Hépatite A: De l'évidence au piège diagnostique

Following the improvement of the hygiene conditions, the incidence of hepatitis A decreased in France. Nevertheless the Hepatitis A virus (HAV) remains the first cause of acute viral hepatitis. The number of subjects which are not immunized against HAV, is increasing, notably adult people, prone to develop symptomatic and potentially severe hepatitis A. The diagnosis, of hepatitis A is based on the detection of anti-HAV IgM in the serum. This marker, in spite of satisfactory sensitivity and specificity, can be wrong during polyclonal activation of the immune system, among individuals who were previously immunized against HAV. In this context, the measure of the anti-HAV IgG avidity allows to avoid a diagnostic error by highlighting an old hepatitis A. About less frequent prolonged or relapsing hepatitis A, the detection of HAV RNA by RT-PCR also supports the indirect diagnosis. Together these markers of expertise allow a reliable diagnosis of hepatitis A, while remaining reserved for some laboratories. They usefully complete the setting up of the mandatory declaration of hepatitis A, for a better knowledge of hepatitis A epidemiology, in order to guide the vaccine policy against this infection.