Mathematics helps explain meningococcal meningitis outbreaks

Outbreaks of meningococcal meningitis depend on small differences in the pathogenicity of different bacterial strains, a new report indicates.

About 5 per cent - 25 per cent of individuals carry meningococcal bacteria but do not have meningococcal disease. Only about 0.01 per cent of those carrying the bacteria actually contract meningitis or septicaemia.

Previous research has shown that meningococci vary in the ability to cause the disease depending on strain type. Approximately ten hyperinvasive strains are responsible for the majority of recent meningococcal disease outbreaks.

The research team, funded by The Wellcome Trust and consisting of Vincent Jansen and Nico Stollenwerk from Royal Holloway - University of London, and co-investigator Martin Maiden, University of Oxford, developed a mathematical model to determine whether the diversity of strains is related to outbreaks of meningococcal disease. The study shows that large outbreaks occur if meningococcal strains with a slightly higher than average disease-causing potential appear in the population.

Paradoxically, strains that have only a weak potential to cause meningococcal disease are most likely to cause large outbreaks. This has implications for the control and management of meningococcal disease outbreaks.