Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (181 page)

   
HAV

   HAV infections, caused by a nonenveloped, single-stranded RNA picornavirus, occur worldwide.

   Only approximately 25% of patients with acute HAV infection report risk factors in the 2–6 weeks prior to onset of symptoms. Risk factors include close contact with a patient with documented HAV infection or person at increased risk for HAV infection, employment or attendance at a nursery, day care center or preschool, exposure to a foodborne or waterborne outbreak, or high-risk sexual practices.

   Overall, 68% of patients develop jaundice. Childhood infections are most commonly anicteric (>90%), whereas infections in adults are often severe, with icteric infection occurring in approximately 80% of patients. Most symptomatic infections resolve in 1–2 months. Rare cholestatic variants may remain symptomatic for months but eventually resolve completely. The fatality rate for HAV infection is <1% (0.02/100,000 population), most commonly in patients >75 years of age.

   The prodromal period after exposure is approximately 4 weeks (range 2 to 7 weeks). Fecal excretion of virus begins late in the prodromal phase. IgM appears in the late prodrome; IgM may remain detectable for 6–12 months. After 3 months, IgM levels usually begin to drop, whereas rising IgG levels are detected. IgG levels persist indefinitely. Acute liver failure is uncommon in HAV infection (0.1%). Chronic infection does not occur in HAV infections.

   
HAV diagnosis
:

   Anti-HAV-IgM positive: Acute infection

   Anti-HAV-IgM appears at the same time as symptoms in >99% of cases and peaks within the 1st month. IgM becomes undetectable within 12 (usually 6) months.

   The presence of anti-HAV-IgM confirms diagnosis of recent acute infection. Serial testing is usually not needed for diagnosis.

   Serum bilirubin is usually 5–10 times the normal level. Jaundice lasts a few days to 12 weeks. Patients are usually not infectious after the onset of jaundice.

   Serum AST and ALT are increased for 1–3 weeks.

   Relative lymphocytosis is frequent.