Chapter 4. Infection Control and Surveillance in the Intensive Care Unit

• Focused surveillance for nosocomial infections is the cornerstone of infection control activities in the ICU.
• Commonly used invasive devices such as central venous and urinary catheters and endotracheal tubes are significant risk factors for nosocomial infection. Evidence-based ICU policies and procedures and staff education can reduce the risk of device-related infections.
• Antibiotic resistance is an increasing problem, and its containment and prevention require a multifactorial approach, including adequate hand hygiene, surveillance for resistant pathogens, enforced infection control precautions, and prudent use of antibiotics.
• Standard infection control precautions should be applied to all ICU patients. Precautions for contagious or epidemiologically significant pathogens are based on modes of transmission.

Nosocomial, or hospital-acquired, infections result in significant morbidity and mortality. Nosocomial infections have been reported to affect approximately 2 million hospitalized patients in the United States annually, at an estimated cost of $57.6 billion in 2000.1,2 ICU beds, while only accounting for 5% to 10% of all hospital beds, are responsible for 10% to 25% of health care costs generated.3 Patients admitted to the ICU have been shown to be at particular risk for nosocomial infections, with a prevalence rate as high as 30%.4 Given the increasing strain on health care resources in the United States and other countries and the personal impact that these infections have on patients, the prevention of nosocomial infections in the ICU should be an important goal of any critical care clinician.

A likely explanation to account for the observation that ICU patients are more vulnerable to acquiring a nosocomial infection compared with other hospitalized patients is that critically ill patients frequently require invasive medical devices, such as urinary catheters, central venous and arterial catheters, and endotracheal tubes. Data on a sample of ICUs from the Centers for Disease Control and Prevention (CDC) show that adult ICU patients have central venous catheters in place and receive mechanical ventilation an average of 53% and 42% of their total time spent in the ICU, respectively.5 These devices result in infection by compromising the normal skin and mucosal barriers and serving as a nidus for the development of biofilms, which provide a protected environment for bacteria and fungi. In a survey of cases of ICU-acquired primary bacteremia, 47% were catheter-related.6 While the increased severity of illness of ICU patients makes intuitive sense as a potential risk factor for nosocomial infection, few studies have shown a consistent relationship.7 This may be explained, however, by the fact that scoring systems were developed primarily to predict mortality and may not adequately capture markers for nosocomial infection, such as the need for prolonged parenteral nutrition.

Infection control in the ICU arose from hospital-wide infection control programs developed in response to the staphylococcal pandemic of the late 1950s and early 1960s. In 1976, the CDC initiated the Study on the Efficacy of Nosocomial Infection Control (SENIC) to better understand the impact of infection control programs on nosocomial infection rates in a random sample of 338 U.S. hospitals.8 Programs that had the greatest impact in reducing nosocomial infection rates had the following components: organized surveillance and active intervention in patient care by infection control staff to reduce the risk of infection, a physician trained in infection control methods, a fixed ratio of infection control specialists to patient beds, and a system for reporting surgical infection rate to surgeons. In hospitals that implemented infection control programs meeting these criteria, the incidence of nosocomial infections decreased hospital-wide by 32%, whereas in hospitals with ineffectual programs, infections increased by 18% over a 5-year period. These findings led to regulations requiring that hospitals demonstrate that their infection control programs meet the preceding criteria in order to maintain accreditation.

Surveillance for nosocomial infection is the cornerstone of effective infection control activity in the ICU. Surveillance activity serves several key functions, including the early detection of potential nosocomial outbreaks, the identification of high endemic rates of infection as targets for intervention, and evaluation of the effectiveness of efforts to prevent infection. The process of surveillance itself involves the continuous and systematic collection, tabulation, analysis, and dissemination of information on the occurrence of nosocomial infections within the ICU. It was noted early in the development of infection control programs that feedback of nosocomial infection rates to clinicians, along with active intervention, is a necessary element to a successful program and that collection of surveillance information without this feedback is ineffectual at reducing infection rates.8 Nosocomial infection surveillance in the ICU involves the cooperation of both infection control and ICU personnel for both exchange of data and developing effective infection control measures.

Infection control surveillance, particularly when it involves chart review, can be labor-intensive. Because of the reality that limited resources are available for infection control surveillance and intervention, a practice known as focused or targeted surveillance is commonly employed. This involves both hospital infection control and ICU personnel making determinations of the particular nosocomial infections to be monitored routinely. The factors involved in making the decision include the degree of morbidity or mortality that results from the infection, the frequency that the infection is known or perceived to occur in the ICU, the proportion of ICU patients at risk of becoming infected, the extent to which effective interventions can be implemented by the ICU team, and finally, the perception by both infection control and ICU personnel that a particular infection represents a significant problem for that unit.

