Under-reporting in hepatitis B notifications.

Notification and laboratory data for the period January 1985-December 1988 were compared in order to estimate: (i) the minimum level of under-reporting of hepatitis B; and (ii) the consistency of the level of under-reporting, both regionally and nationally. Ratios between hepatitis B notifications and positive hepatitis B laboratory tests (reporting ratios) were calculated to quantify the discrepancy between these parameters. There were at least 7 positive hepatitis B laboratory results for each notified case of hepatitis B during each year studied. The differences between the national reporting ratios for each of the study years were small, indicating that nationally the level of reporting of hepatitis B is fairly consistent. The Cape region had the highest and most constant level of hepatitis B reporting compared with other regions. We conclude that the national incidence of hepatitis B is at least 7 times higher than that calculated from notification data. Further, the inter-year analysis of hepatitis B notification data to identify trends nationally and within the Cape region is valid. However, caution is called for when comparing the incidence rates between regions due to inter-region and region-specific inter-year inconsistencies in reporting levels.