Passive smoking increases the risk of bacterial meningitis in children

NICE’s Eyes on Evidence newsletter reports on a meta-analysis of observational studies looking at the incidence of bacterial meningococcal disease in relation to exposure to passive smoking.

Bacterial meningitis is rare, which makes it hard to study.  There are only 2 to 6 cases per 100,000 people in the UK every year, with a mortality rate of 10%.  The risk is highest in children around six months of age.

This review is important because it highlights the need to reduce exposure to second-hand smoke in children and young people, including unborn children.


The reviewers searched Medline, PsychINFO, EMBASE and CAB Abstracts for observational studies assessing the relationship between passive smoking and meningococcal disease.

Passive smoking was identified by self-reports or saliva testing, whilst invasive meningococcal disease was established by clinical diagnosis and/or by laboratory confirmation.

Two independent reviewers assessed each study for relevance and methodological quality.  Meta-analysis was carried out on the effect of exposure to second-hand smoke on the risk of meningitis, expressed as an odds ratio.


Child chastises a smoking adult

The meta-analysis found that more exposure to cigarette smoke was associated with more risk of meningitis

17 studies were included, comprising two large cohort studies and 15 case-control studies.  When the data from these studies were pooled in the meta-analysis, they found that people exposed to passive smoking in the home had 2.18 times the odds of getting meningitis compared with people not exposed.

The reviewers detected potential publication bias in the studies.  To account for this, they adjusted their analysis and arrived at an estimated odds ratio of 1.59 (95% CI 1.17 to 2.15)

which translates to an additional 350 cases of invasive meningococcal disease per year [in England] arising from exposure to smoking in the home.


  • The literature search was carried out in June 2012.
  • Although this evidence looks convincing, it could be that passive smoking is acting as a marker for other factors.  The studies were too heterogeneous for the reviewers to adjust fully for other confounders.
  • However, there was some evidence of a dose-reponse relationship, with those exposed via their mother smoking during pregnancy and/or postnatally showing the greatest increase in risk, alongside those in households where both parents smoke.
  • The reviewers made conservative assumptions about the possible effects of publication bias.


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Douglas Badenoch

Douglas Badenoch
I am an information scientist with an interest in making knowledge from systematic research more accessible to people who need it. This means you. I've been attempting this in the area of Evidence-Based Health Care since 1995. So far the results have been mixed. For some reason we expected busy clinicians to search databases and appraise papers instead of seeing patients. We also expected publishers to make the research freely available to the people who paid for it.. Ha! Hence The National Elf service.

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