Changing carriage rate of Neisseria meningitidis among university students during the first week of term: cross sectional study
BMJ 2000; 320 doi: https://doi.org/10.1136/bmj.320.7238.846 (Published 25 March 2000) Cite this as: BMJ 2000;320:846All rapid responses
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Editor
Neal et al’s paper documenting risk factors for acquisition of Neisseria
meningitidis amongst university students helps further our understanding
of the aetiology of university outbreaks of meningococcal disease (1). A
number of outbreaks have now been linked to bars and nightclubs (2,3). By
showing that social factors such as bar attendance influence acquisition,
the study helps substantiate evidence that social behaviour is important
in determining outbreak occurrence.
However, the three-fold rise in carriage rates in the first 4-days of
term is unexpected. The initial carriage rate (6.9%), as the authors
acknowledge, is surprisingly low. In 16-24 year olds, carriage rates in
both outbreak and non-outbreak situations are usually 20% or higher (4,
5). The sudden increase, in a cross-sectional study, to rates that would
be normal for this age group suggests potential confounding. Carriage has
been clearly documented to vary with age and gender (2,4,5), yet no
comparison of the age and sex of the 4 groups is presented, nor are these
variables included in the regression analysis that examines risk factors
for carriage.
The study shows that virulent C2a strains are acquired more rapidly
over the term than other strains. Rapid acquisition of disease causing
strains was also suggested in the Cardiff and Southampton University
outbreaks, where low carriage rates of serogroup C outbreak organisms were
documented along with very close clustering of the cases in time(2). If a
rapid increase in carriage does occur at the start of term, and
particularly if virulent C2a strains are transmitted preferentially as the
study suggests, one would expect the rise in carriage to be accompanied by
a dramatic peak in disease incidence in the first 1-2 weeks of term. Yet
the peak of cases usually occurs after a 3-5 week delay(1). The
alternative, albeit unlikely explanation is that acquisition of different
strains varies over time with acquisition of C2a strains occurring later.
It would be useful if the authors could present further analysis to
help rule out confounding as an explanation for the study’s unexpected
initial findings. Although variation in sensitivity of swabbing is
difficult to exclude, the authors have otherwise done their best to
validate the data. Nevertheless a cohort study using sensitive
microbiological techniques would be required to confirm whether the rapid
rise in carriage at the start of term is due to a true rise in
acquisition, whether differential acquisition of virulent and non-virulent
strains occurs or alternative explanations account for the findings.
Anna Gilmore
Senior registrar in Public Health Medicine and Visiting
fellow,
London School of Hygiene and Tropical Medicine, 50 Bedford Square, London,
anna.gilmore@lshtm.ac.uk
James Stuart
Consultant Epidemiologist
Communicable Disease Surveillance Centre (South West), Public Health
Laboratory, Gloucester
1. Neal KR, Nguyen-Van-Tam JS, Jeffrey N, Slack RCB, Madeley RJ, Ait-
Tahar K et al. Changing carriage rate of Neisseria meningitidis among
university students during the first week of term: cross sectional study.
BMJ 2000;320:846-9.
2 Gilmore A, Jones G, Barker M, Soltanpoor N, Stuart JM.
Meningococcal disease at the Unversity of Southampton: outbreak
investigation. Epidemiol Infect 1999;123:185-92.
3 Imrey PB, Jackson LA, Ludwinski PH, England AC III, Fella GA, Fox
BC et al. Meningococcal carriage, alchohol consumption and campus bar
patronage in a serogroup C meningocccal disease outbreak. J Clin Microbiol
1995:33: 3133-7.
4 Cartwright KAC, Stuart JM, Jones DM, Noah ND, The Stonehouse
survey: nasopharyngeal carriage of meningocci and Neisseria lactamica.
Epidemiol Infect 1987;99:591-601.
5 Caugant DA, Hoiby EA, Magnus P et al. Asymptomatic carriage of
Neisseria meningitidis in a randomly sampled population. J Clin Microbiol
1994;32:323-30.
