Sources of Infectious Agents

Humans (patients, personnel, or visitors) are the primary source for infectious agents in the health care setting, but inanimate objects (e.g., contaminated medical equipment, linen, medications) have also been implicated in transmission. A person may have an acute infection with symptoms, may be in the asymptomatic or incubation period of the disease, or may be colonized by pathogens without symptoms. People may also serve as their own source of infection, via endogenous flora. This latter process is called autogenous infection.

Susceptible Hosts

Susceptibility and resistance to infection vary greatly. Some individuals may be immune to infection or able to resist colonization. Others exposed to the same organism may carry it but show no symptoms. Other individuals may develop clinical disease. Host factors, such as poorly controlled diabetes mellitus, extremes of age, and underlying acquired (HIV infection) or iatrogenic (through chemotherapy or anti–tumor necrosis factor inhibitors) immunodeficiency, can enhance susceptibility to infection. Surgical incisions and radiation therapy impair defenses of the skin and organ space. Medical devices, such as urinary tract catheters, central venous catheters, and endotracheal tubes, allow pathogens to increase the risk of infection by impeding local host defenses and providing biofilms that may facilitate adherence of pathogens.

Hospital-acquired or nosocomial infections are infections that are acquired in the hospital. The high incidence of nosocomial gram-negative bacterial pneumonia is associated with factors that promote colonization of the pharynx with these organisms. Gram-negative colonization dramatically increases in critically ill patients, which increases the likelihood of the development of these pneumonias.⁴ Most nosocomial pneumonias occur in surgical patients, especially patients who have had chest or abdominal procedures. In these patients, normal swallowing and clearance mechanisms are impaired, allowing bacteria to enter and remain in the lower respiratory tract. Intubations, anesthesia, surgical pain, and use of narcotics and sedatives impair host defenses further. The risk of pneumonia is not the same for all surgical patients. Patients at the highest risk include elderly patients, severely obese patients, patients with chronic obstructive pulmonary disease (COPD) or a history of smoking, and patients with an artificial airway in place for long periods.⁵

Patients with an artificial tracheal airway are at high risk for nosocomial pneumonia for several reasons. Typically, patients requiring prolonged intubation already have one or more factors predisposing to infection, such as severe COPD. Another risk factor may be increased upper airway colonization with gram-negative bacteria. Because the tube bypasses the normal protective mechanisms of the upper airway, bacteria have easy access to the lower respiratory tract. Finally, handling of these tubes increases the likelihood of cross contamination, particularly during suctioning.

Some pneumonias occur primarily in immunocompromised hosts. Physicians may purposefully suppress a patient’s immune response with drugs, as in organ transplant cases. Alternatively, immunosuppression may be a result of underlying disease, as with AIDS. Immunocompromised hosts, regardless of cause, are highly susceptible to infections, especially infections caused by opportunistic bacteria, fungi, or viruses.

Modes of Transmission

The three major routes for transmission of human sources of pathogens in the health care environment are contact (direct and indirect), respiratory droplets, and airborne droplet nuclei (respirable particles <5 µm). Table 4-1 provides examples of the common transmission routes for selected microorganisms.⁶

Decreasing Host Susceptibility

Decreasing inherent host susceptibility to infection is the most difficult and least feasible approach to infection control. Hospital efforts at this level focus mainly on employee immunization and chemoprophylaxis. Certain immunizations are recommended for susceptible health care personnel to decrease the risk of infection and the potential for transmission to patients and coworkers within the health care facility. The Occupational Safety and Health Administration (OSHA) mandates that employers offer hepatitis B vaccination. Vaccinations of health care workers in the absence of evidence of immunity against varicella, rubella, and measles should be encouraged.⁸ In addition, health care personnel in facilities that care for young infants and children should receive the adult acellular pertussis vaccine. Health care personnel without medical contraindications should also receive an annual influenza vaccination.⁹

