Clonal waves of Neisseria colonisation and disease in the African meningitis belt: eight- year longitudinal study in northern Ghana.
BACKGROUND
The Kassena-Nankana District of northern Ghana lies in the African "meningitis belt" where epidemics of meningococcal meningitis have been reoccurring every eight to 12 years for the last 100 years. The dynamics of meningococcal colonisation and disease are incompletely understood, and hence we embarked on a long-term study to determine how levels of colonisation with different bacterial serogroups change over time, and how the patterns of disease relate to such changes.


RESULTS
Between February 1998 and November 2005, pharyngeal carriage of Neisseria meningitidis in the Kassena-Nankana District was studied by twice-yearly colonisation surveys. Meningococcal disease was monitored throughout the eight-year study period, and patient isolates were compared to the colonisation isolates. The overall meningococcal colonisation rate of the study population was 6.0%. All culture-confirmed patient isolates and the majority of carriage isolates were associated with three sequential waves of colonisation with encapsulated (A ST5, X ST751, and A ST7) meningococci. Compared to industrialised countries, the colonising meningococcal population was less constant in genotype composition over time and was genetically less diverse during the peaks of the colonisation waves, and a smaller proportion of the isolates was nonserogroupable. We observed a broad age range in the healthy carriers, resembling that of meningitis patients during large disease epidemics.


CONCLUSIONS
The observed lack of a temporally stable and genetically diverse resident pharyngeal flora of meningococci might contribute to the susceptibility to meningococcal disease epidemics of residents in the African meningitis belt. Because capsular conjugate vaccines are known to impact meningococcal carriage, effects on herd immunity and potential serogroup replacement should be monitored following the introduction of such vaccines.
Leimkugel
Julia
J
Swiss Tropical Institute, Basel, Switzerland.
Hodgson
Abraham
A
Forgor
Abudulai Adams
AA
Pflüger
Valentin
V
Dangy
Jean-Pierre
JP
Smith
Tom
T
Achtman
Mark
M
Gagneux
Sébastien
S
Pluschke
Gerd
G
D000293:Adolescent; D000328:Adult; D000367:Age Factors; D002648:Child; D002675:Child, Preschool; D004196:Disease Outbreaks; D005260:Female; D005869:Ghana; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008589:Meningococcal Infections / Q000150:complications / Q000175:diagnosis* / Q000453:epidemiology* / Q000382:microbiology; D008875:Middle Aged; D009345:Neisseria meningitidis / Q000378:metabolism; D012737:Sex Factors