Food borne disease are caused by low-dose pathogens and may be considered to differ from food poisoning in that:
Viruses are present in the vomit of ill persons and viral gastroenteritis is primarily spread by airborne infection, environmental contamination and fro person to person. Re-infection frequently occurs. Outbreaks involving children and closed communities are common, for example, nurseries, nursing homes, schools and cruises.
Noroviruses are the major cause of viral food borne cases and outbreaks in the UK. The on set period is 10 to 50 hours, but usually around 24 to 48 hours, and is does dependent. The ineffective does is very low, between 10 and 100 organisms. Symptoms include vomiting (the predominant symptom and usually projectile), some diarrhoea, abdominal pain, fever and nausea. Symptoms usually last around 12 to 60 hours and patients are infectious for a further two days.
Viruses are around 3/100ths the size of bacteria and can only be seen through an electron microscope. They multiply in living cells not food. Transmission depend on contamination of food by food handlers or sewerage. Filter feeding bivalves, such as oysters harvested from sewerage-polluted waters, are a major problem. Foods which are handled the most present the greatest risk; ice, desserts, cold meats, salads and some fruits are frequently involved, but the vehicle is rarely identified.
Viruses thrive in cold conditions and are destroyed at temperatures above 60°C. Relaying of shellfish in clean water is ineffective against viral contamination.
Control measures include staff training, the exclusion of ill food handlers,the implantation of HACCP, effective cleaning and disinfection of surfaces and equipment, the use of reputable suppliers and the washing/ blanching of fruit and salads.