Evaluation of the surveillance of invasive meningococcal disease in Tunis: capture-recapture method

Objective: The objective of this study was to assess the completeness of the epidemiological surveillance system for invasive meningococcal diseases in greater Tunis. Patients and Methods: A six-year retrospective study (2003-2008) identified all cases of invasive meningococcal disease reported on Mandatory Notification records of the Tunis Regional Department of Health and those reported by the Tunis Children's hospital microbiology laboratory, considered to be the main source of diagnoses of invasive meningococcal disease in Greater Tunis. The "capture-recapture" method was applied. Results: Thirty-eight cases of invasive meningococcal disease reported to the Regional Department of Health and 47 cases provided by the children's hospital were analysed during the study period and 25 cases common to both sources were identified. The total number of cases of invasive meningococcal disease was estimated to be 71 (95% CI = [60-82]), using the capture-recapture method. Completeness rates were 53.5% (95% CI = [46.6 to 62.9]) for Mandatory Notification to the Regional Department of Health and 66.2% (95% CI = [57.6 to 77.8]) for children's hospital. Stratified analyses suggest that the two data sources were probably independent. Conclusions: The capture-recapture method applied to the invasive meningococcal disease surveillance system in Greater Tunis showed a poor sensitivity of the Mandatory Notification. Factors influencing under-reporting of cases should be identified to improve this surveillance.