ESSENTIALS OF DIAGNOSIS
Prodrome of anorexia, nausea, vomiting, malaise, aversion to smoking.
Fever, enlarged and tender liver, jaundice.
Normal to low white cell count; markedly elevated aminotransferases.
Hepatitis can be caused by viruses, including the five hepatotropic viruses—A, B, C, D, and E—and many drugs and toxic agents; the clinical manifestations may be similar regardless of cause. Hepatitis A virus (HAV) is a 27-nm RNA hepatovirus (in the picornavirus family) that causes epidemics or sporadic cases of hepatitis. HAV infection is hyperendemic in developing countries. Globally, over 1.5 million people are infected with HAV annually. The virus is transmitted by the fecal-oral route by either person-to-person contact or ingestion of contaminated food or water, and its spread is favored by crowding and poor sanitation. Since introduction of the HAV vaccine in the United States in 1995, the incidence rate of HAV infection has declined from as much as 14 to 0.4 per 100,000 population, with a corresponding decline in the mortality rate from 0.1 to 0.02 deaths per 100,000 population and an increase in the mean age of infection and death. Nevertheless, over 80% of persons aged 20–60 years in the United States are still susceptible to HAV, and vulnerable populations are especially at risk. The highest incidence rate (2.1 per 100,000) is in adults aged 30–39. Common source outbreaks resulting from contaminated food, including inadequately cooked shellfish, or untreated ground water from wells continue to occur, although no drinking water–associated outbreaks have occurred in the United States since 2009. In 2017, an outbreak beginning in California and extending to at least 33 other states affected a large number of homeless persons and resulted in many deaths. In addition to homeless persons, outbreaks may occur among people who inject drugs or unvaccinated residents in institutions and among men who have sex with men and among international adoptees and their contacts. In the United States, international travel emerged as an important risk factor, accounting for more than 40% of cases in the early 2000s but a lower percentage in the 2010s. Overall, reports of HAV infection increased by nearly 300% during 2016–2018 compared with 2013–2015.
The incubation period averages 30 days. HAV is excreted in feces for up to 2 weeks before clinical illness but rarely after the first week of illness. The mortality rate for hepatitis A is low, and acute liver failure due to hepatitis A is uncommon except for rare instances in which it occurs in a patient with concomitant chronic hepatitis C. There is no chronic carrier state. In the United States, about 30% of the population have serologic evidence of previous HAV infection.
Figure 18–1 shows the typical course of acute hepatitis A. Clinical illness is more severe in adults than in children, ...