Infection control surveillance data in the ICU typically are reported as the occurrence of a particular infection over a defined time period at risk (e.g., cases of ventilator-associated pneumonia per total number of patient days spent on mechanical ventilation per month), also known as an incidence density. For infections that result from a point exposure (e.g., the number of tracheostomy site infections per total number of tracheotomies performed in one quarter), a cumulative incidence can be determined. Cumulative incidence is reported less commonly in the ICU owing to the observation that infections in the ICU result primarily from invasive devices that are in place for days to weeks.

In order for the information collected for infection surveillance to be interpretable, a case definition for infection has to be developed. Criteria for the diagnosis of nosocomial infections have been developed by the CDC9 and are widely accepted. It is important to note that greater accuracy is required on the part of the infection control practitioner in determining if an episode represents a true nosocomial infection compared with the critical care physician, who may initiate antibiotic therapy in the case of a presumptive diagnosis.

Several methods exist for performing surveillance in the ICU, including the traditional methods of medical chart review and review of microbiology, radiology, and autopsy reports. More recently, the use of computerized expert systems and medical informatics in nosocomial infection surveillance has reduced the need for manual chart review, improved case ascertainment, and allowed for more resources to be used for intervention and prevention.10

ICU Design and Layout

While published architectural guidelines require that isolation rooms be included in the layout of critical care units, few data are available to address the impact of ICU design on prevention of nosocomial infection. Mulin and colleagues11 demonstrated a lower rate of bronchopulmonary colonization with Acinetobacter baumannii among mechanically ventilated patients in a surgical ICU after the unit was converted from one with a mixture of enclosed isolation rooms and open rooms to all enclosed rooms with hand washing facilities. Another study demonstrated a reduction in the incidence of ventilator-associated pneumonia and urinary tract infections in a pediatric ICU after it was converted from an open ward to separate isolation rooms, without a significant change in patient to staff ratios.12 Despite the lack of data, it would seem prudent to ensure that adequate access to hand hygiene exists for ICU personnel.

Nursing Staffing Ratios

Much attention has been given recently to the issue of nurse staffing levels and the impact that this has on patient outcomes and complications, including infection. With increased workloads for registered nurses and the reliance on less trained health care personnel for the delivery of care, there is concern that lapses in infection control will occur, resulting in nosocomial infections. In a pediatric cardiac ICU over a 1-year period, a decrease in nurse-to-patient staffing ratios correlated significantly with an increase in nosocomial infections.13 In a multicenter, retrospective cohort study among 2606 patients admitted to an ICU after abdominal aortic surgery, patients cared for in ICUs that reported nurse-to-patient ratio of 1:3 or greater on either day or night shifts were at greater risk of respiratory complications, including postoperative pneumonia.14 This relationship was independent of patient age, comorbidity, level of surgical urgency, ICU size, and hospital procedure volume.

These studies, along with several others, have limitations, including retrospective design, no determination of nursing experience or level of training, and no comment on the role that other types of health care worker staffing levels, such as respiratory therapists, have on nosocomial infections rates. Despite these limitations, a direct association between increased nursing workload and the occurrence of nosocomial infections among ICU patients appears to exist. The optimal level of both nursing staffing and experience needed to minimize the risk of infection in ICUs remains to be determined but is unlikely to be uniform for every type of unit.

Infection Control Policies and Procedures

Given the complexity of delivering care to critically ill patients, policies and procedure are a necessary part of the organization of any ICU. These policies ensure that personnel perform certain procedures, such as central venous catheter insertion and care, in a consistent manner. Written ICU policies should incorporate evidence-based infection control practices. For policies to be effective, they should be clear, concise, and shared with the staff. Policies that are complex or unrealistic either will be ignored or will result in even wider variation in how care is delivered owing to individual interpretation. Most private and state hospital accreditation programs base their review of ICUs not only on whether ICUs have required policies but also on whether they actually follow them. Therefore, it is important that ICU physician and nursing staff review these policies on a routine basis in consultation with infection control practitioners or the hospital infection control committee and revise these policies when needed.

Central Venous Catheters/Pulmonary Arterial Catheters

Catheter-associated bloodstream infection is one of the most common nosocomial infections seen in ICU patients. Approximately 80,000 of these infections have been estimated to occur annually in ICUs in the United States (excluding insertion-site infection and septic thrombophlebitis).15 These infections are associated with increased ICU length of stay, health care costs, and use of broad-spectrum antibiotics.

Risk factors for catheter-associated bloodstream infections include the anatomic catheter insertion site, type of catheter used, and the patient population. The pathogenesis includes microbial colonization of the subcutaneous catheter tract by skin flora with subsequent colonization of the catheter and biofilm formation, as well as colonization of the catheter hub from microbes introduced during use of the catheter. While intravascular catheters can result in bloodstream infections by other means, such as the infusion of contaminated fluids, the mechanisms just mentioned are the primarily methods by which nontunneled central venous catheters in place for less than 2 to 4 weeks cause bloodstream infections.

