Hand washing before sitting for the food is a basic tenet inculcated even at young age because of the underlying principle that cleaning removes dangerous disease causing bacteria and other harmful materials preventing their access to the stomach. There are many pathogens that can cause minor stomach upset and some times serious gastroenteritis. Even hand washing is mired in controversy though many believe that thorough washing using soap suds can remove most, if not all, harmful bacteria from hands. The efficiency of washing is a function of quantity of water used and thoroughness with which hands are rubbed against each other. Use of antiseptic hand wash preparations often leave behind significant counts of bacteria leaving no alternative to washing under profuse running water. The disturbing question that keeps coming back when hand washing is considered pertains to water shortage being experienced in many developing countries making it impractical to expect people to use the required water for thorough cleaning before touching the food. The problem is very acute in countries where food is eaten with bare hands unlike westerners who use spoons and forks.
Another dimension to food safety is posed by the need to store foods for some time and it is very common for people to store prepared foods for at least a few hours, especially when excess foods are prepared, for consuming later. Of course refrigerators do help to control the density of microbial colonies because bacterial growth is temperature sensitive. But how many households in India or other developing countries have access to refrigerators? Very few families belonging to middle and upper class income group can afford the luxury of refrigerators and foods will have to remain under ambient conditions for a few hours before actual consumption. Even when refrigerators are available, house wives rarely shove the food into refrigerator under the mistaken impression that it is safe for few hours. Unfortunately the bacteria can grow exponentially if the initial contamination level is high, especially in foods rich in nutrients. Some of the serious contaminants which have caused havoc recently include Staphylococcus aureus, Clostridium perfringens, Listeria monocytogenes and Escherichia coli O157;H7
There is an impression that bacteria pose danger only in nutrient rich foods like meat, fish, poultry etc which are considered highly perishable and most incidences of food poisoning occur in this category of foods. But the belief that other foods are not vulnerable is a fallacy as reflected by a series of food poisoning episodes involving such innocuous materials like spinach, tomato, lettuce, peanuts, walnuts etc. Improper handling and storage can make any food vulnerable to contamination and adequate precaution must be taken to preempt such incidences. According to microbiological experts all foods are risky to be exposed to a bacterial "danger zone" when temperatures are between 5C and 60C enabling these bugs to multiply rapidly. It is not exaggeration when a microbiologist states that every single bacterial cell can multiply within half an hour reaching several millions in less than 12 hours!.One can imagine the consequences of the presence of such high levels of bacteria in foods, especially if they are pathogenic!.
What about reheating? Does it help to make the old food safe? It depends on the nature of food and extent of heating. Cold foods such as salads are not fit to be heated while cooked foods cannot be reheated to kill all the contaminants without compromising on the eating quality. The composition of food also makes a difference. While high salt or sugar or acidic foods are relatively safer, others with normal composition and taste can pose safety risks of higher order. As a thumb rule experts believe that if cooked food is to be preserved for a few hours, it must be refrigerated under 4C or reheated to at least to 75C before consumption to be safer.