Competing interests: No competing interests
The author Kieth R Neal and co-workers are to be congratulated on a
well designed study depicting the
changing carrier rate of N.Meningitides, with an impressive documenttation
of rising incidence of the carrier rate during the first term in students
at the university.
N. Meningitides bacteria have antigenic polysacchrides in the outer
capsule, that form the basis for 13 serogroups.
The Authors plea for vaccination opens the way to implement
routine vaccination in all university health services for enrolling
students.However, immunization through vaccination is possible only
against serogroup A,C,Y, and
W-135. As yet immunization against serogroup B is not yet available.
May I say from personal experience, that certain individuals with
influenza A virus, or asplenia, or certain genetically linked protein
disorders, as well as immunocompromised patients have a higher risk for
developing
meningitis than the population at large and therefore such disorders when
present should alert physicians in university health services and the
armed forces to immunize against N. Meningitides, in addition to
susceptible carrier age groups.Hence prevention should go beyond
antibiotics for contacts and for carriers of the N.Meningitides bacteria.
Munir E Nassar, M.D., FACP
Competing interests: No competing interests
Sex related factors are important in meningococcal carriage
Editor- Neil et al reported a rapid increase in
meningococcal carriage among first year students soon
after arrival at university and attributed this to
increased in social mixing.1 Asymptomatic
nasopharyngeal carriers are the usual source of
infection.
It is already known that carriage rates are high in
young adults, in people who live in conditions of
severe overcrowding, and in military recruits in the
absence of overcrowding. In the very young and old
carriage rates are low and more males than females are
carriers. Furthermore it is also known that some
factors such as upper respiratory infection, previous
tonsillectomy and smoking may increase the likelihood
of carriage.
However, multiple sexual partners may also have an
effect on carriage rates. An initial study
investigated the sexual behaviour and carriage of
menigococci in 496 patients attending a genitourinary
medicine clinic. Just over one quarter were carriers
of the bacteria, and the rate was slightly raised in
those who had had 10 or more partners in their life
time.2
The morbidity and mortality caused by meningococcal
meningitis remains significant despite advances in
antimicrobial therapy and supportive care. At present
only secondary contacts of meningococcal disease
receive chemoprophylaxis. In the light of sexual
behaviour as a possible risk factor the recently
established immunisation programme against meningitis
C,(includes university students), must continue
perhaps with simultaneous primary chemoprophylaxis to
protect against other meningococcal strains. The
increased risk of infection associated with HIV
necessitates efforts at modifying sexual behaviour.
Further studies looking at effectiveness of options
such as universal screening and treatment of carriers
identified, and universal chemoprophylaxis3 in
eradicating meningococcal disease are required. It
must, however, be stressed that Neisseria meningitidis
is identified as a commensal bacterium – any link
between carriage and disease is indeed yet to be
established.
References:
1. Neal KR, Nguyen-van-Tam JS, Jeffery N et al.
Changing carriage rate of Neisseria meningitidis among
University students during the first week of term:
cross section study. BMJ 2000;320:846-9
2. Tayal SC, Rashid S, Muttu KMS and Hildreth AJ.
Meningococcal carriage: Prevalence and Sex Related
risk factors. J Inf 1997;34:101-5
3. Block C, Raz R, Frasch et al. Re-emergence of
meningococcal carriage on three year follow up of
Kibbutz population after whole community
chemoprophylaxis. Eur J Clin Microbiol Infec Dis
1993;12:505-11
*Dr. Sarup Tayal,
Consultant GU/HIV Physician
Department of Genito-Urinary Medicine,
Middlesbrough General Hospital, Middlesbrough TS5 5AZ
STayal8144@AOL.COM
Dr. Santosh Gupta,
Consultant Paediatrician
Hartlepool General Hospital, Hartlepool, TS24 9AH
SG1CP@AOL.COM
Address for correspondence: *Dr. Sarup Tayal
Competing interests: No competing interests