Mathematical modelling of infection and disease due to Neisseria meningitidis and Neisseria lactamica

Background Invasive meningococcal disease, due to Neisseria meningitidis, i s an important cause of morbidity and mortality in young children and adole scents. Nasopharyngeal carriage of meningococci (MC), is most prevalent in young adults whereas carriage of Neisseria lactamica (LC), a related non-pa thogenic organism, is most prevalent in young children. The objective of th is study was to use modelling techniques to test hypotheses on the processe s that govern the incidence of meningococcal disease (MD). Methods Deterministic compartmental models were fitted to age structured da ta sets of MC, LC and MD. Results The model most consistent with the available data sets is one where LC inhibits MC, an inhibition that lasts for a mean of 4.7 years. The hypo thesis that LC also acts as a natural immunogen against MD was consistent w ith this model. The second peak of MD observed among adolescents could be d ue to the peak in the acquisition of MC in this age group. Conclusions The role of LC as a natural immunogen against asymptomatic and symptomatic meningococcal infection was consistent with available field dat a. If the introduction of novel meningococcal vaccines into a population ch anges the prevalence of MC or LC, this could have a substantial impact on t he effectiveness of immunization programmes. This paper demonstrates the po tential utility of modelling to estimate these effects.