Numerous infection control practices have been effective in preventing intravascular catheter-related infections (Table 4-1). Meticulous hand hygiene before and after handling intravascular catheters, along with maintaining an intact, nonsoiled dressing at the catheter insertion site, are essential to preventing device-related infections. Maximal sterile barrier precautions (i.e., sterile gowns, gloves, surgical mask and hat, and a large surgical drape) during insertion reduce the incidence of infection.16 In one randomized trial, subclavian vein insertion was associated with a lower incidence of infectious complications and complete vessel thrombosis when compared with femoral insertion.17 Structured educational programs incorporating the use of maximal sterile precautions have reduced the incidence of catheter-associated bloodstream infections by 27% to 66%.18,19 Antibiotic-coated catheters are also effective.20 The unexplored issue of emerging resistance associated with the use of these catheters makes their role in an overall infection control strategy unclear.

Arterial Catheters and Pressure Transducers

Compared with central venous catheters, the incidence of catheter-associated bloodstream infection attributable to arterial catheters has not been as well studied but is estimated to be roughly 1.5% per device or 2.9 cases per 1000 catheter-days.21 Pressure transducer systems have been a common source of epidemic outbreaks of nosocomial infection. From 1977 to 1987, these devices were the most common source of epidemic bloodstream infection investigated by the CDC.22 These outbreaks were prolonged (mean 11 months) and involved large numbers of patients (mean 24 patients). In each case, reusable transducers were either improperly disinfected or fitted with improperly sterilized domes. Recommendations for the proper care and use of both arterial catheters and pressure transducer systems are shown in Table 4-1.

Urinary Catheters

Urinary catheter use is the primary cause of urinary tract infections among critically ill patients. A survey of 112 medical ICUs in the National Nosocomial Infection Surveillance System found urinary tract infections to be responsible for 31% of all ICU-acquired infections, making urinary tract infections the most common nosocomial infection.23 Most of these infections are asymptomatic, but between 0.4% to 3.6% of patients with a nosocomial urinary tract infection develop a secondary bloodstream infection.24,25 Potentially modifiable risk factors for infections with urinary catheters include the use of open urinary drainage systems or breaks in closed drainage systems, prolonged or unnecessary urinary tract catheterization, and retrograde flow from collection bags into the bladder. Infection control measures for urinary catheters should include proper hand hygiene when caring for these devices and prompt removal of catheters when they are no longer needed (Table 4-2).

Respiratory Therapy Equipment and Nasogastric Tubes

Respiratory failure requiring mechanical ventilation is one of the most common indications for ICU admission. Nasogastric tubes are used often for both gastric decompression and to permit feeding of ICU patients. Both mechanical ventilation and nasogastric intubation bypass the normal mucosal defenses of the upper and lower respiratory tract, which leaves patients at risk for nosocomial sinusitis and pneumonia.

Among ICU patients, the vast majority of nosocomial pneumonias are ventilator-associated pneumonias. Ventilator-associated pneumonia is most likely the result of aspiration of contaminated oropharyngeal and gastric secretions and contaminated condensate in the ventilator circuit. Risk factors include the supine position, sedation or impaired consciousness, and reduced gastric acidity.25a Contaminated respiratory equipment has been implicated as the source of outbreaks of nosocomial pneumonia. Devices that generate aerosols, such as nebulizer reservoirs used for humidification26 and multidose medication nebulizers,27 have been associated with outbreaks caused by hydrophilic bacteria. Bronchoscopes also have been a source of nosocomial pneumonia in the ICU, usually as a result of an incomplete or compromised disinfection between procedures.28

Guidelines for the prevention of ventilator-associated pneumonia focus on proper hand hygiene when handling respiratory equipment, nursing ventilated patients in a semirecumbent position (30 to 45 degrees), and maintaining a closed ventilator circuit (Table 4-3). The use of noninvasive ventilation in selected ICU patients results in a lower risk of nosocomial pneumonia when compared with endotracheal mechanical ventilation. In a randomized, clinical trial, patients ventilated noninvasively had a significantly lower rate of both pneumonia (3% versus 25%) and sinusitis (0% versus 6%).29 Subglottic suctioning of oropharyngeal secretions using a specially designed endotracheal tube has been shown to reduce the incidence of ventilator-associated pneumonia and holds promise as another method to reduce the risk of nosocomial pneumonia among ventilated patients.30

The presence of a foreign body in the nasopharynx, such as a nasogastric feeding tube, predisposes to upper airway infections, particularly sinusitis. Nosocomial sinusitis is often difficult to diagnose. First, the classic signs and symptoms of sinusitis (i.e., sinus tenderness, pain, and fever) often are masked in the intubated and sedated patient. Also, sinus aspiration to determine if a sinus fluid collection is infected is performed only rarely. In a prospective study, paranasal sinus computed tomographic (CT) scans were obtained on all ICU patients with purulent nasal discharge and fever not attributable to another source, followed by sinus aspiration and culture of any fluid observed on CT scan.31 Using this method, sinusitis was identified in 7.7% of patients. Risk factors for nosocomial sinusitis include nasotracheal intubation, feeding via nasogastric tube, and impaired mental status. These infections frequently are polymicrobial, with Pseudomonas aeruginosa and Staphylococcus aureus being the most common organisms identified.31,32 Prevention involves avoiding nasotracheal intubation, placing feeding tubes through the mouth rather than through the nose, and minimizing sedative use.

