Transmission of infection within a health-care facility requires three elements - 1) a source of infectious microorganisms, 2) a susceptible host, and 3) a means for microbial transmission. Transmission can occur through several routes, and the same microorganism may be spread by more than one route. The five main routes of transmission include 1) contact, 2) droplet, 3) airborne, 4) common vehicle (e.g., via contaminated items such as food, water or equipment), and 5) vectorborne.
Contact transmission is the most important and frequent mode of nosocomial infection. It is divided into two subgroups: direct contact and indirect contact transmission. Direct contact involves a direct surface-to-body ontact and the physical transfer of microorganisms between a susceptible host and an infected or colonized person. Indirect contact transmission involves contact of a susceptible host with a contaminated intermediate object - usually inanimate - such as contaminated instruments, hands, or gloves.
Droplet transmission is a form of contact transmission. Droplets are generated from a source patient, primarily during coughing, sneezing, or talking, and during the performance of certain procedures. Transmission occurs when microbes are propelled a short distance through the air into the eyes, nasal mucosa, or mouth of a susceptible host.
Airborne transmission occurs by dissemination of either airborne-droplet nuclei (small particle residue usually five microns or smaller) of evaporated droplets containing microbes that remain suspended in the air for long periods of time, or by dust particles containing the infectious agent. Microorganisms carried in this manner can be dispersed widely by air currents, and they can be inhaled by a susceptible host, often located at a distance from the source patient.
A special effort has been made by The Centers for Disease Control and Prevention to develop effective infection-control measures for decreasing transmission of microorganisms.
To prevent the transmission of all respiratory infections, including influenza, a number of procedures need to be implemented at the first point of contact with infected persons. Respiratory hygiene and cough etiquette can be incorporated into infection-control practices as one component of standard precautions. The process involves four elements - 1) visual alerts, 2) respiratory hygiene and cough etiquette, 3) separation of persons with respiratory symptoms, and 4) droplet precautions.
Visual alerts (in appropriate languages) need to be posted to instruct patients and persons who accompany them to inform practice personnel of the symptoms of a respiratory infection when they arrive. They are then asked to practice proper preventive procedures.
Measures to contain respiratory secretions are recommended for all individuals with signs and symptoms of a respiratory infection. They include:
• Covering the nose or mouth when sneezing or coughing.
• Using tissues to contain respiratory secretion and disposing them in the nearest waste receptacle after use.
• Performing hand hygiene (e.g., handwashing with non-antimicrobial soap and water, alcohol-based hand rub or antiseptic hand wash) after having contact with respiratory secretions and contaminated objects or materials.
Health-care facilities should assure the availability of materials for adhering to respiratory hygiene and cough etiquette in waiting and treatment rooms. These include:
• Providing tissues and no-touch receptacles for used tissue disposal.
• Providing conveniently located dispensers of alcohol-based hand rub. Where sinks are available, ensure that supplies for handwashing (e.g., soap and disposable towels) are consistently available.
Handwashing frequently is called the single most important measure to reduce the risks of transmitting organisms from one person to another or from one site to another on the same patients. Proper handwashing protects both patients and practitioners.
During periods of increased respiratory infection activity, masks can be offered to persons who are coughing. Postponing treatment also is an option. When space is available, encourage coughing or sneezing persons to sit at least three feet away from others. Some facilities have found it easier to institute such recommendations year-round.
Facility personnel should follow droplet precautions (e.g., wearing a mask) in addition to standard precautions when examining or treating a patient with symptoms of a respiratory infection, especially if a fever is present. Maintain droplet precautions as long as symptomatic patients are present or suspected.
Dr. Charles John Palenik is an assistant director of Infection Control Research and Services at the Indiana University School of Dentistry. Dr. Palenik has authored numerous articles, book chapters, and monographs, and is the co-author of the popular "Infection Control and Management of Hazardous Materials for the Dental Team." He serves on the Executive Board of OSAP, dentistry's resource for infection control and safety. Questions about this article or any infection-control issue may be directed to firstname.lastname@example.org.