Risk profile from noroviruses in green leafy vegetables in Croatia

Noroviruses are nowadays considered one of the most important cause of nonbacterial gastroenteritis in the world. Norovirus genus includes genetically highly diverse group of viruses which belong to different genogroups. To date, 6 norovirus genogroups are discovered, three of which are infectious for humans. GII.4 strain of norovirus predominate among human infections. Symptoms of the disease usually appear 48 hours after exposure to the virus, and are characterized by watery diarrhea, with no traces of blood, and vomiting. Due to the high resistance to environmental conditions, resistance to most commonly used disinfectants and low infectious dose, noroviruses can be transmitted through a variety of modes. The primary mode of transmission, after the outbreak of gastroenteritis, is the fecal-oral route. Noroviruses are usually transmitted directly by contact with an infected person, but they can be transmitted by indirect pathways as well. Indirect pathways include ingestion of contaminated food or water, and contact with contaminated surfaces. Contamination of food with norovirus can occur at any stage of production, including manipulation of food by infected persons in case when food will not undergo sufficient heat treatment afterwards. The most common, and perhaps the best investigated, sources of infection norovirus are shellfish, strawberries, leafy greens and water. Contaminated water represents a direct risk of norovirus infection if used for drinking, or represents a significant danger if used for irrigation of crops or during processing and preparing food. Also, food handlers can transmit the virus through direct contact with food. This is usually the case with infected people or asymptomatic carriers. In order to reduce the risk of norovirus contamination, it is necessary to avoid the use of contaminated water at all stages of the food supply chain. Also, it is necessary to comply with the hygiene requirements, especially hand hygiene and hygiene of food handlers. The implementation of existing prevention programs, such as good agricultural practices, good manufacturing practices and good hygiene practice, should be the primary objective of farmers. By implementation of above mentioned programs along the entire food chain it is possible to control a range of different microbiological hazards.
Croatian Food Agency carried out a study in which samples of fresh lettuce (packaged and unpackaged) were analyzed for the presence of GI and GII genogroups of norovirus. The results showed that none of the 50 samples of lettuce, present on the Croatian market, was contaminated by norovirus. Considering the results of contamination of green leafy vegetables and officially registered number of people suffering from diseases caused by norovirus, the risk of norovirus from green leafy vegetables in Croatia can be considered negligible.
Keywords: norovirus, food, lettuce, prevention, contamination.