Intracranial Pressure Monitoring Devices

Several infectious complications can result from the use of intracranial pressure monitoring devices, including scalp exit-site and tunnel infections, osteomyelitis of the calvarium, meningitis, and ventriculitis. The rate of infectious complications has been reported at 7.4% to 14.1% per procedure.33,34 Intracerebral or intraventricular hemorrhage, cerebrospinal fluid leaks, open head injuries, monitors in place for greater than 5 days, breaks in the pressure transducer system, and use of intraventricular versus intraparenchymal monitors have been associated with increased risk of infection. Coagulase-negative Staphylococcus spp. are the most common cause of intracranial pressure monitor–related infections, but gram-negative bacilli, such as Acinetobacter baumannii, Klebsiella pneumoniae, and Proteus mirabilis, have been reported in up to 50% of cases.35 The role of prophylactic antibiotic therapy is unclear. Several cohort studies showed no impact on the incidence of infection among patients who received antibiotics during or after insertion of the devices,34,36 but no randomized, controlled trials of sufficient sample size exist to address the question.

Interventions designed to reduce nosocomial infections typically focus on device-related infection, are evidence-based, and often employ physician and nursing education or introduce a change in the process of care. An intervention consisting of a self-study module on risk factors for catheter-associated infections, a pre- and posttest assessment of knowledge, posters and handouts on the infection control practices related to central venous catheters, and didactic teaching were given to the nursing staff of a surgical ICU.19 The authors reported a 66% reduction in the incidence of ICU-acquired bloodstream infections in the 18-month period after the intervention compared with the 18 months preintervention (p <0.001), without a significant change in the patient population. This study demonstrates that focused intervention in ICUs can reduce nosocomial infections, possibly through changes in ICU practice and staff behavior.

Another practice designed to prevent nosocomial infection is selective digestive decontamination. The hypothesis behind this practice is that colonization of the oropharynx and gastrointestinal tract by flora acquired while a patient is in the ICU serves as a source of nosocomial infection, particularly in patients requiring prolonged ICU stays and mechanical ventilation. By administering oral, nonabsorbable antibiotics, selective digestive decontamination seeks to prevent the overgrowth of gram-negative aerobic bacteria and yeast while maintaining anaerobic flora. The method has been useful in controlling outbreaks of resistant gram-negative bacteria.37 Studies of its routine use have had conflicting results, with more methodologically rigorous studies tending to show no benefit in terms of preventing nosocomial pneumonia or mortality.38,39 These observations, plus the concern of selective digestive decontamination leading to increased antibiotic resistance, leave the role of this practice unclear.

Intensive care units have long been associated with an increased prevalence of antibiotic-resistant organisms compared with other areas of the hospital. The frequent use of broad-spectrum antibiotics, a patient population with prolonged lengths of stay and the need for invasive devices, and the close interactions between health care workers and critically ill patients all contribute to the propagation of antibiotic-resistant microorganisms within the ICU. The recent emergence of highly resistant virulent organisms, such as vancomycin-resistant S. aureus, highlights the importance of understanding and controlling antibiotic resistance within the ICU.

The Epidemiology of Antibiotic Resistance

The resistant organisms seen most commonly in the ICU include methicillin-resistant S. aureus (MRSA), vancomycin-resistant Enterococcus faecium or E. faecalis (VRE), and multi-drug–resistant gram-negative bacilli, such as P. aeruginosa, Stenotrophomonas maltophilia, and extended-spectrum β-lactamase–producing Enterobacteriaceae. While each of these organisms has individual differences that affect how it is transmitted in the ICU, patients who are colonized or infected with these organisms tend to share common characteristics (Table 4-4).