Antimicrobial agents and topical antiseptics may be used to prevent outbreaks of selected pathogens. Postexposure chemoprophylaxis is recommended under defined circumstances for Bordetella pertussis (whooping cough), N. meningitidis (meningococcal meningitis), Bacillus anthracis (anthrax), influenza virus, HIV, and group A streptococci.⁶

A large percentage of HAIs are due to device-related infections, including ventilator-associated pneumonia (VAP), catheter-related bloodstream infection, and catheter-associated urinary tract infection. The best way to decrease host susceptibility to a device-related infection is first to limit device use and second to ensure that devices are placed and maintained appropriately. Prevention bundles—defined as the use of multiple different evidence-based best practices to prevent device-related infection—have been shown to decrease the incidence of HAIs significantly.10,11 Boxes 4-1 and 4-2 list the components of the central line bundle for vascular catheter placement and the VAP bundle. Institutions should be committed to these processes of care, and individual health care workers should be familiar with these practices and execute them on a routine basis.^12,13

Eliminating the Source of Pathogens

It is impossible to eliminate all pathogens from any working environment. Nonetheless, standard infection control procedures always include efforts to eliminate pathogens, and recommended practices for cleaning and disinfecting noncritical surfaces in patient care areas should be followed. Infection control procedures designed to remove environmental pathogens fall into two major categories: general sanitation measures and specialized equipment processing.

If the environment is dirty, all other infection control efforts are futile. General sanitation measures help to keep the overall environment clean. General sanitation aims to reduce the number of pathogens to a safe level. This reduction is achieved through sanitary laundry management, food preparation, and housekeeping. Environmental control of the air (using specialized ventilation systems) and water complements these efforts.

The goal of specialized equipment processing is to decontaminate equipment capable of spreading infection. Equipment processing involves cleaning, disinfection, and sterilization (when necessary). Methods that kill bacteria are bactericidal, whereas methods and techniques that inhibit the growth of bacteria are bacteriostatic. Methods that destroy spores are sporicidal, and methods that destroy viruses are virucidal.

Interrupting Transmission

General sanitation measures and equipment processing have limits. To prevent the spread of infections between patients and to keep themselves healthy, health care personnel also must take measures to stop infection. There are two tiers of HICPAC and Centers for Disease Control and Prevention (CDC) transmission precautions: standard precautions and transmission-based precautions.⁶

Standard Precautions

Standard precautions are intended to be applied to the care of all patients in all health care settings all the time. This is the primary strategy for the prevention of health care–associated transmission of infections among patients and health care personnel. From a health care worker protection perspective, application of standard precautions on a routine basis is recognition that all blood, body fluids, secretions, and excretions with the exception of sweat and urine may contain transmissible infectious agents. To mitigate against this risk, a health care worker should employ personal protective equipment (PPE). PPE refers to various barriers and respirators used alone or in combination to protect mucous membranes, skin, and clothing from contact with infectious agents. Gloves, gowns, masks, eye protection, and face shields should be employed depending on the anticipated exposure.

The application of standard precautions by health care personnel during patient care depends on the nature of the interaction and the extent of anticipated blood, body fluid, or pathogen contact. For some patient care situations, only gloves are required. In other cases, gloves, gowns, and face shield may be required. Box 4-3 describes standard precautions, including hand hygiene; use of gloves, masks, and eye protection; equipment handling; and patient placement.

Hand Hygiene

The importance of hand hygiene to reduce the transmission of infectious agents cannot be overemphasized and is an essential element of standard precautions.¹⁴ Hand hygiene includes handwashing with either plain or antiseptic-containing soap and water for at least 15 seconds and the use of alcohol-based products (gels, rinses, and foams) containing an emollient that does not require the use of water. In the absence of visible soiling of hands, approved alcohol-based products are preferred over antimicrobial or plain soap and water because of their superior microbicidal activity, reduced drying of skin, and convenience. The quality of performing hand hygiene can be affected by the type and length of fingernails and by wearing jewelry. Artificial fingernails and extenders are discouraged because of their association with infections.¹⁴ Figure 4-2 illustrates the proper technique for handwashing.

