Chris Miller, PHD
The two basic approaches to the prevention of infectious disease are, first, reducing or preventing exposure to microbes and, secondly, enhancing the body`s resistance to microbes.
The first approach of containing microbial exposure is referred to as infection control or exposure control. This approach involves battling the microbes before they enter the body. The second approach of enhancing the body`s resistance involves immunizations and prophylactic antimicrobial agents. This approach involves battling microbes after they enter the body.
An infectious disease occurs when a microbe of sufficient virulence enters the body through the appropriate route, multiplies to a level that overwhelms body defenses, and causes damage to some part of the body. From this description, one can identify the important aspects of disease development:
* The microbe first must have sufficient virulence (ability to produce disease). Virulence comes from several potential properties including:
- The ability to evade body defenses
- The ability to produce harmful substances that destroy or change our body cells
- The ability to suppress our body defense systems
* Secondly, the microbe must enter the body through a route that will permit its survival and support its multiplication.
* Thirdly, the microbe must multiply to some level that at least begins to challenge the body defenses and possibly overwhelm the defenses locally or systemically.
* Fourth, the microbe expresses its virulence properties, causing damage to the body.
We recover from infectious diseases when body defenses win the battle with the microbe and reduce it to harmless levels. Recovery also occurs when administered antimicrobial agents reduce the level of microbes to a point that permits the body defenses to eliminate the rest.
The goal of infection control is to reduce the number of microbes that contact the body. It makes perfect sense to keep this dose of microbes as low as possible. The fewer microbes that contact the body, the fewer that will be there to enter the body, the fewer that will be there to multiply, and the fewer that will need to be eliminated by the body defenses. Reducing this dose through infection control will give the body the best chance to prevent a disease from occurring by allowing the body to battle a lower level rather than a higher level of microbes.
We will never be able to keep all microbes from contacting the body, for we are continually being bombarded with microbes from the environment and from our normal contacts with humans, animals, and insects. However, we can take certain precautions to reduce this dose, especially when:
- Potentially virulent (pathogenic) microbes may be involved
- The potential for entrance of microbes into the body may be enhanced
- The body`s resistance may be low.
Unfortunately, we don`t always know when one may be exposed to potentially virulent microbes. For example, we never know the exact composition of a source of microbes involved in a contamination involving an environmental surface, saliva, blood, or dental unit water, air, or skin. Also, we don`t always know when the entrance of microbes into the body may be enhanced through unrecognized breaks in the skin or mucous membranes. Likewise, we don`t always know when one`s resistance to a given microbe may be low. All of these unknowns tend to foster a certain level of "overkill" in infection control that is reflected in the saying, "Better to be safe than sorry."
Filling the gaps in evidence
While we must always strive to practice evidence-based infection control (having scientific evidence to back up the need for a specific infection control procedure), the evidence may not always be as strong as we would like. One of the biggest gaps in our infection control knowledge is knowing the risk of acquiring an infectious disease in a given situation. If such risks are known, they help justify the importance of, or need for, a particular infection control procedure.
There are two aspects to consider with such risks. One is the risk of cross-contamination (the transfer of microbes from one person to another). The other risk is cross-infection (the occurrence of infection following cross-contamination).
If there is evidence for cross-infection, then one knows that cross-contamination had to occur. Likewise, if cross- contamination occurs, there is some potential for cross-infection. We all would like to have cross-infection evidence as the basis for using a given infection control procedure. For example, the evidence for the involvement of sharps injuries in cross-infection of bloodborne diseases provides a solid and unquestioned foundation for using infection-control procedures to prevent sharps injuries among health-care workers.
Unfortunately, we do not have such strong evidence to support all of infection control. So we also must rely upon cross-contamination data that, at least, establishes some degree of potential for cross-infection. For example, while less information exists about cross-infection in dentistry involving ungloved hands, dental aerosols, contaminated dental unit water, or contaminated dental operatory surfaces, it is clear that all of these involve cross-contamination and, therefore, some potential for cross-infection.
Since we cannot predict all situations that will cause a cross-contamination to result in a cross-infection, a certain amount of overkill is built in to infection control to assure the best protection for patients and dental personnel. Performing infection control to reduce cross-contamination gives the body a better chance to defend itself against disease agents.
Chris Miller is director of Infection Control Research and Services and professor of oral biology at Indiana University.