—from Epidemiological Bulletin, Vol. 23 No. 2, June 2002—

Case Definition
Acute Viral Hepatitis

Rationale for surveillance
Estimates suggest that worldwide, there are 385 million carriers of hepatitis B virus and 170 million carriers of hepatitis C virus. More than 1 million deaths each year are attributable to hepatitis B. Transmission is mainly oral-faecal for hepatitis A and E, percutaneous for hepatitis B, C, and D and sexual for hepatitis B. The course of the disease may be fulminating (e.g., hepatitis E in pregnancy); chronic infection and severe sequelae occur for hepatitis B, C, and D. Prevention measures include transfusion safety, safe and appropriate use of injections, promotion of safe sexual practices, and (for hepatitis A and hepatitis B) immunization. Hepatitis B is targeted by WHO for reduced incidence/prevalence, by means of vaccination programs in children under 1 year of age.

Recommended case definition
Clinical description
Acute illness typically including acute jaundice, dark urine, anorexia, malaise, extreme fatigue, and right upper quadrant tenderness. Biological signs include increased urine urobilonogen and >2.5 times the upper limit of serum alanine aminotransferase.

Note: Most infections are asymptomatic in early childhood. A variable proportion of adult infections is asymptomatic.

Laboratory criteria for etiological diagnosis
– Hepatitis A: IgM anti-HAV positive
– Hepatitis B: IgM anti-HBc positive with or without HBsAg
– Non-A, non-B: IgM anti-HAV and IgM anti-HBc negative

Note 1: The anti-HBc IgM test, specific for acute infection, is not available in most countries. HbsAg, often available, cannot distinguish between acute new infections and exacerbations of chronic hepatitis B, although continued HBsAg seropositivity (>6 months) is an indicator of chronic infection.

Note 2: For patients negative for hepatitis A or B, further testing for a diagnosis of acute hepatitis C, D, and/or E is recommended:
– Hepatitis C: anti-HCV positive with compatible clinical-epidemiological data
– Hepatitis D: HBsAg positive or IgM anti-HBc positive plus anti-HDV positive (only as co-infection or super-infection of hepatitis B)
– Hepatitis E: IgM anti-HEV positive

Case classification
Suspected: A case that is compatible with the clinical description.
Probable: Not applicable.
Confirmed: A suspected case that is laboratory confirmed or, for hepatitis A only, a case compatible with the clinical description, in a person who has an epidemiological link with a laboratory-confirmed case of hepatitis A (i.e. household contact with an infected person during the 15-50 days before the onset of symptoms).

Recommended types of surveillance
– Routine monthly reporting of aggregated data of suspected cases, and if available, the number of confirmed cases of each type of hepatitis, from the peripheral level to intermediate and central levels
– Zero reporting required at all levels
– When countrywide surveillance is not possible, surveillance in sentinel areas or hospitals may provide useful information on potential sources of infection

All outbreaks should be investigated immediately and confirmed serologically.

Recommended minimum data elements
Aggregated data:
– Number of third doses of hepatitis B vaccine (HepB3) administered to infants (less than 1 year)
– Number of injections received in the 6 weeks to 6 months preceding symptoms of acute hepatitis (whatever the etiology)
– Number of suspect cases
– If available, number of confirmed cases for each type of hepatitis

Recommended data analyses, presentation, reports: (from multiple sources, in addition to surveillance data)
– HepB3 coverage in infants (less than 1 year) by year and geographic area.
– Incidence of acute viral hepatitis by year, month, geographical area, and (if data exist) by age group and type of virus.
– Proportion of all cases of chronic liver disease, cirrhosis, and primary liver cancer that are HbsAg positive or anti-HCV positive (see special aspects).
– Comparing the proportion of patients who received an injection in the 6 weeks to 6 months preceding symptoms among hepatitis A and hepatitis B cases helps to estimate the proportion of hepatitis B virus infections that are attributable to injections.

Principal uses of data for decision-making
– Monitor HepB3 immunization coverage by geographic area to measure areas with weak performance and take action.
– Investigate all suspected / reported outbreaks.
– Determine the specific cause of acute viral hepatitis cases (reported routinely or during outbreaks), so that corrective measures can be taken.
– Evaluate the effectiveness of injection safety programmes.
– Measure the proportion of acute viral hepatitis, chronic liver disease, cirrhosis, and primary liver cancer that are hepatitis B virus or hepatitis C virus carriers to:

- Determine the burden of the disease in the population;
- Prioritize among other diseases of public health importance; and
- Choose the proper strategies for control.

Special aspects
Accurate differential diagnosis of viral hepatitis types requires serological testing – unavailable in many developing countries. In developing countries where most infections occur asymptomatically, a low incidence of reported acute viral hepatitis disease should not be misinterpreted as a low incidence of viral hepatitis infection.

Understanding the epidemiology and impact of viral hepatitis requires enhanced surveillance and an understanding of the sequelae of hepatitis B, C and D virus infection, such as asymptomatic chronic infection, chronic hepatitis, cirrhosis, and primary liver cancer. This also requires data collection from sources not routinely used, including hospital surveillance data such as hospital discharges, and mortality (chronic hepatitis, cirrhosis, liver cancer) and cancer registers. Special sero-prevalence surveys may be needed to measure prevalence of hepatitis B and C infection in the general population and in special groups (health care workers, blood donors, pregnant women, military recruits, patients with liver disease, people on dialysis, haemophiliacs), and ethnic sub-populations.

Assessment for coverage of hepatitis B vaccine is similar to that for other vaccines. Hepatitis vaccine is given to infants (less than one year) (and in some industrial countries to adolescents), and to special groups such as health workers, primarily to prevent the development of chronic liver disease and liver cancer. Serological testing to document sero-conversion in children is usually not necessary: studies show that vaccine is 85% to 100% effective in preventing chronic infection.

Source: Adapted from “WHO Recommended Surveillance Standards, Second edition, October 1999”, WHO/CDS/CSR/ISR/99.2

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Epidemiological Bulletin, Vol. 23 No. 2, June 2002