Estimation of the incidence of invasive meningococcal disease using a capture-recapture model based on two independent surveillance systems

Background: Invasive meningococcal disease (IMD) is an urgent notifiable disease and its early notification is essential to prevent cases. The objective of the study was to assess the sensitivity of two independent surveillance systems, the statutory disease reporting system (SDR) and the microbiological reporting system (MRS), and to estimate the incidence of IMD. Methods: : The study was performed in Catalonia, Spain, between 2011 and 2015. The variables collected were age, sex, year of report, size of municipality (< 10,000 and ≥ 10,000), clinical form, death, serogroup, country of birth and type of reporting centre (private and public). The capture-recapture analysis and 95% confidence intervals were calculated using the Chapman formula. Multinomial logistic regression was performed for adjusted estimation. Results: : The sensitivity of the two combined surveillance systems was 88.5% (85.0-92.0). SDR had greater sensitivity than the MRS (67.9%; 62.7-73.1 vs. 64.7%; 59.4-70.0). In 2014-2015, the sensitivity of both systems was higher (80.6%; 73.2–87.9 vs. 73.4%; 65.2–81.6) than in 2011-2013 (59.3%; 52.6–66.0 vs. 58.3%; 51.6–65.1). In private centres, the sensitivity was higher for SDR than for MRS (100%; 100–100 vs. 4.8%; -4.4–13.9). The adjusted estimate of cases was lower than that obtained using the Chapman formula (279; 266–296 vs. 313; 295–330). The estimated adjusted incidence of IMD was 0.7/100,000 persons-year. Conclusions: : The sensitivity of enhanced surveillance through the combination of two complementary sources was higher than for the sources individually. Factors associated with under-reporting in different systems should be analysed to improve IMD surveillance.