A man carries a net containing shellfish in Saint Malo, France, in 2015. The scallops linked to a Hepatitis A outbreak in Hawaii were imported from the Philippines.Stephane Mahe / Reuters

The Hawaii State Health Department ordered the immediate closure of nearly a dozen locations of the restaurant chain Genki Sushi on the islands of Oahu and Kauai amid the state’s worst Hepatitis-A outbreak in decades.

Officials have confirmed 168 cases of the virus since June, including dozens of people who required hospitalization, saying imported frozen scallops served raw at Genki Sushi are likely to blame. The scallops were imported from the Philippines, according to the Honolulu Star-Advertiser, and distributed by the Honolulu-based wholesale company Koha Oriental Foods.

A Hepatitis-A outbreak of this scale is unusual but not unprecedented in recent decades. In 2003, 565 people were sickened in Pennsylvania after eating contaminated green onions at a Chi-Chi’s Mexican restaurant. Three people died as a result. That same year, 297 cases of Hepatitis  A recorded in Georgia were also linked to contaminated green onions. In 2013, 162 people across 10 states got Hepatitis A after eating products containing tainted pomegranate seeds.

Still, the incidence of the virus has dropped dramatically—by some 95 percent—in the United States since a vaccine became available 20 years ago, according to the Centers for Disease Control and Prevention. The CDC recommends vaccinating children at 1 year old, but officials believe many adolescents and adults remain unvaccinated, which is part of why outbreaks like the one in Hawaii are concerning. Hepatitis A is rarely fatal, though it can cause fatal liver failure.

The virus, which sickens those who consume contaminated food or water, is highly contagious and spreads fastest in settings where personal hygiene is subpar or sanitary conditions are poor. Those who are infected stay contagious for up to two weeks, and are often most contagious before symptoms ever appear. It can take several weeks—in some cases even months—after an infection before symptoms show up, making the risk of spreading the virus even greater. Many people who get the virus never show symptoms. In young children, the vast majority of Hepatitis A infections are asymptomatic. Signs of Hepatitis, when they appear, can include fever, fatigue, loss of appetite, abdominal pain, clay-colored bowel movements, vomiting, diarrhea, and yellowing skin and eyes.

Along with closing Genki Sushi for clean-up, the Hawaii State Department of Health also issued a list of establishments where food service workers sickened in the latest outbreak are employed—including Baskin-Robbins, Chili’s, Costco Bakery, Taco Bell, Papa John’s, and several local restaurants on Oahu. This information is important, as Hepatitis A is often spread by food handlers who are themselves infected.

State officials told the Star-Advertiser that they’re working with the U.S. Food and Drug Administration to further investigate the origin of the tainted scallops. Raw shellfish are considered particularly risky for spreading Hepatitis A, since shellfish make efficient filters for extracting bacteria from water—making them great receptacles for the virus when they’re exposed to it. Although many states have regulations aimed at preventing the distribution of contaminated shellfish in the United States, researchers have linked several outbreaks to the illegal harvesting of oysters and scallops. The lesson here, health officials say, is not to eat raw shellfish.

Then again, Hepatitis A is unpredictable, which is part of what makes outbreaks so disconcerting. Going back to the 1960s, major outbreaks of the virus have been traced back to frozen strawberries, frozen raspberries, lettuce, sandwiches, salads, glazed doughnuts, and pastry icing.

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