Food Safety Focus (203rd Issue, June 2023)–Article 2

Hepatitis A and Frozen Strawberries

Reported by Mr. Arthur YAU, Scientific Officer,
Risk Communication Section, Centre for Food Safety

Since late March 2023, the United States has reported outbreaks of hepatitis A linked to the consumption of contaminated frozen ready-to-eat strawberries from certain farms in Mexico. Nine cases were found across different states and three people required hospitalisation. The incriminated frozen strawberries were recalled as a result. Investigation revealed that the strawberries were from the same suppliers and farms which had also caused another hepatitis A outbreak in the United States earlier last year. Similar outbreaks of hepatitis A associated with frozen ready-to-eat berries had been reported in the past.

What is Hepatitis A and How Does It Spread?

Hepatitis A virus (HAV) is the agent that causes hepatitis A, leading to inflammation of the liver. Mild symptoms like fever, loss of appetite, nausea, vomiting, diarrhoea, muscle aches and yellowing of eyes and skin (jaundice) usually appear within two to four weeks after consuming contaminated food or drinks, and often last for a week or two. Sometimes HAV infections can be asymptomatic, especially in children. The infection is usually self-limiting and most people will recover on their own and develop immunity as a result. On rare occasions, this illness can quickly cause severe liver damage and death, which is more common in the elderly or people with chronic diseases.

Humans and certain primates are the only natural hosts to HAV. The virus mostly spreads through the faecal-oral route; that is when a person ingests food which has been directly or indirectly contaminated with the faeces of an infected person (Figure 3). Food can be contaminated by dirty hands of an infected person, water for irrigation or washing and in some extent via contaminated utensils and pests like flies. Raw fruits and vegetables, shellfish, ice and drinking water are common food sources of HAV. Only a very small number, as low as 10 to 100, of HAV particles is necessary to cause an infection. HAV can survive at cooking temperatures that would otherwise kill other pathogens in food (e.g. 75°C for 30 seconds), freezing, drying, common household chemicals or on dry surfaces for hours.

Figure 3: Transmission routes of HAV and common symptoms of hepatitis A

Why is HAV Capable of Easily Causing Foodborne Outbreaks?

The HAV can spread through food efficiently. Furthermore, when infected food handlers do not wash their hands properly after using washrooms, they can spread the HAV to food and the utensils they touch. In some parts of the world where there is inadequate treatment of human waste, the HAV from stools can contaminate drinking and irrigation water. This is especially an issue for produce like berries that are consumed raw and are too fragile to be cleaned thoroughly. When mass-produced food is exported in bulk worldwide, the HAV can also spread across different parts of the world.

Berries and other produce can be contaminated with the HAV at different stages of production, such as when they are irrigated, processed or washed with contaminated water, or when they are handled by people with hepatitis A who have not washed their hands. Furthermore, because these products require a lot of water and handling during processing, it is no surprise that outbreaks like these have happened all over the world, often in countries with low hepatitis A prevalence.

How to Prevent the Spread of HAV in Food

Water for irrigation, cleaning and food processing should be clean. Visitors to farms should maintain good hygiene and adequate means of hand sanitation should be provided.

All people, especially food handlers, should wash their hands properly after using washrooms, before eating, before preparing food and after touching raw foods and unclean objects. Always follow the Five Keys to Food Safety – choose (choose safe raw materials); clean (keep hands, utensils and working environment clean); separate (separate raw and cooked food); cook (cook thoroughly to a more stringent 90°C for 90 seconds for the HAV); and safe temperature (keep food at safe temperatures) to prevent foodborne diseases.

Food handlers may consider receiving hepatitis A vaccines to prevent infections. Those who are experiencing symptoms of HAV infection should refrain from handling food and seek medical attention immediately.