Contamination by bacteria and viruses can occur on several levels. In the setting of the laboratory, the growth media, tissues and other preparations used for experimentation can support the growth of unintended and unwanted microorganisms. Their presence can adversely influence the results of the experiments. Outside the laboratory, bacteria and viruses can contaminate drinking water supplies, foodstuffs, and products, causing illness. Infection is another form of contamination.
Equipment and growth media used in the laboratory must often be treated to render them free of microorganisms. Bacteria and viruses can be present in the air, as aerosolized droplets, and can be present on animate surfaces, such as the skin and the mucous membranes of the nasal passage, and on inanimate surfaces, such as the workbenches in the laboratory. Without precautions and the observance of what is known as sterile technique, these microbes can contaminate laboratory growth media, solutions and equipment. This contamination can be inconvenient, necessitating the termination of an experiment. However, if the contamination escapes the notice of the researcher, then the results obtained will be unknowingly marred. Whole avenues of research could be compromised.
Contamination of drinking water by bacteria and viruses has been a concern since antiquity. Inadequate sanitation practices can introduce fecal material into the water. Enteroviruses and fecal bacteria such as Shigella and Escherichia coli O157:H7 are capable of causing debilitating, even life-threatening, diseases. Even in developed countries, contamination of drinking water remains a problem. If a treatment system is not functioning properly, water sources, especially surface sources, are vulnerable to contamination. An example occurred in the summer of 2000 in Walkerton, Ontario, Canada. Contamination of one of the town's wells by Escherichia coli O157:H7 run-off from a cattle operation killed seven people, and sickened over two thousand.
Other products can be contaminated as well. An example is blood and blood products. Those who donate blood might be infected, and the infectious agents can be transmitted to the recipient of the blood or blood product. In the 1970s and 1980s, the Canadian blood supply was contaminated with the viral agents of hepatitis and acquired immunodeficiency syndrome. At that time, tests for these agents were not as sophisticated and as definitive as they are now. The viruses that escaped detection sickened thousands of people. Blood supplies in Canada and elsewhere are now safeguarded from contamination by stringent monitoring programs.
Food products are also prone to contamination. The contamination can originate in the breeding environment. For example, poultry that are grown in crowded conditions are reservoirs of bacterial contamination, particularly with Campylobacter jejuni. Over half of all poultry entering processing plants are contaminated with this bacterium. Other food products can become contaminated during processing, via bacteria that are growing on machinery or in processing solutions. Quality control measures, which monitor critical phases of the process from raw material to finished product, are helpful in pinpointing and eliminating sources of contamination.
With respect to contamination of food, the hygiene of food handlers is a key factor. In the United States, estimates are the one in five food-borne disease outbreaks is caused by the handling of foods by personnel whose hands are contaminated with bacteria or viruses. Poor hand washing following use of the bathroom is the main problem.
In the nineteenth century, similar hygiene problems created a death rate in most surgical procedures. The contamination of open wounds, incisions and entry routes of catheters killed the majority of surgical patients. With the adoption of sterile operating room technique and scrupulous personnel hygiene, the death rate from surgical procedures is now very low.
See also Blood borne infections; Hazard Analysis and Critical Point Program (HAACP); History of public health; Transmission of pathogens