Spread of infection within a hospital requires 3 elements: a source of infecting organisms, a susceptible host, and a means of transmission for the organism.

The source of the infecting agent may be patients, personnel, or on occasion, visitors, and may include persons with acute disease, persons in the incubation period of the disease, or persons who are colonized by the infectious agent but have no apparent disease. Another source of infection can be the person's own endogenous flora (autogenous infection). Other potential sources are inanimate objects in the environment that have become contaminated, including equipment and medications.

Patients' resistance to pathogenic microorganisms varies greatly. Some persons may be immune to or able to resist colonization by an infectious agent; others exposed to the same agent may establish a commensal relationship with the infecting organism and become asymptomatic carriers; still others may develop clinical disease. Persons with diabetes mellitus, lymphoma, leukemia, neoplasia, granulocytopenia, or uremia and those treated with certain antimicrobials, corticosteroids, irradiation, or immunosuppressive agents may be particularly prone to infection. Age, chronic debilitating disease, shock, coma, traumatic injury, or surgical procedures also make a person more susceptible.

Microorganisms are transmitted by various routes, and the same microorganism may be transmitted by more than 1 route. For example, varicella-zoster virus can spread either by the airborne route (droplet nuclei) or by direct contact. The differences in infectivity and in the mode of transmission of the various agents form the basis for the differences in isolation precautions that are recommended in this guideline.

There are 4 main routes of transmission—contact, vehicle, airborne, and vectorborne.

This section contains information essential to understanding and properly using the isolation precautions that appear in the guideline and on the instruction cards. Many of the techniques and recommendations for isolation precautions are appropriate not only for patients known or suspected to be infected but also for routine patient care. For example, gowns are appropriate for patient-care personnel when soiling with feces is likely, whether or not the patient is known or suspected to be infected with an enteric pathogen, and caution should be used when handling any used needle.

Handwashing is the single most important means of preventing the spread of infection. Personnel should always wash their hands, even when gloves are used, after taking care of an infected patient or one who is colonized with microorganisms of special clinical or epidemiologic significance, for example, multiply-resistant bacteria. In addition, personnel should wash their hands after touching excretions (feces, urine, or material soiled with them) or secretions (from wounds, skin infections, etc.) before touching any patient again. Hands should also be washed before performing invasive procedures, touching wounds, or touching patients who are particularly susceptible to infection. Hands should be washed between all patient contacts in intensive care units and newborn nurseries. (See Guideline for Hospital Environmental Control: Antiseptics, Handwashing, and Handwashing Facilities.)

When taking care of patients infected (or colonized) with virulent or epidemiologically important microorganisms, personnel should consider using antiseptics for handwashing rather than soap and water, especially in intensive care units.

Category-specific isolation precautions is 1 of 2 isolation systems recommended by CDC. This system was the only one recommended in the first 2 editions of the CDC manual, Isolation Techniques for Use in Hospitals. Isolation categories are derived by grouping diseases for which similar isolation precautions are indicated. For diseases to be grouped into isolation categories, more isolation precautions must be required with some diseases than just those that are necessary to prevent transmission of those diseases. (Hospitals wishing to avoid overuse of isolation precautions may use the alternative isolation system, disease-specific isolation precautions.) Nevertheless, category-specific isolation precautions have advantages in that they are easier to administer and to teach personnel.

Seven isolation categories are used: Strict Isolation, Contact Isolation, Respiratory Isolation, Tuberculosis (AFB) Isolation, Enteric Precautions, Drainage/Secretion Precautions, and Blood/Body Fluid Precautions. The specifications for each category and the diseases and conditions included in the category are discussed below. (Additional information essential to understanding and properly using category-specific isolation precautions is contained in the preceding section, Techniques for Isolation Precautions, and in Table A, Category-Specific Isolation Precautions.)

Strict Isolation is an isolation category designed to prevent transmission of highly contagious or virulent infections that may be spread by both air and contact.

1. Private room is indicated; door should be kept closed. In general, patients infected with the same organism may share a room.

2. Masks are indicated for all persons entering the room.

3. Gowns are indicated for all persons entering the room.