Viruses are also microscopic, but are not actually live cells. Viruses need to combine with a live cell where they act sort of like a parasite, taking over the cell and changing its nature and function to something harmful. They are likely to get into food in similar ways to bacteria and can affect any food type. They don't multiply in food they just use the food as a vehicle to get around.
Some of the viruses common to food borne illness in New Zealand include:
- Rotavirus These can cause fever, vomiting and watery diarrhoea starting 24 - 72 hours after consumption lasting 4 - 6 days.
- Norwalk These can cause nausea, vomiting, diarrhoea, abdominal pain, muscle pain and headache, fever and general malaise starting 10 - 50 hours after consumption lasting 24 - 48 hours.
- Hepatitis A You will note that viral illness tends to show itself faster than many bacteria, much like a toxin, or food poisoning. They also tend to last longer and are more severe. It is believed that many food borne viral illness go unidentified as such and that viral contamination of food is becoming much more prevalent than it used to be. It is therefore even more important for premise cleaning and personal hygiene measures to be used thoroughly, stringently and frequently.
Metallic compounds are naturally present in many foods in low concentrations which are not harmful. But some excessive amounts get into foods via herbicidal, antifungal and insecticidal sprays of fruit and vegetables, plumbing pipes for drinking water reticulation or from ceramic glazing, tin can coatings or trade waste contaminated waters in which seafood are harvested.
Some metals which can become food contaminants in these ways include:
- Antimony and cadmium
Some other food borne chemical contaminations include arsenic, selenium sodium nitrite, from meat pickling, algae toxins and some other pesticides. Your local Health Protection Officers from the Ministry of Health will periodically sample foods at the point of processing, and recreational waters, to test for harmful levels of these contaminants to ensure the Food Regulations (or new ANZFA regulations) are not breached.
To help prevent illness from chemicals and metals you must ensure that:
- all fruit and vegetables are thoroughly washed prior to use,
- all metal cook ware and utensils are of high quality and in good condition,
- you use a council supplied water source (as opposed to a private one) so that the water will be tested for chemical and metals,
- do not use crockery that has been imported without customs and MAF checking to ensure the glazes are safe to eat from,
- you must be particularly careful with the storage of acidic foods as these can cause leaching of the metal from the container.
- you must also be sure that any shellfish have been harvested from proven safe waters
- and that any pickled meats you purchase have come from licensed butchers to ensure that their pickling solutions are of the correct concentrations.
All the remaining sections of this text combine to show you how to prevent food borne illness. Contamination is an aspect of food safety that there is no excuse for. What is not already there naturally must not be allowed to get there, and what is there naturally must be controlled. Knowledge of the risks associated with different food types will help you decide how to treat each food item you deal with and prevent the three different types of contamination at all times.