A Study of Fatal Cases of Group B Meningococcal Disease Using Non-culture Multilocus Sequence Typing and porA Sequence Typing

Carr, Anthony (2010) A Study of Fatal Cases of Group B Meningococcal Disease Using Non-culture Multilocus Sequence Typing and porA Sequence Typing. Doctoral thesis (PhD), Manchester Metropolitan University.

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Abstract

Since the introduction of the UK MenC vaccine programme in November 1999 there has been a 97% decrease in the number of confirmed group C meningococcal disease cases. However, in the year of introduction and the subsequent two years an increase in the numbers of group B cases was noted. Meningococcal infection may be microbiologically confirmed by culture and non culture methods. The introduction by the Meningococcal Reference Unit (MRU) of diagnostic polymerase chain reaction (PCR) testing in 1996 dramatically increased the number of cases ascertained solely by PCR, currently over 50%. Routinely cases determined by PCR only are confirmed to serogroup level and are not characterised further. This study was carried out to investigate whether the application of non culture DNA sequence typing which had recently been developed by the Heath Protection Agency could improve surveillance of meningococcal disease, and to determine if the increase in the number of observed group B cases was associated with particular meningococcal clones. The non culture DNA sequence typing of the porA antigen gene and of the seven genes of the Multilocus sequence typing (MLST) scheme was undertaken. Archived samples from one year before and two years following the immunisation programme, 96 samples in total, were analyzed using nested amplification and DNA sequence typing. The non culture group B fatal case data were also compared to other available molecular typing datasets. Results showed that there was no significant change in predominating group B clones and therefore no significant epidemiological shift in the meningococci causing group B disease, including fatalities, in the years 1999-2001. It was found by the combination of culture and non culture data that the two predominating clonal complexes causing fatal disease were ST41/44 lineage3 (36.3% pre and 30.8% post immunisation) and ST269 (22.4% pre and 31.9% post immunisation). This provided reassurance that the epidemiology of group B meningococcal disease was not impacted by the group C immunisation programme, and in particular that there was no noted proliferation of the hyper invasive ST11 clonal complex among group B disease (there were no fatal ST11 group B cases pre and 4.4% post immunisation). The porA and MLST data is important for group B vaccine development, which is informed by the monitoring of population shift among group B meningococci. In addition the non culture sequence typing methods described here have subsequently been applied to case cluster and outbreak investigation by the MRU. Incidents involving patients diagnosed by both non culture and culture methods are now able to be resolved.