Western Australia; WA) were compared to those from the south-eastern seaboard (Victoria; VIC) from 2008 to 2012. Whole-genome sequencing (WGS) of 131 meningococci from VIC and 70 meningococci from WA were analysed for MLST, FetA and BAST profiling. Serogroup B predominated in both jurisdictions and a total of 10 MLST clonal complexes (cc) were shared by both states. Isolates belonging to cc22, cc103 and cc1157 were unique to VIC whilst isolates from cc60 and cc212 were unique to WA. Clonal complex 41/44 represented one-third of the meningococcal population in each state but the predominant ST was locally different: ST-6058 in VIC and ST-146 in WA. Of the 108 BAST profiles identified in this collection, only 9 BASTs were simultaneously observed in both states. A significantly larger proportion of isolates in VIC harboured alleles for the NHBA-2 peptide and fHbp-1, antigenic variants predicted to be covered by the Bexsero® vaccine. The estimate for vaccine coverage in WA (47.1% [95% CI: 41.1-53.1%]) was significantly lower than that in VIC (66.4% [95% CI: 62.3-70.5%]). In conclusion, the antigenic structure of meningococci causing invasive disease in two geographically distinct states of Australia differed significantly during the study period which may affect vaccine effectiveness and highlights the need for representative surveillance when predicting potential impact of meningococcal B vaccines.

Australia's century of meningococcal disease: development and the changing ecology of an accidental pathogen

Trends in meningococcal disease (MD) over the 20th century in Australia, as in other industrialised countries, have been characterised by epidemics during the two World Wars, a transient rise in incidence in the 1950s followed by endemic disease, and in the 1980s the emergence of a sustained hypersporadic phase. Epidemics occur at times of social upheaval and among marginalised populations, and resolve when living conditions improve. Periodic serogroup A epidemics have been replaced since the 1950s by endemic disease caused mainly by serogroups B and C meningococci. The current hypersporadic plateau in Australia, as in other industrialised countries, is associated with the intercontinental spread of hypervirulent clones of meningococci. The conjugate serogroup C vaccine has reduced the incidence of MD and carriage rates of serogroup C meningococci. However, the vaccine is expensive and its long-term impact on the emergence of non-vaccine strains and on nasopharyngeal microecology is unknown. A rising incidence of MD should not be viewed as the action of a virulent microbe exploiting a vulnerable population, but as the emergence of an "accidental pathogen" from an evolving host-microbial ecology. While it is essential to monitor the impact of vaccines on this ecology, we must find ways that can optimise our coexistence with microbes.

Survey of blood cultures from five community hospitals in south-western Sydney, Australia, 1993-1994

BACKGROUND

Blood culture results have profound implications for patients. Comprehensive overviews of blood cultures have been uncommon, and focused on tertiary referral hospitals.

AIM

To present a review of blood culture results from a laboratory servicing community hospitals in Sydney, Australia.

METHODS

Retrospective chart review of patients with positive blood cultures from 1 June 1993 to 31 May 1994.

RESULTS

During the survey period there were 107,382 hospital admissions; 12,109 blood culture sets from 9292 patients were processed. Of these 1197 sets were positive, representing 974 febrile episodes in 923 patients. There were 476 episodes of contamination. Of the episodes of true bacteraemia, Escherichia coli was isolated in 139, Staphylococcus aureus in 91 (22 methicillin-resistant), other enterobacteriaceae in 60, and Streptococcus pneumoniae in 5 1. The diagnoses attributable to bacteraemia included intravenous catheter-related sepsis (122 episodes), urinary tract infection (88), bacteraemia from unknown source (79), intra-abdominal and biliary sepsis (91), pneumonia (35), and meningitis (21). Sixty-eight patients died directly due to bacteraemia. Multivariate analysis showed underlying disease (OR 3.97) or shock (OR 28.1) predicted death. Blood cultures confirmed clinical diagnoses in 258 episodes, but made a de novo diagnosis in 205 episodes.

CONCLUSIONS

This study describes the clinical and laboratory features of bacteraemias occurring in smaller public hospitals, as distinct from tertiary referral centres. It demonstrated that intravenous catheter-related sepsis was very common in smaller hospitals. The clinical diagnosis was frequently confirmed, and a de novo diagnosis was often established by a positive blood culture. Unfortunately nearly half the positive blood cultures represented contamination.