(CNN)An outbreak of hepatitis A caused by imported frozen strawberries from Egypt has sickened 55 people in six states, the US Centers for Disease Control and Prevention said Wednesday. Health authorities confirmed 44 total infections in Virginia, where the outbreak first appeared, and additional infections in Maryland (4), West Virginia (4), North Carolina (1), Oregon (1) and Wisconsin (1).
Hepatitis A is a viral liver infection that is highly contagious but does not result in chronic infection.
"Due to the relatively long incubation period for hepatitis A -- 15 to 50 days -- before people start experiencing symptoms, we expect to see more ill people reported in this outbreak," CDC spokeswoman Nora Spencer-Loveall said.
About half of the 44 infected Virginians have been hospitalized, according to that state's department of health
. They range in age from 15 to 68. Their symptoms began in early May through August, but health authorities did not develop the theory of a common source of infection until this month.
The Virginia Department of Health originally connected the infection to smoothies, which contained the imported berries, served at Tropical Smoothie Café restaurants.
Almost all those who became sick purchased smoothies at cafés in a limited region including Virginia and neighboring states, reported the CDC. The one ill person in Oregon had traveled to Virginia.
According to the CDC, there are between 1,700 and 2,800 cases of the highly contagious virus each year in the United States. Hepatitis A is spread from person to person. The most common way the virus is transmitted is when someone eats something that has been contaminated with the feces of an infected person, according to the CDC
Though the classic symptom is jaundice -- a yellowing of the skin or the eyes -- other signs include fever, fatigue, loss of appetite, nausea, vomiting, abdominal pain, dark urine and light-colored stools.
"On August 5, the Virginia Department of Health contacted us about a potential link between hepatitis A cases and frozen strawberries from Egypt," Mike Rotondo, CEO of Tropical Smoothie Café, said in a video
posted August 21 on YouTube. He added that the company immediately removed the imported strawberries from its cafes and purchased new strawberries from alternate sources.
The Virginia Department of Health also announced its investigation of the outbreak on August 21. The department said at the time that genetic tests showed the illnesses to be caused by a strain of hepatitis A virus associated with past outbreaks resulting from strawberries imported from Egypt. On Friday, Virginia health authorities confirmed the link between the Egyptian fruit and local infections.
The majority of children who become infected with hepatitis A show no signs of illness, according to the CDC, though more than 80% of adults will experience symptoms. Once recovered from their illnesses, patients are protected against reinfection for life.
Hepatitis A rates in the United States have declined by 95% since a vaccine became available in 1995, according to the CDC. Its most recent data, from 2014, showed a total of 1,239 cases for all 50 states, a 30.4% decrease from the previous year.
The European Center for Disease Prevention and Control
(PDF) reported 15 confirmed cases of hepatitis A infections and 89 probable cases in 14 countries between November 1, 2012, and April 30, 2013. All 104 of these cases were linked to travel to Egypt.
The CDC, the Food and Drug Administration, and several state departments of health are continuing to investigate the outbreak.