Patients either can enter the ICU with endogenous resistant bacteria already present or can become colonized during their ICU stay owing to cross-contamination from other colonized patients. Bruin-Buisson and colleagues40 demonstrated through serial rectal swabs that 90% of all patients subsequently found to be colonized with multi-drug–resistant Enterobacteriaceae were negative on admission to a medical ICU and had a mean time to colonization of 14 days.40 The primary mechanism by which patient-to-patient transmission of resistant microorganisms occurs within the ICU is on the hands of health care workers. Resistant bacteria can be carried on health care workers' hands and clothing.41 Another source of transmission of antibiotic-resistant microorganisms is the ICU environment itself. This is particularly true for hydrophilic gram-negative bacilli, such as Pseudomonas spp., Stenotrophomonas spp., and Acinetobacter spp., as well as VRE. These organisms are particularly resistant to the effects of drying; therefore, they can survive on inanimate objects in the environment for extended periods of time. Outbreaks of nosocomial infections associated with these bacteria can persist if the environmental source is not addressed.42

Surveillance

Understanding the extent to which ICU patients are colonized or infected with antibiotic-resistant microorganisms is important for identifying outbreaks or high endemic rates of particular pathogens and targeting methods for control. Strategies include both passive and active surveillance. Passive surveillance is employed most frequently in ICUs within the United States and consists of identifying patients colonized with resistant microorganisms by review of clinical specimens. While this strategy requires the least amount of labor and supplies, it fails to identify a significant proportion of colonized patients.43 In active surveillance, cultures are obtained for the specific purpose of identifying colonized patients. These cultures can be performed on every patient or on selected high-risk subsets (see Table 4-4). Selective screening of high-risk patients, combined with other infection control interventions, reduced the prevalence of ICU-acquired MRSA infections in a medical ICU and was cost-effective.44 Whether this approach is cost-effective for ICUs to use for other pathogens is an area of further study.

Antibiotic Use and Control

Inadequate initial antibiotic therapy of infections has been associated with increased mortality among ICU patients. This observation argues for the use of broad-spectrum antibiotics. However, the increasing use of broad-spectrum antibiotics has been associated with the acquisition of antibiotic-resistant pathogens. Exposure to broad-spectrum antibiotics can alter the normal flora of patients and can facilitate colonization with resistant organisms or expansion of populations of already-existing organisms. The dilemma created by these competing pressures has shaped efforts to control the use of antibiotics within the ICU, particularly drugs with a broad-spectrum of activity.

Antibiotic use in the ICU can be divided into empirical use against a suspected community-acquired or nosocomial infection, targeted use against a specific pathogen, and prophylactic use. There is considerable overlap between these concepts. For example, critically ill patients often are started empirically on broad-spectrum antibiotics and then switched to an antibiotic with a more targeted spectrum once the pathogen causing infection is known. Selective digestive decontamination as a method to prevent nosocomial infections is an example of the prophylactic use of antibiotics in the ICU, which was discussed earlier in this chapter. Strategies that have been applied to control antibiotic use include closed or restricted pharmacy formularies, rapid narrowing of antibiotic spectrum of activity once a pathogen is known, discontinuation of empirical antibiotic therapy based on set clinical parameters, cycling or rotation of empirical antibiotics with gram-negative activity, and decision-support systems for physician prescribing.

Often, antibiotic therapy that is started empirically in a critically ill patient is continued even after evidence suggests that infection is not present. In a study by Singh and colleagues,45 patients suspected of having ventilator-associated pneumonia were scored using a validated clinical pulmonary infection score. Patients suspected clinically to be at risk for pneumonia but not meeting a predetermined threshold score were randomized to two groups. The experimental group received a single antibiotic for 3 days, with re-evaluation at that time. If this group still did not meet the threshold criteria, antibiotics were discontinued. The type and duration of antibiotic used in the control group were at the treating physicians' discretion. Antibiotic use was continued after 3 days in only 28% of the experimental group versus in 90% of the controls (p <0.001). Mortality and ICU length of stay did not differ between the two groups, but compared with controls, patients in the experimental group had significantly shorter durations of antibiotic use and a lower incidence of antimicrobial-resistant isolates and nosocomial infections during their ICU stay. This study suggests that basing decisions to discontinue antibiotic therapy on formal clinical criteria is an effective and safe method of reducing antibiotic use and resistance.

Cycling empirical antibiotics usually requires the use of only a single antibiotic for the empirical treatment of suspected nosocomial infection, followed by a switch to another agent after a predetermined time period. Raymond and colleagues46 compared a period of non-protocol–driven antibiotic prescribing with a set quarterly empirical antibiotic rotation and demonstrated a reduction in the occurrence of infections owing to resistant gram-negative and gram-positive bacteria along with a significant reduction in mortality owing to infection during the rotation period. While antibiotic cycling appears promising, questions remain regarding the impact that this strategy has on bacteria with multi-drug–resistant plasmids and its applicability outside of a research setting.

Increased interest in computer-assisted physician order entry has allowed for the development of physician ordering support systems. A prospective study of a computerized antibiotic management program in one ICU found that patients treated using the computerized support system had a lower incidence of mismatches between antibiotics prescribed and the susceptibility of isolated bacteria.47 The computerized support system also was associated with shorter durations of antibiotic use. Further studies need to be performed to see if the reduction in overall antibiotic use by this method can reduce the prevalence of antibiotic-resistant bacteria.