Gloves

Gloves protect both patients and health care workers from exposure to pathogens that may be carried on the hands of health care workers. Gloves protect caregivers from contamination when contacting blood, body fluids, secretions, excretions, mucous membranes, and nonintact skin of patients and when handling or touching visibly or potentially contaminated patient care equipment and environmental surfaces.¹⁴

Caregivers should wear sterile gloves whenever performing invasive procedures. A single pair of nonsterile disposable gloves (e.g., latex, vinyl, nitrile) may be used for routine patient care. Gloves should be changed, regardless of use, between each patient contact and after any direct contact with infectious material, even if in the middle of a procedure. After removing the gloves, caregivers must always wash their hands. Gloves may have small, invisible defects or may be torn during use. The hands can be contaminated during removal of the gloves. For these reasons, the wearing of gloves should never be used as a substitute for handwashing.

Mouth, Nose, Eye, and Face Protection

Face protection is an important component of standard precautions because the mucous membranes of the eyes, nose, and mouth are particularly vulnerable to some types of pathogens. Masks protect mucosal surfaces against splashes or sprays but should not be confused with particulate respirators that are recommended for protection from small particles (as described subsequently for airborne isolation [AI]). The wearing of masks, eye protection, and face shields in specified circumstances when exposures are likely to occur (e.g., bronchoscopy suite) is mandated by the OSHA Blood-borne Pathogen Standard.

Respiratory Protection

Respiratory protection (use of NIOSH-approved N-95 or higher level respirator) is intended for diseases (e.g., M. tuberculosis, SARS, smallpox) that could be transmitted through the airborne route.⁶ The term respiratory protection has a regulatory context that includes components of a program required by OSHA to protect workers: (1) medical clearance to wear a respirator, (2) provision and use of appropriate NIOSH-approved fit-tested respirators, and (3) education in respirator use. Information on types of respirators can be found at www.cdc.gov/niosh/npptl/respirators/respsars.html.

Gowns, Aprons, and Protective Apparel

Isolation gowns and other apparel (aprons, leg coverings, boots, or shoe covers) also provide barrier protection and can prevent the contamination of clothing and exposed body areas from blood and body fluid contact and transmissible pathogens (e.g., respiratory syncytial virus and Clostridium difficile). Selection of protective apparel is dictated by the nature of the interaction of the health care worker with the patient, including anticipated degree of body contact with infectious material.⁶ In most instances, gowns are worn only if contact with blood and body fluid is likely. Clinical coats and jackets worn over clothing are not considered protective apparel. Isolation gowns should always be donned with gloves and other protective equipment as indicated. As with gloves and masks, a gown should be worn only once and then discarded. In most situations, aseptically clean, freshly laundered, or disposable gowns are satisfactory.

The emergence of SARS and the ongoing concerns for pandemic infection have led to a strategy of preventing transmission of respiratory infections at the first point of contact within a health care setting (e.g., physician’s office) termed respiratory hygiene/cough etiquette that is intended to be incorporated into infection control practices as one component of standard precautions.⁶ The elements of respiratory hygiene/cough etiquette include (1) education of health care personnel, patients, and visitors; (2) posted signs in language appropriate to the population served with instructions for patients and accompanying family members or friends; (3) source control measures (covering the mouth and nose with a tissue when coughing or placing a surgical mask on a coughing person when possible); (4) hand hygiene after contact with respiratory secretions; and (5) spatial separation (≥3 feet from persons with respiratory infections in common waiting areas).

