Reports of hepatitis A infections in the United States increased by about 300 percent in 2016-2018 compared with the previous two years, according to research published this week by the Centers for Disease Control ad Prevention.

A significant percentage of the confirmed patients in 2016-2018 were infected by contaminated food, according to the research team led by Dr. Monique A. Foster of the Division of Viral Hepatitis at the National Center for HIV, Viral Hepatitis, STD, and TB Prevention of the CDC.

In the past two years, Food Safety News has reported public health officials in some states have said 20 percent to 30 percent of the confirmed hepatitis A patients they have recorded were not in any of the so-called high risk groups, which suggests they became infected through contaminated foods or beverages.

The 294 percent nationwide increase logged by public health officials in the past two years shows the need for protection for unvaccinated adults, as well as the need for ongoing vaccination programs for children, according to the research published in the CDC’s Mortality and Morbidity Weekly Report.

“Rates of hepatitis A had declined by approximately 95 percent during 1996-2011,” according to the report. “However, during 2016-2018, CDC received approximately 15,000 reports of HAV infections from U.S. states and territories, indicating a recent increase in transmission.”

Two of the largest food-related hepatitis A outbreaks in the past two years involved imported, frozen raw scallops served at Genki Sushi fast food restaurants in Hawaii and imported frozen strawberries served by Tropical Smoothie Cafe locations, mostly along the East Coast. The scallops were from Vietnam and the strawberries were from Egypt.

The Food and Drug Administration this week announced it had begun a special testing program on frozen strawberries, raspberries and blackberries from domestic and foreign sources. The agency is collecting 2,000 samples that will be tested for norovirus and hepatitis A.

According to the research published this week, nine U.S. states and Washington D.C. had an increase of about 500 percent in hepatitis A case counts during 2016-2018 compared with 2013–2015. Eighteen U.S. states had lower hepatitis A case counts.

“In the past, outbreaks of hepatitis A virus infections occurred every 10-15 years and were associated with asymptomatic children,” according to the report. “With the widespread adoption of universal childhood vaccination recommendations, asymptomatic children are no longer the main drivers of hepatitis A outbreaks.

“… Decreasing new infections from hepatitis A virus can be achieved and sustained by maintaining a high level of population immunity through vaccination.”

The researchers reported a large population of susceptible, unvaccinated adults who were not infected by being exposed to the virus during childhood remain vulnerable to infection by contaminated foods and other sources. The majority of people reported infected by the hepatitis A virus in 2016-2018 were either homeless, and substance abusers, or both.

Although the research report didn’t specifically identify foodservice workers — such as restaurant employees and people working in school and hospital cafeterias — as one of the groups that should be vaccinated, some public health advocates have called for industry and government to pursue vaccination programs for those people.

Reports from public health agencies about infected foodservice workers have come on almost a daily basis since 2016. People can be infected by the virus and never exhibit symptoms. Others who do develop symptoms are able to spread the virus for several days before becoming sick. It can take up to 50 days for symptoms to develop. 

Sometimes the infected employees are identified quick enough for restaurant and cafeteria patrons to seek post-exposure vaccinations. However, there is only a two-week window of opportunity after exposure when such treatment is effective.

In addition to Foster, researchers who worked on the project included Megan G. Hofmeister, Benjamin A. Kupronis, Yulin Lin, Guo-Liang Xia, Shaoman Yin, and Eyasu Teshale.