Hepatitis A surveillance: sensitivity of two information sources

Background: The frequency of mild forms of hepatitis A, especially in children, could lead to underreporting. The objective of the study was to investigate the sensitivity of two surveillance systems, mandatory Statutory Disease Reports and the Microbiological Reporting System of Catalonia, using capture-recapture techniques.

Methods: The study was conducted in Catalonia between 2011 and 2015. Hepatitis A cases reported to two independent surveillance systems were included: Statutory Disease Reports (SDR) and Microbiological Reporting System of Catalonia (MRS). The variables collected were: age, sex, year of declaration, size of municipality (< 10,000 and ≥ 10,000), country of birth (Spain or abroad), reporting centre (primary care/hospital) and notification method (electronic or paper). The capture-recapture analysis and the estimate of 95% confidence intervals were made using the Chapman formula for comparison of two sources, both for the estimate of the total number of cases and the stratification according to variables. Multinomial logistic regression was performed to obtain an adjusted estimate.

Results: The SDR had a greater overall sensitivity than the MRS (48.8%; 43.5-55.6 vs. 19.3%; 17.2-21.9). In cases aged < 15 years the sensitivity of both systems was higher (76.6%; 72.7-81 vs. 25.2%; 20.9-29.5) than in cases aged > 15 years (25.5%; 22.8-28.3 vs. 12.1%; 10-14.2). For those born in Spain, the sensitivity was 57.2% (49.6-67.4) in the SDR and 27.1% (23.5-31.9) in the MRS, lower than that for foreign-born patients (58%; 51.2-66.8 vs. 49.1%; 43.4-56.6). In electronically-reported cases, the sensitivity was much higher in the SDR than in the MRS (47.2%; 42.3-52.1 vs. 9.4%; 6.5-12.3). No differences were observed according to sex, size of municipality, and year of declaration or reporting centre. The estimated total number of cases using the Chapman formula was very similar to the adjusted estimate (1121; 985-1258 vs. 1120; 876-1525), indicating the robustness of the results.

Conclusions: The sensitivity of the SDR was greater than that of MRS, especially in patients aged < 15 years, although for patients born abroad the difference in sensitivity was lower. Reinforced surveillance combining the SDR and MRS improves the efficiency in the detection of cases.