Cross-infection and sterilization
Cross-infection might be defined as the transmission of infectious agents among patients and staff within a hospital environment. Transmission can occur between individuals by direct contact but it involves fomites, that is, contaminated inanimate objects. In dentistry, the three main sources of infection are: (1) patients suffering from the infectious disease; (2) patients in the prodromal stage of certain infections; and (3) individuals who are carriers of pathogenic microorganisms. It is rare for a patient who is suffering from an acute infectious disease to require dental treatment, although this might occur in an emergency situation. A more likely source of infection is a patient who attends for treatment during the prodromal stage of an infectious disease. At this stage of the infection, the secretions and blood of the patient might be infectious to others, although the patient might appear and feel relatively well. Certain bacterial and viral infections have a prodromal stage, although the phenomenon is more common with viral agents than with bacteria.
Cross-infection may be defined as the transmission of infectious agents among patients and staff within a hospital environment. Transmission can occur between individuals by direct contact but more commonly it involves fomites, i.e. contaminated inanimate objects. In order to understand cross-infection in the dental surgery it is important to have some idea of the source of the infective agents, the means by which they are transmitted, and the route by which they find their way into the tissues of the recipient. In dentistry the three main sources of infection are: (1) patients suffering from the infectious disease; (2) patients in the prodromal stage of certain infections; and (3) individuals who are carriers of pathogenic microorganisms.
It is rare for a patient who is suffering from an acute infectious disease to require dental treatment, although this may occur in an emergency situation. A more likely source of infection is a patient who attends for treatment during the prodromal stage of an infectious disease. At this stage of the infection the secretions and blood of the patient may be infectious to others, although the patient may appear and feel relatively well. Certain bacterial and viral infections have a prodromal stage, although the phenomenon is more common with viral agents (e.g. mumps, measles and chickenpox) than with bacteria. Another group of patients who may be potentially infectious to their dentist during treatment are those who are carriers of various pathogenic agents. There are two types of carriers: (1) convalescent carriers, who have suffered from infections and have apparently recovered but still shed microorganisms into their blood and certain of their secretions; and (2) asymptomatic carriers, who give no past history of infection. To all intents and purposes it is almost impossible for a dentist to diagnose accurately patients who are in the prodromal stage of an infection or those who are carriers. Therefore it makes sense for a dentist to assume that all patients are potentially infectious and to take reasonable precautions to protect both himself and his staff from infection during treatment. In addition, he must ensure that his patients do not become infected during dental treatment in his surgery.
Microorganisms enter the tissues of the recipient by means of injection through intact skin or mucosa (usually due to an accident involving a sharp instrument) or via defects in the skin (for example, recent cuts or abrasions). Another possible route of infection is by inhalation of infected droplets.
Therefore, it is clear that, during treatment in a dental surgery, pathogenic microorganisms could be transmitted both to and from patients and staff in a number of ways. There is little doubt that a number of infections can be transmitted from patient to dentist during treatment by direct contact, e.g. syphilis, by injection, e.g. hepatitis B, and by aerosols, e.g. the common cold or mumps. Similarly, a dentist may infect a patient during treatment by direct contact, e.g. hepatitis B, and by infective aerosols, e.g. tuberculosis or the common cold. The transmission of hepatitis B from a dentist to his patient probably occurs via infected blood from cuts or abrasions on the dentist’s fingers coming into contact with fresh surgical wounds in the patient’s mouth. Compared to a dentist, a dental surgery assistant (DSA) is at considerably less risk of either becoming infected or of transmitting infection to a patient during treatment. However, DSAs may become infected by an accidental penetrating wound during handling of contaminated sharp instruments, or by aerosols if working close to the site of operation when high speed instruments are being used. The dental mechanic is at least risk of infection, with the most likely scenario being an accident involving a contaminated small, sharp clasp on a chrome cobalt denture. Finally, it is the responsibility of the dentist to ensure that the transmission of infection from one patient to another does not occur. This is generally achieved by ensuring that all instruments and equipment are rendered safe for use between patients.
The microorganisms which can be transmitted by infected aerosols are shown in Table 17.1. The majority of these are common viral infections. When aerosols are produced by high-speed instruments, two different types of particles are produced. The characteristics of these are shown in Table 17.2 and, while the smaller particles are involved in transmission by inhalation, the larger particles coat surfaces and may enter the tissues via cuts. The microorganisms involved in transmission by direct contact and by injection are hepatitis B virus, human immunodeficiency virus, herpes simplex virus and Treponema pallidum. Details about the microorganisms involved in cross-infection in dentistry are given in Chapters 8, 10, 15 and 16.
|Diameter||<100 μm||>100 μm|
|Time spent airborne||Minutes||Hours|
|Penetration into respiratory tract||Unlikely||Possible|
|Likely mode of transmission||Direct contact or in dust||Inhalation|
Methods of preventing cross-infection can be conveniently considered under two headings: (1) prevention of infection among staff; and (2) prevention of infection from patient to patient. It is also important to obtain a thorough medical history from patients at their initial visit, and, at subsequent visits, to ask specific questions regarding recent medications, current or recurrent illnesses, lymphadenopathy, unintentional weight loss, oral soft-tissue lesions and a past history of jaundice.
A list of the vaccines available for health care staff are shown in Table 17.3. Staff who have no natural or acquired immunity to these infections should be immunized by their general medical practitioner.