Infection Prevention and Control in the Health Care Setting

Methods of Environmental Cleaning and Disinfection

Liquid chemicals used for environmental cleaning are also low-level disinfectants, and, if applied correctly, can serve both purposes. Environmental cleaning and disinfection focus on surfaces that are repeatedly soiled, such as bathrooms and surfaces that are “high touch.” Even floors should be considered as potential sources of transmission to patients; guidelines recommend use of disinfectant floor cleaners in wards with high endemic rates of multidrug-resistant organisms (MDROs). Cleaning solutions that contain quaternary ammonium compounds are relatively ineffective at killing C. difficile spores and inactivating nonenveloped viruses such as norovirus. Hydrogen peroxide and bleach solutions have activity against these pathogens, in addition to standard viruses and vegetative bacteria, and may be preferable for routine environmental cleaning and disinfection.

C. difficile spores and MDROs, particularly those that are hardy (e.g., resist desiccation, tolerate a range of temperatures) such as VRE, Acinetobacter baumannii, and Candida auris, contaminate the environment in the rooms of patients who are colonized with these bacteria. Several techniques developed to enhance environmental disinfection have been tested in clinical trials, most notably machines emitting hydrogen peroxide and ultraviolet light.

Hydrogen peroxide vapor treatment requires rooms, or entire wards, to be sealed, disconnected from air handling systems, and then filled with vapor at a concentration that is monitored and adjusted throughout the treatment. The treatment, which must be administered by specially trained technicians, inactivates heavy concentrations of vegetative bacteria and spores, even in the presence of proteinaceous material. Its potent inactivation of viruses made it the decontamination method of choice in Europe, the United Kingdom, and the United States during the 2014–15 Ebola virus outbreak (see later). Another form of hydrogen peroxide, an aerosolized mist, is aimed more directly on targets of disinfection and has less impact on microbial contamination in vitro.

Ultraviolet light–emitting devices for environmental disinfection use low-pressure mercury vapor lamps to emit germicidal ultraviolet C (UV-C) wavelengths or use pulsed xenon-generating broad-spectrum ultraviolet light that includes UV-C wavelengths. Prospective clinical trials have evaluated the ability of hydrogen peroxide vapor and UV-C disinfection, as adjuncts to terminal room cleaning, to reduce the risk that newly admitted patients would acquire MDROs from prior room occupants. A single-center, prospective cohort study found that standard terminal room cleaning followed by hydrogen peroxide vapor treatment reduced the risk of MDRO acquisition by more than 60% compared with standard cleaning. A large cluster-randomized crossover trial compared four arms (standard cleaning, standard cleaning followed by UV-C, bleach cleaning, and bleach cleaning followed by UV-C), and found that the addition of UV-C to standard cleaning reduced subsequent acquisition of pathogens by 30%. Oddly, standard cleaning followed by UV-C had a greater impact than bleach cleaning followed by UV-C, and the addition of UV-C to bleach cleaning had no impact on acquisition of C. difficile infection. Clinical outcome data from these trials suggest that these adjunctive modalities do reduce nosocomial transmission of pathogens above and beyond what is accomplished with manual cleaning. Ultraviolet devices can be used by trained housekeeping staff, and may be worthwhile for targeted use if financially feasible.

Transmission of Waterborne Pathogens

Waterborne pathogens can be transmitted to patients via aerosols, such as through a shower or room humidifier, cooling tower, or aspiration while drinking water. Recent outbreaks of deep-seated nontuberculous mycobacterial infections among cardiac surgery patients around the globe were traced to heater-cooler units that aerosolized the bacteria from contaminated water tanks in the direction of the surgical field. Some waterborne bacteria may be transmitted indirectly from hands or objects that had contact with contaminated water, such as bath supplies and linens or by means of tap water used inappropriately for respiratory care of ventilated patents or rinsing of respiratory therapy or endoscopic equipment in tap water. As in most nosocomial infections, the precise route of transmission is often unknown, even when the link to a water source is apparent.

Biofilms in Hospital Plumbing

Biofilms in the pipes and outlets of water distribution systems provide the environment for growth of Legionella, mycobacteria, Pseudomonas , Sphingomonas, and other waterborne organisms. Eliminating bacteria that dwell in biofilms is difficult because they are somewhat impervious to disinfectants. Stagnation of water, due to pipe design or low flow, creates optimal conditions for biofilm formation and colonization. Certain water pipe formations, such as dead legs and long horizontal runs of pipe, contribute to stagnation and are discouraged in hospital construction guidelines. Many older facilities have convoluted plumbing that has, over time, developed low-flow zones and may be more vulnerable to water system colonization with Legionella, mycobacteria, and others. Cooling towers have been implicated in nosocomial and community outbreaks. Biofilms can also form at the points of use; electronic eye faucets, aerators, ice machines, decorative fountains, and other items that are at the interface between water and patients can become colonized and have been implicated in nosocomial transmission.

Legionnaires’ Disease

Legionnaires’ disease, a potentially severe pneumonia caused by Legionella species , is an important health care–associated infection. Legionella pneumophila, the species responsible for the vast majority of infections, is one of the most dreaded nosocomial waterborne pathogens. The mortality rate of hospital-acquired legionnaires’ disease is approximately 32%, more than three times higher than that of community-acquired infection, likely because of the underlying comorbidities of hospitalized patients. Although most legionnaires’ disease is acquired in the community, approximately 33% of outbreaks occur in health care facilities, accounting for 85% of deaths due to legionnaires’ disease outbreaks. As described elsewhere (see Chapter 232 ), the most immunologically vulnerable patients in the hospital and those with advanced age and chronic lung disease are at highest risk for nosocomial legionnaires’ disease.

