16.2 Routes of Transmission and Blood-Borne Viruses
Key Takeaways
- Transmission in dentistry occurs by direct contact, indirect contact, droplet, airborne aerosol and percutaneous inoculation.
- Standard precautions apply to every patient regardless of known infection status, because most transmissible carriage is undisclosed.
- Transmissibility from a single percutaneous exposure is highest for hepatitis B, intermediate for hepatitis C and lowest for HIV.
- Hepatitis B vaccination with a documented antibody response is an occupational requirement for clinical dental staff and also protects against hepatitis D.
- Endodontic reamers and files are treated as single-use in the UK because prions are not inactivated by standard autoclaving.
The Blueprint Wording
The Paper A blueprint topic is "infection prevention and control of transmission in the oral healthcare setting", and Preparing for Practice outcome 1.1.8 requires registrants to "explain the potential routes of transmission of infectious agents in dental practice, mechanisms for the prevention of infection, the scientific principles of decontamination and disinfection and their relevance to health and safety". Decontamination is only half the topic; the routes themselves are examined directly.
Routes of Transmission in Dentistry
| Route | Mechanism | Dental example |
|---|---|---|
| Direct contact | Contact with blood, saliva or lesion exudate | Herpetic whitlow from an ungloved finger contacting a primary herpetic lesion |
| Indirect contact | Contaminated instruments, surfaces or equipment | Inadequately processed handpiece; contaminated light handle |
| Droplet | Particles above about 5 micrometres travelling short distances and settling | Coughing, sneezing, three-in-one syringe spatter |
| Airborne (aerosol) | Particles below about 5 micrometres remaining suspended and travelling further | Ultrasonic scaler, air turbine, air polisher |
| Percutaneous (sharps) | Inoculation through skin | Needlestick, bur, scaler tip, matrix band |
Aerosol-generating procedures are the reason for rubber dam, high-volume aspiration, pre-procedural mouthrinse and ventilation requirements, and for the personal protective equipment worn during ultrasonic scaling and rotary cutting.
Standard Precautions
Standard (universal) precautions apply to every patient regardless of known infection status, because most transmissible carriage is undisclosed or unknown. They comprise:
- Hand hygiene at the recognised moments, with alcohol gel for socially clean hands and soap and water where hands are visibly soiled or where spore-forming organisms are a concern
- Personal protective equipment appropriate to the procedure — gloves, surgical mask, eye protection for clinician, assistant and patient, and a fluid-repellent gown for aerosol-generating procedures
- Safe handling and disposal of sharps
- Environmental cleaning and management of spillages
- Single-use items used once and discarded, never reprocessed
- Safe management of clinical waste
The Principal Blood-Borne Viruses
| Virus | Approximate transmission risk from a single percutaneous exposure to a positive source | Vaccine | Notes |
|---|---|---|---|
| Hepatitis B (HBV) | Highest of the three, historically quoted as up to about 30% from an e-antigen positive source | Yes | Vaccination with documented anti-HBs response is an occupational requirement for clinical dental staff |
| Hepatitis C (HCV) | Intermediate, historically quoted at around 3% | No | Curable with direct-acting antivirals |
| HIV | Lowest, historically quoted at around 0.3% | No | Post-exposure prophylaxis available |
The ranking — hepatitis B considerably more transmissible than hepatitis C, which is more transmissible than HIV — is the examinable point.
Hepatitis D can only replicate in the presence of hepatitis B, so hepatitis B vaccination also protects against hepatitis D.
Immediate Management of an Inoculation Injury
- Encourage bleeding gently. Do not scrub, suck or squeeze aggressively.
- Wash under running water with soap; irrigate mucosal or conjunctival splashes copiously with water or saline.
- Cover the wound with a waterproof dressing.
- Report immediately under the practice policy and record the incident.
- Risk assess — obtain consent from the source patient for testing where possible; the source patient must never be tested without consent.
- Seek urgent occupational health or emergency department assessment. HIV post-exposure prophylaxis is most effective when started as soon as possible, ideally within two hours, and the window closes at around 72 hours. Hepatitis B immunoglobulin and a booster may also be indicated.
Transmissible Spongiform Encephalopathies
Prions are not inactivated by standard autoclaving. Current UK practice therefore requires that endodontic reamers and files are treated as single-use and that certain instruments used on patients identified as at increased risk of CJD are quarantined or destroyed rather than reprocessed.
Exam link. A stem describing a needlestick from an unknown source is testing the immediate sequence: encourage bleeding, wash, report, and seek urgent assessment within two hours. Waiting for the source result before seeking assessment is the wrong answer, because prophylaxis is time-critical.
Post-Exposure Management in the UK
The immediate management of an inoculation injury follows a fixed sequence that examiners expect verbatim: stop, encourage the wound to bleed gently without scrubbing or sucking, wash with soap and running water, irrigate mucosa and eyes copiously with water or saline, cover the wound, and report the incident immediately. Risk assessment is then carried out urgently — by occupational health in hours, by the emergency department out of hours — considering the depth of injury, the device, whether blood was visible, and the source patient's status.
The timing rules are the examinable detail. HIV post-exposure prophylaxis is most effective when started within hours and is generally not offered beyond 72 hours. Hepatitis B is managed according to the recipient's vaccination and antibody status, with a booster or hepatitis B immunoglobulin as indicated, ideally within 48 hours. Hepatitis C has no vaccine and no post-exposure prophylaxis; management is serological follow-up with early treatment of established infection, which is now curable with direct-acting antivirals. Consent must be obtained from the source patient before testing their blood, and the injured worker must not take that sample themselves.
Registration, Vaccination and Exposure-Prone Procedures
Dentistry is an exposure-prone procedure speciality, so UK registrants must be immune to hepatitis B and must be able to demonstrate it. Healthcare workers who are hepatitis B e-antigen positive, or who have a high hepatitis B viral load, or who are HIV positive and not on effective treatment with a suppressed viral load, or who are hepatitis C RNA positive and untreated, are restricted from exposure-prone procedures until the relevant criteria are met. Registrants have a professional duty under GDC Standards for the Dental Team to seek advice and to act on it if they believe they may be infected — continuing to operate without occupational health advice is a fitness to practise issue, not merely a clinical one.