Norovirus is the leading cause of acute gastroenteritis worldwide, responsible for an estimated 50% of all foodborne outbreaks. It is highly infectious, with an infectious dose as low as 10-100 viral particles. Transmission occurs via the fecal-oral route, contaminated food (particularly shellfish from polluted waters, fresh produce, and ready-to-eat foods handled by infected workers), person-to-person contact, and contaminated surfaces. The incubation period is 12-48 hours, with symptoms of vomiting, diarrhea, nausea, and abdominal cramps lasting 24-72 hours. Immunity is short-lived, and reinfection with different genotypes is common.
Hepatitis A virus (HAV) causes inflammation of the liver with a much longer incubation period of 15-50 days (average 28 days). Symptoms include jaundice, dark urine, fever, fatigue, and abdominal pain. Unlike norovirus, hepatitis A infection confers lifelong immunity. HAV is transmitted through contaminated food and water, with outbreaks linked to frozen berries, green onions, pomegranate arils, and bivalve shellfish. A vaccine is available and is recommended for travelers to endemic areas and food handlers in some jurisdictions.
Detection of enteric viruses in food relies on reverse transcription quantitative PCR (RT-qPCR). For norovirus and HAV in shellfish, the ISO 15216 standard method specifies virus extraction from digestive tissue followed by RT-qPCR. Detection in produce and water uses polyethylene glycol precipitation or ultrafiltration for concentration. Interpretation of positive results must account for the inability of RT-qPCR to distinguish infectious from non-infectious virus. Alternative methods such as viability PCR (using intercalating dyes like PMAxx) and cell culture (for HAV, using FRhK-4 cells) can assess infectivity.
Prevention relies on strict hand hygiene (alcohol-based sanitizers are less effective against norovirus; hand washing with soap and water is critical), exclusion of ill food handlers for at least 48 hours after symptom resolution, thorough cooking of shellfish (internal temperature >90°C for 90 seconds), and sanitation of food contact surfaces with chlorine-based disinfectants. HAV vaccination of food handlers is recommended in some countries. Improved water quality management and virus monitoring in shellfish growing areas are essential for primary prevention. Viral pathogens cause food infection rather than intoxication. Unlike bacterial pathogens such as Salmonella, viruses do not replicate in food. Prevention relies on hand hygiene and HACCP-based controls.
