Spoilage We See and Smell

• Many spoilage microorganisms advertise their presence in moldy fruit and vegetables, discolored meat and soured milk. When we can see and smell the evidence, the affected foods are unlikely to harm us because they go straight into the garbage. Oxygen, alone or in combination with moisture and bacteria, works with naturally occurring enzymes in foods to initiate chemical reactions that produce obvious spoilage. Heat accelerates this process, which is why we store perishable foods in refrigerators and freezers. However, microorganisms that alter the color and smell of foods aren't nearly as hazardous as those that produce no changes we can see, smell or taste.

Invisible Threats

• Hundreds of disease-causing viruses, bacteria and parasites and the toxins generated by them don't signal their presence in any way our senses can detect. The Institute of Food Technologists says more than 200 food-related diseases are known to be caused by such pathogens. The names of a few are familiar to most people: E. coli, salmonella, listeria and botulism. But the pathogens responsible for causing more than half of all food poisoning outbreaks in the U.S. are never identified, suggesting to the IFT that 200 or more others are active but flying below the regulatory radar.

Numbers Versus Severity: Two Extremes

• From a public health perspective, identifying the "worst" pathogens depends upon how you define that word. Going by numbers alone, norovirus, also known as Norwalk virus and the most common cause of food poisoning, would win hands down. According to the CDC, norovirus sickens 19 to 21 million Americans every year, helping to place 56,000 to 71,000 people in the hospital and kill 570 to 800 people. Therefore, even at its most virulent, norovirus is fatal in only 0.004 percent of cases. At the other extreme is Vibrio vulnificus, a relatively rare disease contracted from eating raw seafood, especially oysters. On average, V. vulnificus affects 95 Americans annually, resulting in 85 hospitalizations and 35 deaths -- a fatality rate of 37 percent.

People at Highest Risk

• Anyone who eats spoiled or contaminated food can come down with food poisoning, but the health consequences for some groups are more dire than others. For example, listeria seldom results in more than a little queasiness among healthy children and adults, but in pregnant women, it can cause miscarriage, stillbirth and the death of newborns. In general, pregnant women, older adults and people with conditions that weaken the immune system, including AIDS, cancer and diabetes, are at higher risk of serious or life-threatening illness from foodborne pathogens.

Keeping Food Safe

• Many foodborne pathogens are neutralized by heat, so thorough cooking, including checking the interior temperatures of meat with a meat thermometer, eliminates those risks. When handling food, wash your hands with soap and water frequently, especially after you've touched raw meat, fish or poultry. Wash produce under running water. Counters, cutting boards and utensils should be washed before reuse if they've come into contact with raw meat. Pay attention to expiration dates, especially on prepared foods such as mayonnaise, and discard foods when they're past their prime. When in doubt, throw it out. Don't leave perishable foods unrefrigerated for longer than two hours.