Proper hand hygiene has been known to be fundamental in preventing nosocomial infections since the studies of puerperal fever by Semmelweis in the mid-nineteenth century. After contact with patients, health care workers' hands can become transiently colonized with pathogenic and antibiotic-resistant bacteria, which are then transferred to other patients. Hand soaps containing an antiseptic agent, such as chlorhexidine, or alcohol-based hand rubs have been shown to effectively reduce bacterial counts on hands when used properly.

Despite the known benefit of proper hand hygiene in preventing nosocomial infections and the transmission of antibiotic-resistant bacteria, observed compliance with hand hygiene among ICU personnel is poor, typically between 22% and 40% for each episode of patient contact.48,49 The greatest barriers to compliance with hand hygiene are time and accessibility. An outbreak of Enterobacter cloacae infections in a neonatal ICU coincided with a period of patient overcrowding and short staffing of nurses.50 During this time, adherence to hand hygiene was 25% and subsequently increased to 70% when staffing and patient census returned to normal levels. Accessibility to sinks in the ICU is often limited, particularly in older units. When personnel do wash their hands with antiseptic soap, it is often for a shorter period of time than the duration used to test the product's effectiveness.

Waterless alcohol-based hand rubs improve health care workers' compliance with hand hygiene in the ICU.51 Compared with using traditional antiseptic soap and water, alcohol-based products require less time to use and are more convenient. Antiseptic soap and water should still be used, however, when hands are visibly soiled.

Other recommendations for ICU personnel concerning proper hand hygiene include avoiding the wearing of artificial fingernails owing to high periungual bacterial counts and outbreaks of nosocomial infections associated with these products, washing hands before and after using gloves, and providing staff with hand lotions to minimize the risk of irritant contact dermatitis.

Health care workers in the ICU are potentially at risk of being exposed to infectious agents during the course of caring for patients. Likewise, the same health care workers potentially can spread infectious agents, particularly antibiotic-resistant bacteria, to patients. A primary goal of infection control is to prevent both. Transmitting infectious agents in the ICU currently is prevented by what has been termed by the CDC as standard precautions and transmission-based precautions (i.e., airborne, droplet, and contact precautions).52

Standard Precautions

The concept of standard precautions arose primarily from attempts to prevent patient-to-health-care-worker transmission of blood-borne pathogens, particularly HIV. The concept of standard precautions is based on the assumption that all body substances (i.e., blood and other body fluids, secretions, and excretions) and certain body sites (e.g., nonintact skin and mucous membranes) are potential sources of infectious agents. Therefore, health care workers should use the same basic precautions, regardless of whether a patient is known to have a particular infection. Standard precautions are designed to minimize the risk of transmission of both recognized and unrecognized sources of infection in hospitals and include (1) wearing clean gloves when there is the potential for contact with blood, body fluids, secretions, excretions, contaminated items, mucous membranes, or nonintact skin, (2) washing hands immediately after gloves are removed or when body fluids are inadvertently contacted, (3) wearing a gown, mask, and eye protection or a face shield when there is the potential for splashing or spraying with bodily substances, (4) avoiding practices that increase the risk of exposures and injuries, such as recapping or removing used needles from syringes.

Transmission-Based Precautions

A change in the CDC guidelines in the mid-1990s was the elimination of multiple levels of isolation categories found in previous recommendations and a simplification of isolation precautions based on what is currently known of the modes of transmission of either highly contagious or epidemiologically significant pathogens (Table 4-5). Institution of transmission-based isolation for an ICU patient should occur when infection or carriage of one of these pathogens is either confirmed or suspected. Transmission-based categories of isolation include airborne, droplet, and contact isolation.52 The transmission-based isolation precautions require that patients be placed in either a private room or be cohorted with patients who have the same infection, if necessary. Transport of the patient out of the room should be limited to procedures that are medically necessary and cannot be performed in the room. When patients must be transported out of the room, the area receiving the patient should be notified of their isolation status, and special precautions (such as a surgical mask being placed on the patient for airborne and droplet precautions) should be taken to minimize infection risk during transport.

Airborne precautions are for agents transmitted by airborne droplet nuclei (generally less than 5 μm in size) or other similarly sized particles. These small particles can remain suspended in the air currents in a room for hours and may be dispersed widely. Examples of pathogens spread in this manner include Mycobacterium tuberculosis and rubeola virus. Patients with an infection caused by a pathogen transmitted via airborne particles should be housed in a private room that has negative-pressure ventilation or other special air handling relative to the outside hallway. In addition, susceptible persons who enter the room should wear an N95 respirator or other respiratory equipment capable of filtering small airborne particles; a standard surgical mask is not protective. Negative-pressure systems and other special air handling systems should be tested regularly to ensure that they function properly.