Transmission-Based Precautions

Transmission-based precautions are for patients who are known or suspected to be infected with pathogens that require additional control measures to prevent transmission. There are three categories of transmission-based precautions: contact precautions, droplet precautions, and airborne infection isolation. Whether used singularly or in combination, these precautions are always used in addition to standard precautions.⁶

Contact precautions are intended to reduce the risk of transmission by direct or indirect contact with the patient or the patient’s environment. Contact precautions intend for spatial separation of infected or colonized patients (≥3 feet between beds), and health care personnel and visitors wear gowns and gloves for all interactions that may involve contact with the patient or the patient’s environment. Contact precautions are most commonly employed to decrease the spread of multidrug-resistant organisms such as C. difficile. Contact precautions are described in Box 4-4.

Droplet precautions are used to prevent a form of contact transmission that occurs when droplets are propelled short distances (≤3 feet through the air). Droplets are often generated with coughing, sneezing, suctioning, bronchoscopy, and cough induction. Health care personnel and visitors should don a mask during all interactions that may involve contact with such patients. Droplet precautions are employed for patients with presumed or confirmed infection with organisms known to be transmitted by respiratory droplets such as influenza. Droplet precautions are described in Box 4-5. Precautions for use when performing cough-inducing and aerosol-producing procedures are described in Box 4-6.

Airborne Infection Isolation

AI refers to isolation techniques intended to reduce the risk of selected infectious agents transmitted by “small droplets” of aerosol particles (e.g., M. tuberculosis).⁶ Persons who enter an AI room must wear respiratory protection (an NIOSH-approved N-95 or higher respirator). Patients should be placed in a single-patient AI room that is equipped with special air handling and ventilation capacity that meets the American Institute of Architects/Facility Guidelines Institute standards (monitored negative pressure relative to surrounding area, two air exchanges per hour, and air exhausted directly to the outside or recirculated through high-efficiency particulate air/aerosol [HEPA] filtration). In settings where AI cannot be implemented because of limited resources, one should implement physical separation, mask patients, and provide respiratory protection for health care personnel to reduce the likelihood of airborne transmission. Box 4-7 describes airborne precautions that should be used in addition to standard precautions.

Protective Environment

A specialized engineering approach to protect highly immunocompromised patients is a protective environment. A protective environment is used for patients with allogeneic hematologic stem cell transplants to minimize fungal spore counts in the air.¹⁵ The rationale for such controls has been studies showing outbreaks of aspergillosis associated with construction. Air quality for patients with hematologic stem cell transplants is improved through a combination of environmental controls that include (1) HEPA filtration of incoming air, (2) directed room airflow, (3) positive room air pressure relative to the corridor, (4) well-sealed rooms to prevent infiltration of outside air, (5) ventilation to provide 12 or more air changes per hour, (6) strategies to reduce dust, and (7) prohibition of dried and fresh flowers and potted plants in rooms.

Patient Placement

It is increasingly thought that single-occupancy rooms increase patient safety; reduce infection, injuries, falls, and medical errors; and reduce sources of environmental stress (e.g., noise). However, most facilities are not single occupancy only, and patient placement in private rooms is prioritized for patients who have conditions that may result in the transmission of infections to other patients or who are at increased risk for acquisition of HAIs.

Single-patient rooms are always indicated for patients on AI and in a protective environment. Single-patient rooms are preferred for patients who require contact precautions (e.g., C. difficile) or droplet precautions (e.g., influenza).

Cohorting is a practice of grouping patients with the same infection (or colonized with the same organism) together to confine care geographically and prevent transmission to other patients. Cohorting based on the presenting clinical syndrome is commonly used in pediatric hospitals during respiratory syncytial virus/influenza season. Cohorting health care workers to care only for patients infected or colonized with a particular transmissible pathogen may also limit transmission to uninfected patients.

Transport of Infected Patients

By limiting the transport of patients with contagious disease, the risk of cross infection can be reduced. However, infected patients sometimes do need to be transported, and when that occurs, the patient needs to wear appropriate barrier protection (mask, gown, impervious dressings) consistent with the route and risk for transmission.⁶ Health care personnel receiving the patient need to be notified of the patient’s impending arrival and what infection control measures are required.

