Hepatitis A

Hepatitis A is the most common cause of acute viral hepatitis in the world.

Epidemiology

50% of the adult U.S. population has serological evidence of exposure.
The Hepatitis A virus (HAV) is highly endemic in developing countries.
Many cases are asymptomatic, so actual prevalence is likely 10x reported prevalence.
The population with highest incidence in the US is children who wear diapers. Infants and children are, in fact, the primary reservoir for HAV in the US.
Risk factors: 
-Ingestion of food or water contaminated with infected feces 
-Household or childcare center contact with infected patients 
-International travel 
-Illicit drug use 
-Men who have sex with men 
-Raw shellfish (which can concentrate HAV-contaminated water)

HAV is spread via the fecal-oral route.
HAV travels through the bloodstream to infect hepatocytes.
In the hepatocyte, the virus replicates quickly but causes minimal damage to the hepatocyte itself.
New viruses are released into the bile ducts; they then travel to the gut and into the stool.
It takes 2-3 weeks for the body's adaptive immune responses to fully activate. Until then, the virus multiplies and is released into the stool unchecked. As a result, the first phase of the HAV is without symptoms (as the virus itself does not kill hepatocytes).
CD8+ T cells destroy the infected liver cells. In some cases (especially in young children) there are few HAV-infected hepatocytes so liver damage is minimal.
When damage to the liver is more extensive, the classic symptoms of hepatitis arise: malaise, anorexia, fever, nausea, vomiting, and jaundice.
The HAV virus can be effectively eliminated by the immune system. There is no risk of chronic infection, and immunity after the infection is life-long.
Rarely, the HAV infection can cause significant liver damage and produce fulminant hepatic failure (FHF). FHF is very rare in the U.S.
HAV will be shed in the feces for weeks following the initial infection. The HAV can also live for weeks in dried feces. The virus is not effected by freezing or drying, which makes it highly transmissible.

Less than 10% of children <6 years old will have clinical evidence of disease. The incidence of symptomatic disease increases with age.
Signs and Symptoms: fever, nausea and vomiting, diarrhea, jaundice, anorexia, and malaise.
Unusual complications include fulminant hepatitis, cholestatic hepatitis, and recurrent hepatitis.
Laboratory evaluations may reveal elevated serum aminotransferases and bilirubin. Urine is often dark due to the presence of bilirubin.
Symptoms last 2-3 weeks in the majority of cases.
The HAV is more likely to cause severe liver damage in patients who are also infected with HCV or HBV, patients waiting or having undergone liver transplant, pregnant women, and patients with HIV+ status. HAV is especially dangerous in patients with chronic HCV.

The HAV grows really slowly in culture, so diagnosis is via detection of HAV antibodies.
Current or recent HAV infection is marked by anti-HAV IgM. IgM can usually be detected in serum one week after symptom onset. It will decline 3 to 6 months after infection.
Anti-HAV IgG appears shortly after IgM and is a marker of past infection or vaccination.

Supportive care:  - IV fluids if dehydrated or vomiting - Rest as needed - Exclusion from school or work for one week after onset of the illness
Acetaminophen and some other anti-pyretics can potentially cause damage to liver cells, so they should be avoided

HAV immunization are recommended for patients traveling to edemic areas.
Good hygiene, especially in child care centers: handwashing after changing diapers, handwashing before handling food, and heating food to 85 degrees C for >1 minute to inactivate HAV
Families adopting children from endemic areas should have their serostatus checked and get immunized if necessary before the child's arrival. Babysitters and other close contacts of adopted children from endemic areas should also have their serostatus checked and get vaccinated if necessary.
In the hosptial, contact precautions should be used for children in diapers with suspected HAV infection
Post-exposure prophylaxis (PEP): usually recommended after diagnosis of an adult who works at at a child-care center with diapered children. All child care attendees should recieve PEP in that case.  
-For patients <40 years old, a dose of the vaccine given within 2 weeks of exposure is as effective as immunoglobulins 
-Immunoglobulin is recommended for: infants < 1 year of age, individuals with chronic liver disease, and the immunocompromised
Patients with identified cases should not return to work or school for one week after symptom onset. However, if they recieve PEP they may return to school/work immediately.

Routine vaccination of all children (ages 12 to 23 months of age) against HAV has been recommended since 2006.
Two inactivated whole-virus vaccines exist; they are marketed as Havrix and Vaqta. Both require a booster 6 months after the initial dose. Both vaccines are well tolerated, interchangeable, and can be given at the same time as other vaccines. Immunity appears to be long-term (at least 20 years).
There is also a combined HAV-HBV vaccine for patients over 18 years old.

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