When are additional (transmission-based) infection control measures necessary? Standard precautions are designed to protect patients and healthcare workers from not only bloodborne pathogens, but those spread by: (1) blood or all body fluids, (2) excretions or secretions (except sweat) regardless of whether they contain blood, (3) nonintact skin, and (4) mucous membranes.¹  

Under ordinary circumstances, standard precautions have been shown to keep patients and workers safe.²  At times, however, these precautions do not provide sufficient protection against infection, and other steps must be taken in addition to standard precautions based on disease transmission and degree of infection. Such steps are called “transmission-based precautions” and include contact precautions, droplet precautions, and airborne precautions.  Some illnesses require more than one type of precaution.

When patients are acutely ill with infectious diseases, they are unlikely to seek dental treatment.  It is critical to understand when to use additional precautions if infective patients must be seen, for example in a hospital setting, if an ill patient seeks urgent treatment, or if a healthcare worker becomes infected. 

Transmission-Based Precautions

In addition to standard precautions, contact precautions reduce the risk of transmission of epidemiologically important microorganisms by direct or indirect contact.³  Direct contact involves skin-to-skin contact and physical transfer of microorganisms to a susceptible host from an infected or colonized person.  Indirect-contact transmission involves contact of a susceptible host with a contaminated object (See chart for contact precautions).  Contact precautions apply to patients known or suspected to be infected or colonized with a serious pathogen that might be transmitted by direct or indirect contact. Examples of these illnesses are: gastrointestinal, respiratory, skin or wound infections, or colonization with multi-drug-resistant bacteria judged to be clinically and epidemiologically important.

Examples of infectious conditions requiring contact precautions:

• Clostridium difficile enteric infections
• Ecoli 0157:H7
• Shigella
• Hepatitis A
• Rotavirus
• Respiratory syncytial virus
• Parainfluenza virus
• Enteroviral infections in infants and children
• Highly contagious skin infections (including on dry skin):
  • Diphtheria (cutaneous)
  • Herpes simplex virus (neonatal or mucocutaneous)
  • Impetigo
  • Major abscesses, cellulites, or decubiti
  • Pediculosis (lice)
  • Scabies
  • Staphlococcal furunculosis in infants and children
  • Zoster (disseminated or in immunocompromised)
   
• Viral hemorrhagic infections

Droplet Precautions

Droplet precautions are taken in addition to standard precautions to reduce the risk of droplet transmission of infectious agents contained in large droplets (>5 µm in size) generated from an infected person.⁴ This type of transmission involves contact of the conjunctivae or mucous membranes of the nose or mouth of a susceptible person.  Droplets are generated during coughing, sneezing, or talking, as well as during dental procedures. Droplet transmission requires close contact as the droplets do not usually travel more than 3 feet. Since droplets do not remain suspended in the air, special air handling systems are not required (See chart for droplet precautions). These precautions apply to patients known or suspected to be infected with epidemiologically important pathogens that can be transmitted by infectious droplets.  Examples of droplet-transmitted illnesses are:

• Invasive Haemophilus influenzae type b disease, including meningitis, pneumonia, epiglottitis, sepsis
• Invasive Naisseria meningitides disease, including meningitis, pneumonia, sepsis
• Diphtheria (pharyngeal)
• Mycoplasma pneumonia
• Pertussis
• Pneumonic plague
• Strept. (gp.A) pharyngitis, pneumonia, or scarlet fever in infants and children
• Adenovirus
• Influenza
• Mumps
• Parvovirus B19
• Rubella

Respiratory hygiene/cough etiquette is recommended for dental professionals and patients to control transmission of droplet infections.⁵ The following precautions are recommended for all individuals with signs and symptoms of respiratory infection to contain respiratory secretions.

• Cover the nose/mouth when coughing or sneezing;
• Use tissues to contain respiratory secretions and dispose of them in the nearest waste receptacle after use; and
• Perform hand hygiene after having contact with respiratory secretions and contaminated objects/materials; and wash hands with nonantimicrobial or antiseptic soap and water or use waterless alcohol-based hand rub.

Healthcare facilities should ensure the availability of materials for adhering to respiratory hygiene/cough etiquette in reception areas.

• Provide tissues and to-touch receptacles for used tissue disposal; 
• Provide alcohol-based hand rubs in common areas and reception rooms; and
• Ensure that supplies for handwashing (ie, soap, disposable towels) are consistently available at sinks.

Airborne Precautions  

In addition to standard precautions, airborne precautions prevent transmission of serious illnesses that are disseminated and transmitted by either airborne droplet nuclei (small-particle residue of evaporated droplets, 5 microns or less in size, that remain suspended in air for long periods of time) or dust particles containing infectious agent(s).⁶  Airborne microorganisms carried by small droplet nuclei or dust particles can travel long distances on air currents from the source person.  Special air handling and ventilation systems are required to prevent airborne transmission and fit-tested N-95 respirators are required for susceptible workers to treat infected patients.  Airborne precautions apply to patients known or suspected to be infected with pathogens that are transmitted by the airborne route. Healthcare workers with airborne diseases should be restricted from work. Examples of airborne illnesses include:

• Measles
• Varicella (including disseminated zoster)
• Tuberculosis

Conclusion

Every day, for every patient, consistent and effective standard precautions will prevent most infections related to patient care.  Hand hygiene remains the single most important infection control precaution for preventing disease transmission and will prevent countless infections. Transmission-based precautions are necessary when patients have serious infectious diseases, transmitted by contact, droplets, or small airborne particles. 

*OSAP member and consultant on infection control.

References:

1. Guidelines for Infection Control in Dental Health Care Settings---2003, Centers for Disease Control MMWR Dec. 19, 2003 / 52(RR17);1-61.
2. Standard Precautions, Guideline for Isolation Precautions in Hospitals, Department of Health and Human Services, Centers for Disease Control and Prevention, http://www.cdc.gov/ncidod/dhqp/gl_isolation_Standard.html
3. Contact Precautions, Guideline for Isolation Precautions in Hospitals, Department of Health and Human Services, Centers for Disease Control and Prevention, http://www.cdc.gov/ncidod/dhqp/gl_isolation_contact.html
4. Droplet Precautions, Guideline for Isolation Precautions in Hospitals, Department of Health and Human Services, Centers for Disease Control and Prevention,  http://www.cdc.gov/ncidod/dhqp/gl_isolation_droplet.html
5. Respiratory Hygiene/Cough Etiquette  (www.cdc.gov/flu/professionals/infectioncontrol/resphygiene.html)
6. Airborne Precautions, Guideline for Isolation Precautions in Hospitals, Department of Health and Human Services, Centers for Disease Control and Prevention, http://www.cdc.gov/ncidod/dhqp/gl_isolation_airborne.html
7. Guidelines for Isolation Precautions in Hospitals, Department of Health and Human Services, Centers for Disease Control and Prevention, http://www.cdc.gov/ncidod/dhqp/gl_isolation_table.htm.