Spaulding Approach to Disinfection and Sterilization of Patient Care Equipment

In 1968, Spaulding published his approach to disinfection and sterilization, which was based on the degree of risk of infection involved in the use of the item in patient care.¹⁷ The three categories he described were critical, semicritical, and noncritical (Table 4-3). Critical items are categorized based on the high risk of infection if such an item is contaminated with pathogens, including bacterial spores (e.g., items that enter sterile tissue or the vascular system). Critical devices enter normally sterile tissues. Most of these items should be purchased sterile or be sterilized, by steam sterilization if possible. Semicritical items come into contact with mucous membranes or nonintact skin; this includes most respiratory equipment. These items should be free of all microorganisms before use (bacterial spores may be present). Semicritical items require at least high-level disinfection using chemical disinfectants. Noncritical items come into contact with intact skin (an effective barrier to most microbes) but not mucous membranes. Most noncritical reusable devices may be decontaminated where they are used (e.g., bedpans, patient bed rails).

Cleaning

Medical equipment must be cleaned and maintained according to the manufacturer’s instructions. Noncritical items, such as commodes, intravenous pumps, and ventilator surfaces, must be thoroughly cleaned and disinfected before use with another patient. Cleaning is the first step in all equipment processing. Cleaning involves removing dirt and organic material from equipment, usually by washing (see Table 4-3).¹⁶ Failure to clean equipment properly can render all subsequent processing efforts ineffective. Cleaning should occur in a designated facility with separate dirty and clean areas. Before being cleaned, the equipment should be disassembled and examined for worn parts. Complete disassembly helps ensure good exposure to the cleaning agent. After disassembly, the parts should be placed in a clean basin filled with hot water and soap, detergent, or enzymatic cleaners.

Because water alone cannot dissolve organic matter, soaps or detergents should be used to clean equipment. Soaps act by reducing surface tension and forming an emulsion with organic matter. Soaps have little bactericidal activity and work poorly in hard water. A detergent refers to a substance (usually a chemical agent but sometimes a physical one) applied to inanimate objects that destroys disease-causing pathogens but not spores. Detergents work in hard water but can be inactivated by proteins. Most detergents are weakly bactericidal but against gram-positive bacteria only. Some commercial products combine a germicide with a detergent, providing the dual action of cleaning and disinfection. Although careful cleaning removes most pathogens from the equipment, it cannot eliminate the risk of infection. For this reason, most equipment must undergo either disinfection or sterilization.

Disinfection

Disinfection describes a process that destroys the vegetative form of all pathogenic organisms on an inanimate object except bacterial spores. By definition, disinfection differs from sterilization by its lack of sporicidal activity.¹⁶ However, a few disinfectants kill spores with prolonged exposure times (hours) and are called chemical sterilants. Disinfection can involve either physical or chemical methods. The most common physical method of disinfection is pasteurization. Many chemical methods are used to disinfect respiratory care equipment.

Sterilization

Sterilization destroys all microorganisms on the surface of an article or in a fluid, which prevents transmission of pathogens associated with the use of that item. Both physical and chemical means can achieve sterilization. Physical methods include various forms of heat (steam) and ionizing radiation. Chemical methods of sterilization include low-temperature sterilization technologies such as ethylene oxide (EtO) gas. Table 4-5, excerpted from the CDC guideline for sterilization and disinfection, compares and contrasts the major methods of sterilization.¹⁶

Medical devices that have contact with sterile body tissues or fluids are crucial items and should be sterile before use. If the object is heat resistant, steam sterilization is usually recommended. However, increases in the use of medical devices that are heat and moisture sensitive have necessitated the development of low-temperature sterilization technology. These include, but are not limited to, EtO, hydrogen peroxide gas plasma, and peracetic acid. A review of the commonly used sterilization technologies with a summary of advantages and disadvantages can be found in the updated CDC guidelines for disinfection and sterilization in health care facilities.¹⁶ Following is an overview of a few of these technologies.