Legionella experts are divided regarding proper primary prevention of nosocomial Legionella outbreaks and whether hospital water should be cultured prospectively for Legionella spp. The Centers for Disease Control and Prevention (CDC) recommends close clinical surveillance for Legionella infection and a low threshold for investigation when a suspected nosocomial case occurs. Other sources, including published guidelines in much of Europe, recommend routine sampling and testing of hospital water even when no nosocomial infections have occurred. Most would agree with testing water regularly for the presence of Legionella after an outbreak has already occurred, for secondary prevention.

Disinfection of Hospital Water

Water circulating in health care facilities should have adequate concentrations of disinfectant at the point of use. Although most municipal water may be adequately chlorinated, free chlorine, the component of total chlorine that has antimicrobial activity, can dissipate as water travels through the water distribution system, leaving low residual levels at the patient room faucet. If hospital chlorine measurements are performed at a central location, the concentrations that directly affect patient safety will not be apparent. Supplemental disinfection systems add chlorine (in the form of sodium hypochlorite, or bleach), monochloramine, chlorine dioxide, ozone, or copper-silver ions to the water supply. Even when seemingly optimal supplemental disinfection is used, clinicians must be vigilant for breakthrough contamination, which generally manifests earliest as infections among the most immunocompromised or critically ill patients.

Wastewater Plumbing Contamination

A more recently recognized aqueous threat to hospitalized patients is contamination of sink drains and other drains in rooms of patients with MDROs. Although the drains are not in direct contact with patients, experimental studies have demonstrated the dispersal of organisms from the sink drain when water from the faucet splashes back from the drain or its sieve. Resistant organisms may also disseminate in an aerosol when hospital toilets are flushed. In one quasiexperimental study, addition of a lid to ICU hoppers (toilet-like waste disposal fixtures) and biofilm-inhibiting devices to sink drains reduced by half the nosocomial acquisition of carbapenemase-producing organisms.

Air Handling for Airborne Infections

Patients infected with airborne infections, such as tuberculosis, measles, and chickenpox, cough or exhale pathogens in tiny droplets that travel and remain viable in air currents, and can infect susceptible persons who are in the path of airflow from the affected patient. Health care personnel and other patients outside the room of a patient with an airborne infection may be exposed when the door is opened, and such exposures have been documented in health care outbreaks. Therefore, hospitalized patients who have suspected or known airborne infection should be housed in airborne isolation rooms—private rooms that have monitored negative airflow with respect to the anteroom or hallway, and 6 to 12 air changes per hour, with the exhausted air filtered through a high-efficiency particulate air (HEPA) filter or released to the outside. Negative airflow draws infectious particles toward the patient and prevents their dispersal out of the room when the door is opened.

Air Handling to Prevent Nosocomial Mold Infections

Patients who have prolonged neutropenia during treatment of leukemia, stem cell transplantation, and some immunotherapies are highly vulnerable to nosocomial mold infections (see Chapter 306 ). Mold spores, which are as small as 2 to 4 μM, are ubiquitous and easily disseminate in the hospital via air currents, dust, and other particulate matter. Protective isolation rooms are equipped with HEPA-filtered air intake, use positive pressure airflow with at least 12 air changes per hour to repel air currents that carry mold spores, and have seams and cracks sealed to prevent incursion of mold spores through tiny breaches in the envelope of the room. When vulnerable patients leave their rooms and their wards for tests or procedures, they are usually entering areas of the hospital that do not have special environmental precautions, and where they may be exposed to mold spores. Directional airflow and HEPA filtration are also used to minimize escape of fungal spores from construction sites within the hospital. Exposure to construction is a well-described risk factor for invasive mold infections among neutropenic patients, and planned engineering measures, in addition to traffic control and other dust containment measures, can significantly reduce the mold spore content of air near an indoor construction zone. Neutropenic patients who leave their rooms are advised to don surgical masks, which offer little protection against mold spores, or less commonly N95 respirators, which have not been tested for protection against mold infections.

Air Handling in the Operating Room

Operating rooms require fresh, filtered air in order to prevent surgical site infections. Operating rooms should have positive pressure airflow with respect to the surrounding rooms and hallway, with at least 20 filtered air changes per hour, including fresh (outside) air. Airflow can be laminar or directional within the room, such that it enters at the ceiling and exhausts near the floor. Operating room air must be maintained at a moderate range of humidity, 20% to 60%, in order to minimize risk of both static electricity (low humidity) and conditions that promote microbial growth (high humidity).

Air Quality

Routine air samples for fungal culture are not recommended. Air samples may be collected as part of an investigation of a suspected cluster or outbreak of nosocomial mold infections. Even then, they are rarely helpful because there is not a clear correlation between air sample mold growth and risk to patients. In addition, mold outbreaks among immunocompromised patients are typically polyclonal, and air samples often capture different species or strains than those that are relevant in the outbreak. Use of enhanced clinical monitoring and surveillance for possible nosocomial mold infections is recommended in order to detect possible acquisition from the hospital environment. An exception is the required microbiologic air sampling that must be conducted in hospital pharmacies and clean-room laboratories in which medications or cell products are prepared for intravenous infusion. In such facilities, routine air sampling is a required part of an environmental monitoring program to ensure sterility of parenteral solutions.