Population structure and capsular switching of invasive Neisseria meningitidis isolates in the pre-meningococcal conjugate vaccine era--United States, 2000-2005.
BACKGROUND
A quadrivalent meningococcal conjugate vaccine (MCV4) was licensed in the United States in 2005; no serogroup B vaccine is available. Neisseria meningitidis changes its capsular phenotype through capsular switching, which has implications for vaccines that do not protect against all serogroups.


METHODS
Meningococcal isolates from 10 Active Bacterial Core surveillance sites from 2000 through 2005 were analyzed to identify changes occurring after MCV4 licensure. Isolates were characterized by multilocus sequence typing (MLST) and outer membrane protein gene sequencing. Isolates expressing capsular polysaccharide different from that associated with the MLST lineage were considered to demonstrate capsular switching.


RESULTS
Among 1160 isolates, the most common genetic lineages were the sequence type (ST)-23, ST-32, ST-11, and ST-41/44 clonal complexes. Of serogroup B and Y isolates, 8 (1.5%) and 3 (0.9%), respectively, demonstrated capsular switching, compared with 36 (12.9%) for serogroup C (P < .001); most serogroup C switches were from virulent serogroup B and/or serogroup Y lineages.


CONCLUSIONS
A limited number of genetic lineages caused the majority of invasive meningococcal infections. A substantial proportion of isolates had evidence of capsular switching. The high prevalence of capsular switching requires surveillance to detect changes in the meningococcal population structure that may affect the effectiveness of meningococcal vaccines.
Harrison
Lee H
LH
Department of International Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, USA. lharriso@edc.pitt.edu
Shutt
Kathleen A
KA
Schmink
Susanna E
SE
Marsh
Jane W
JW
Harcourt
Brian H
BH
Wang
Xin
X
Whitney
Anne M
AM
Stephens
David S
DS
Cohn
Amanda A
AA
Messonnier
Nancy E
NE
Mayer
Leonard W
LW
D000940:Antigenic Variation / Q000235:genetics*; D016667:Bacterial Capsules / Q000235:genetics*; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics; D015373:Bacterial Typing Techniques; D005838:Genotype; D006801:Humans; D008589:Meningococcal Infections / Q000382:microbiology / Q000517:prevention & control; D022401:Meningococcal Vaccines / Q000235:genetics / Q000276:immunology; D009345:Neisseria meningitidis / Q000235:genetics* / Q000302:isolation & purification; D038541:Neisseria meningitidis, Serogroup B / Q000235:genetics; D038542:Neisseria meningitidis, Serogroup C / Q000235:genetics; D038582:Neisseria meningitidis, Serogroup W-135 / Q000235:genetics; D038581:Neisseria meningitidis, Serogroup Y / Q000235:genetics; D017422:Sequence Analysis, DNA
D001425:Bacterial Outer Membrane Proteins; D022401:Meningococcal Vaccines