Maintenance of In-Use Equipment

In-use respiratory care equipment that can spread pathogens includes nebulizers, ventilator circuits, bag-valve-mask devices (manual resuscitators), and suction equipment. Oxygen therapy and pulmonary function equipment are also implicated as potential sources of nosocomial infections.

Processing Reusable Equipment

Improperly processed reusable equipment is another potential source for pathogens. General principles for cleaning, disinfection, and sterilization were provided previously. This section presents specific guidelines for processing reusable respiratory care equipment and a special section on bronchoscope disinfection.

Disposable Equipment

An important alternative to reprocessing equipment continually is the use of single-patient-use disposable devices. In the past, only oxygen therapy devices (i.e., masks, cannulas), suction apparatus (i.e., catheters, tubing), and some supplies were disposable. Today, manufacturers provide a whole range of disposable devices, including humidifiers, nebulizers, incentive spirometers, ventilator circuits, bag-valve-masks, and monitoring transducers.

Three major issues are involved in using disposable devices: cost, quality, and reuse. Cost issues boil down to straightforward dollar comparisons between purchasing and processing reusable devices versus stocking and distributing disposable devices. Good comparisons take into account direct and indirect costs (e.g., personnel, inventory, maintenance) and risk factors. Most recent findings support the cost-effectiveness of disposable devices over reusable devices in respiratory care.

Cost savings notwithstanding, many quality issues persist. Although disposable devices generally perform well, poor quality control remains a problem.²³ Respiratory care managers need to evaluate carefully disposable devices being considered for bulk purchase before actual clinical use.²⁴ To ensure reliability, this evaluation should include physical testing of multiple units of each model being assessed. Finally, bedside clinicians need to inspect carefully and confirm the operation of any disposable device before use.

Reusing high-cost, high-volume disposable equipment saves hospitals money. The practice of reusing devices labeled by the manufacturer for “single-use only” raises significant safety concerns and issues of negligence.²⁵ The CDC recommends that single-use devices be considered for reuse only if there is good evidence that reprocessing poses no threat to the patient and does not alter the function of the device.⁴ Individuals responsible for reusing disposable equipment bear a significant burden of proof. Without such proof, users of reprocessed single-use devices may be transferring legal liability for the safe performance of the product from the manufacturer to themselves or their employer.²⁶

Fluids and Medications Precautions

Unit dosing has decreased but has not eliminated the infection hazard associated with medications. Box 4-13 outlines several simple procedures designed to help prevent cross contamination while using fluids and medications.

Handling Contaminated Articles and Equipment

Contaminated items, whether reusable or disposable, should be enclosed in an impervious bag before removal from a patient’s room. Bagging helps prevent accidental exposure of both personnel and the environment to contaminated articles. A single bag is satisfactory if (1) the bag is strong and impervious, and (2) the contaminated items can be bagged without contaminating the outer surface of the bag. Otherwise, the contaminated items should be double-bagged. Bags used for contaminated articles or waste materials should be clearly labeled or color-coded for this purpose.

After bagging, reusable patient care equipment must be returned to the applicable processing area. Contaminated reusable equipment should remain bagged until ready for decontamination or sterilization. When contaminated waste is being discarded, both OSHA procedures and any applicable local, state, or federal regulations must be followed.

Using Needles and Syringes

Needlestick injuries are a growing area of concern among health care personnel because accidental skin puncture with a contaminated sharp can transmit blood-borne pathogens such as hepatitis C and HIV to the health care worker.² All health care workers should exercise extreme caution when handling any sharp instruments, including needles and syringes.

Handling Laboratory Specimens

When gathering laboratory specimens (e.g., sputum), extreme care needs to be taken to prevent contamination of the external surface of the container. If the outside of the container is contaminated, the caregiver must either disinfect it or place it in an impervious bag. To minimize the likelihood of laboratory specimens leaking during transport, they should always be placed in a sturdy container with a secure lid. When gathering a specimen from a patient on isolation precautions, the container must be placed in an appropriately labeled, impervious bag before it is removed from the room.