Children exposed to secondhand smoke are more likely to get invasive meningococcal disease than children who are not exposed, according to a metaanalysis published in the journal PLoS Medicine.

Invasive meningococcal disease is a term that refers to when a person becomes infected with meningococcus bacteria. This infection can cause meningitis – inflammation of the lining around the brain and spinal cord – and septicaemia – blood poisoning. The bacterium is thought to be responsible for around 50,000 deaths a year worldwide, mainly among infants and adolescents.

To find out whether passive smoking could make children more vulnerable to meningococcus and other bacterial infections, researchers reviewed and analysed every previous study that had compared the occurrence of invasive bacterial disease and the presence of bacteria in the nose and throat in children exposed to secondhand smoke with occurrence in children not exposed to smoke – 42 studies in total.

The results showed that children exposed to secondhand smoke were twice as likely to get invasive meningococcal disease.

The study also found that passive smoking raised the risk of infection with streptococcal bacteria and Haemophilus influenzae type B, but this increase could not be distinguished from a chance finding. More studies would be needed to confirm whether secondhand smoke could be linked to these other bacterial infections.

The analysis was conducted by Professor Majid Ezzati, Chair in Global Environmental Health at Imperial College London’s School of Public Health, with colleagues at Harvard University and Medical Research Council (UK) Laboratories in The Gambia.

\”The results suggest that reducing children’s exposure to secondhand smoke, for example by parents stopping smoking or not smoking at home, could prevent deaths and illness caused by invasive bacterial diseases,\” Professor Ezzati said. \”It’s particularly important in poor countries, where few children have access to vaccinations against bacterial diseases, and where secondhand smoke exposure may even happen at school.

\”These diseases are particularly devastating in developing countries, and these are the countries where smoking is on the rise. We urgently need to take steps to reduce exposure of children to secondhand smoke, and also do more high-quality studies to investigate effects of secondhand smoke on other infections.\”

The study was funded by grants from the US National Institute of Environmental Health Sciences and the Bill & Melinda Gates Foundation.