summaries may give misleading impressions of the incidence of disease to policy-makers and program planners.

Identifying Chronic Infections

Given that both hepatitis B and hepatitis C infections are largely asymptomatic, most people do not receive a diagnosis until the infection is chronic. For hepatitis B, the chance of developing a chronic infection varies with age at the time of infection.

In persons over 6 years old, the vast majority of acute HBV infections are self-limited (Hyams, 1995). However, hepatitis B infections become chronic in over 90% of infants who are infected at birth or in the first year of life and in 30% of children who are infected at the age of 1–5 years (Pungpapong et al., 2007). Although hepatitis B surface antigen (HBsAg) is detectable within 4–10 weeks after infection, it is indicative of chronic HBV infection only if it persists for more than 6 months (Koff, 2004). An accurate diagnosis of chronic hepatitis B may therefore require the reporting of multiple serologic markers at more than one time (Koff, 2004).

For disease-surveillance purposes, it can be challenging for health departments to obtain the complete laboratory results that are necessary to classify a chronic hepatitis B case according to CDC’s case definitions (see Box 2-4). In general, a full hepatitis B panel (including any negative results for IgM anti-HBc) is required or two HBsAg results at least 6 months apart. Although states govern laboratory-reporting requirements in their jurisdictions, negative test results are generally not reportable and must be actively obtained. CDC’s Guidelines for Viral Hepatitis Surveillance and Case Management recommend that only positive HBsAg-test results be reported, but this test alone is inadequate to distinguish acute from chronic infection. Automated systems attached to electronic medical records may help to address surveillance for chronic HBV cases in the future, but in the meantime many diagnoses of chronic HBV infection probably will not be correctly captured and classified as confirmed cases (CDC, 2005a).

Surveillance for chronic HCV infection also presents challenges (see Box 2-5). In adults, about 15–25% of acute hepatitis C infections resolve spontaneously (Villano et al., 1999). That may increase to about 45% in children and young adults (Vogt et al., 1999). The presence of HCV RNA is generally detected within 1 week of infection (Mosley et al., 2005), but antibodies to HCV (anti-HCV) can be detected in only 50–70% of infected persons at the onset of symptoms; this increases to more than 90% after 3 months (NIH, 2002). A chronic infection is characterized by the persistent presence of HCV RNA for at least 6 months (NIH, 2002).

Typically, when a patient presents for HCV testing, the first test that is conducted is for the presence of anti-HCV. This test is generally an en-

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