Retrograde contamination – causes and solutions

Retrograde contamination generally refers to contamination in a direction opposing the direction of flow. This occurs when water outlets (e.g. taps and shower heads) come into contact with microbes as a result of splashback of water. The risk is greatest where splashback from the plug hole is concerned; this can lead to retrograde contamination from the waste trap. For this reason the stream of water should not fall directly into the plug hole.

If the water system is infected with microbes, water filters are installed immediately to stop these microbes effectively. But water filters are at risk of retrograde contamination as well. There are several different ways to keep this risk to a minimum.

For example, a bacteriostatic additive in the plastic of the filter housing prevents the growth of microbes. Bacteriostatic additives dock on at a point in the biosynthesis of proteins, in which the DNA is translated in successive steps into an amino acid sequence. The additives thus block this essential part of the regeneration of an organism. It is also possible for water outlets to be coated with a bactericidal material which actively kills microbes. Because of their bactericidal action, silver and copper are among the substances that have proven suitable for coating water outlets.


It is very important to handle water filters correctly


However, as well as protecting the water filters with bacteriostatic materials, it is also very important to handle them correctly.

  • The filter should not be touched if at all possible.
  • The filter outlet should not come into contact with waste water or non-potable water.
  • Filters should not be cleaned with cleaning agents or a cloth.
  • If a filter becomes visibly contaminated with substances such as blood or mucus, it should be changed immediately.
  • If the filter is visibly damaged it should also be changed immediately.
  • People in establishments equipped with filters must be thoroughly informed about working with medical devices.

To counteract retrograde contamination, it is important to replace filters regularly in accordance with the maker’s instructions. If a filter is used correctly, the risk of retrograde contamination occurring within the indicated service life is minimal. Medical products go through various groups of tests for validation. To assess the risk of retrograde contamination, water containing microbes is sprayed through the outlet into the filter housing to create retrograde contamination artificially. The filters are then examined during the testing period to detect temporary contamination and persistent microbial colonisation.

Retrograde contamination in dental practices

Dental practices are subject to an increased risk of retrograde contamination of the dental instruments by saliva, blood or wound secretions. These substances travel via the equipment into the water lines. The consequence is that the next patient receives contaminated water, even though there are no biofilms in the pipes of the treatment unit and no microbes in the water originally supplied. Aerosols from suction equipment can also infect open water systems. Appropriate procedures must be put in place so that the patients are not exposed to a risk of infection due to potential retrograde contamination. The Robert Koch Institute makes certain recommendations, including flushing water systems for 20 seconds after each patient. Suitable valves should also be used to inhibit reverse suction and prevent fluids from flowing backwards.