Droplet precautions are for infectious agents that are spread by larger respiratory droplets that can be generated during coughing, sneezing, talking, or performing procedures. These larger droplets do not remain suspended in the air and travel only short distances, usually 1 m or less. Examples of pathogens transmitted primarily via large respiratory droplets include influenza virus and Neisseria meningitidis. Patients who are known or suspected to be infected with an agent spread by large respiratory droplets should be placed in a private room, and all individuals should wear a surgical mask (at least) when entering within 1 m of the patient (for practical purposes, most hospitals require a mask when entering the patient's room).

Contact precautions should be employed for agents capable of spread through direct contact with the patient or contact with contaminated environmental surfaces or equipment. This is the most frequently employed transmission-based precaution in the ICU setting, typically used to prevent the spread of antibiotic-resistant bacteria. Contact precautions generally are defined as the use of gloves by all personnel entering the patient's room and the use of a gown when contact with the patient or environmental surfaces is anticipated. The use of dedicated equipment (e.g., stethoscopes, thermometers) is recommended to prevent this equipment from transmitting the infectious agent to others. Equipment should be cleaned and disinfected properly before it is used on other patients. The risk of nosocomial transmission of MRSA in a neonatal ICU was reduced 16-fold by the use of contact precautions.53 Once the patient on contact precautions is discharged from a room, environmental surfaces must be cleaned thoroughly to eliminate organisms that might persist.

Occupational Health and the ICU

Occupational or employee health plays an important role in preventing the spread of highly infectious agents among health care workers. The hospital's occupational health department is responsible for screening employees for contagious diseases and offering employees vaccination for preventable infections related to health care, particularly hepatitis B virus and varicella-zoster virus. In the case of an exposure to an infectious agent from a patient, occupational health's role is to evaluate and, if necessary, treat exposed employees. For particular infectious agents, such as exposure of a nonimmune health care worker to varicella-zoster virus, occupational health has the authority to remove a worker from direct patient care. In smaller hospitals, often a single individual will be responsible for both infection control and occupational health, but most large hospitals have two separate departments. The role of infection control is to determine which health care workers were exposed to a contagious agent and refer exposed workers to occupational health for follow-up.

Severe Acute Respiratory Syndrome (SARS)

The recent experience with the spread of infection related to a corona virus producing a severe form of the acute respiratory distress syndrome (ARDS) with significant morbidity and mortality has highlighted the challenges presented by emerging infectious diseases requiring controlling exposures in the health care environment by rapidly implementing effective infection control measures.^2288584 The outbreak of this viral illness in 2003 resulted in infection in more than 8000 people and more than 900 deaths. SARS is predominantly a respiratory illness, spread by large droplets which are inspired, and possibly by the fecal-oral route as well. Important lessons from the experience with outbreaks in Taiwan and Toronto include early identification of the epidemic, institution of strict isolation and control measures, careful screening of health care workers and others exposed to active cases, quarantine of individuals early in the course of the epidemic, and limitation of exposures to high risk interventions in the intensive care unit such as intubations or other airway manipulations. Effective responses to outbreaks such as this, which are predicted to increase in our complex and interconnected world, can only be achieved by a high degree of integration of critical care clinicians, infection control staff, and public health officials. Anticipating such problems and working to solutions in advance is a better approach than attempting to implement solutions ad hoc.

Blood-Borne Pathogens: HIV, Hepatitis C Virus, and Hepatitis B Virus

Because of the need for frequent invasive procedures, the often-urgent nature of these procedures, and the patient population that is served, critical care personnel are at risk of exposure and infection with blood-borne pathogens. The most common mechanism by which ICU personnel are exposed is by a percutaneous injury, usually an inadvertent needle stick. The risk of infection after a percutaneous exposure varies significantly depending on the virus. The risk of infection with HIV after a percutaneous exposure to infected blood or bloody fluids has been estimated to be 0.3%. The risks associated with occupational mucous membrane and cutaneous exposures to HIV-infected blood appear to be substantially smaller. For hepatitis C virus, the risk of infection after percutaneous exposure is between 0% and 7%, and for hepatitis B virus, the risk of developing serologic evidence of infection in a nonimmune person is 23% to 62%, depending on whether the source patient is positive for the hepatitis B e antigen.54

Infection control efforts against these viruses focus primarily on preventing exposure to blood and, in the case of hepatitis B virus, offering vaccination on employment. Practices that minimize the risk of percutaneous injury (e.g., discarding disposable sharp devices in puncture-resistant containers immediately after use) are key aspects of prevention. Precautions also should be applied to other body fluids containing visible blood and to cerebrospinal, synovial, pleural, peritoneal, pericardial, and amniotic fluids and vaginal secretions and semen.55 Protective equipment (i.e., gloves, gowns, masks, and eyewear) should be used when there is a potential for exposure to these fluids. Following an exposure, the affected skin should be cleaned immediately with soap and water, and mucous membranes should be rinsed with copious amounts of water. Zidovudine chemoprophylaxis following needle-stick exposure to HIV-1 decreases transmission risk by 80%.56 Current guidelines recommend 4 weeks of combination antiretroviral therapy with either a two- or three-drug regimen for postexposure prophylaxis, taking into consideration degree of exposure, level of viremia in the source patient, and the potential for resistant virus. For hepatitis C virus, no prophylaxis is currently available; exposed workers generally are monitored for 6 months for evidence of infection. For hepatitis B virus exposure, the immune status of the employee should be determined, and hepatitis B immunoglobulin and vaccination should be offered to nonimmune employees.

