Viral hepatitis surveillance in 1993 revealed several important changes from earlier years. First, total cases reported to the VHSP declined more than 51% from 1990 to 1993, as a result of both real declines in the incidence of hepatitis A and B, and a number of states that previously reported now submitting fewer or none of their cases to the VHSP. Second, the use of serologic tests to diagnose the specific type of hepatitis has declined, with fewer reported cases being diagnosed on the basis of tests for both hepatitis A and B. Third, analysis of trends in risk factors for the acquisition of the different types of hepatitis indicated that injection drug use has declined dramatically for hepatitis A, B, and hepatitis C/NANB. Finally, more widespread use of hepatitis B vaccine may be having an effect on the number of hepatitis B cases acquired by heterosexual activity.

Underreporting and incomplete case ascertainment are potential sources of inaccuracy and may lead to inaccurate conclusions from surveillance data, particularly in the relative frequencies of reported risk factors.⁽²¹⁾ Since case ascertainment is dependent on the availability of sensitive and specific serologic tests, estimates of the frequency of disease types such as hepatitis C/NANB, for which there are no markers of acute disease, are likely to be the least reliable. The analysis of VHSP data on biases in the reporting of hepatitis B and hepatitis C/NANB showed that consistent reporting practices are critical for the accurate interpretation of surveillance data in this country. In addition, national data are averaged over many regions with potentially large geographic differences in risk factors and disease incidence. Therefore, the overall frequencies of various risk factors may not reflect their importance in smaller geographic areas.

Despite the drawbacks associated with a passive surveillance system, the data collected through the VHSP are essential for monitoring trends in the epidemiologic characteristics of the various types of viral hepatitis. These data are also valuable for monitoring the impact of prevention programs on disease in various high-risk groups, such as those targeted to receive hepatitis B vaccine. The recently recommended program for the universal immunization of infants for hepatitis B was the direct result of the analysis of surveillance data, and provides evidence that contributors to the VHSP have made a positive impact on public health.

Many dedicated public health practitioners, local medical authorities, and public health communities contribute to this surveillance system through their timely diagnosis and reporting of hepatitis cases. We are grateful for their continued participation and encourage them to continue to improve their use of serologic testing, their consistency in reporting, and the quality of the information they provide.