Varicella-Zoster Virus

Patients with evidence of disseminated varicella-zoster virus (VZV) infection (e.g., chickenpox, varicella pneumonia, disseminated zoster) or immunocompromised patients with localized zoster are capable of transmitting VZV via respiratory droplets and shedding virus from noncrusted skin lesions. These patients should be placed on airborne precautions with negative-pressure ventilation and contact precautions until all skin lesions are crusted. Immunocompetent hosts with localized zoster can be cared for using standard precautions. Health care workers without a history of chickenpox or documented evidence of immunity should not enter the room of a patient with an active VZV infection. If a potentially nonimmune health care worker or patient is exposed, VZV serology should be obtained on that individual. Seronegative personnel should be removed from direct patient contact between 10 to 21 days after the exposure occurred. Likewise, if a seronegative patient is exposed to a patient with VZV infection, he or she should be placed in the appropriate precautions between 10 and 21 days after the exposure. The use of VZV vaccine and varicella-zoster immunoglobulin should be considered in both nonimmune exposed ICU patients and personnel when not contraindicated.

Tuberculosis

Tuberculosis is frequently unsuspected in hospitalized patients, including those admitted to ICUs. This failure of diagnosis has emerged as an important contributor to mortality57 and also may increase the risk of transmission to hospital personnel. ICU personnel who perform procedures that generate respiratory aerosols (e.g., endotracheal intubation, fiberoptic bronchoscopy, and ventilator management) may be at particular risk for acquisition of tuberculosis. It should be noted that a negative acid-fast smear does not eliminate the possibility of transmission to medical personnel. ICU physicians must maintain a high level of suspicion for tuberculosis and initiate airborne precautions whenever the diagnosis is considered. Health care workers must wear National Institute of Occupational Safety and Health (NIOSH)–approved 95% (N95) particulate respirator masks or high-efficiency particulate air (HEPA)–filtered respirator masks when caring for patients with known or suspected tuberculosis.58 In addition, all ICU personnel should undergo tuberculin skin testing on hire and at regular intervals.

Respiratory Syncytial Virus

Respiratory syncytial virus (RSV) is a leading cause of bronchiolitis and pneumonia in infants and small children and is a frequent cause of nosocomial outbreaks of lower respiratory tract infections in pediatric wards. While RSV has been long recognized as a cause of seasonal infection in children, transmission has been reported in adult patients, with significant morbidity and mortality in immunocompromised hosts.59 The primary mode of transmission of RSV is inoculation of the eyes and nasal mucosa by the hands after handling objects or touching surfaces contaminated by respiratory secretions. Infants have been shown to shed high titers of RSV in respiratory secretions for up to several weeks, and the virus is stable in the environment for up to 24 hours. Health care workers in pediatric wards have been infected themselves and have transmitted the virus to other patients via contaminated hands or equipment. Infection control measures for RSV include placing infected young children, infants, and immunocompromised adults on contact precautions. Personnel with respiratory illnesses during RSV outbreaks should not care for children and immunocompromised adults at risk for severe RSV infection.60

Meningococcus

Patients with meningitis and bacteremia caused by N. meningitidis frequently require admission to the ICU for circulatory collapse and airway management. Often the diagnosis is suspected but not confirmed until the organism is isolated in culture. Patients with known or suspected meningococcal infection should be handled using droplet precautions because this organism typically is carried in the nasopharynx and spread by large respiratory droplets. Personnel should wear a surgical mask when caring for infected patients and either goggles or a face shield when performing procedures capable of generating droplets. Precautions can be discontinued after the patient has been on effective antibiotic therapy for at least 24 hours.

The admission of a patient with suspected or known meningococcal disease can generate a significant amount of anxiety among personnel. Cases of meningococcal nosocomial infection in health care workers have been associated with close contact with respiratory secretions without the use of precautions.61 However, transmission resulting in disease in health care workers is rare, and the risk of transmission from casual contact with a patient is likely negligible. The incubation period for meningococcal disease after exposure can range between 2 to 10 days but is commonly 3 to 4 days; therefore, whether antibiotic prophylaxis is warranted does not need to be determined emergently. Infection control and occupational health staff should evaluate all potential employee exposures, educate staff on the risk of infection, and determine if antibiotic prophylaxis is needed on a case-by-case basis.