Page 58 - Hall et al (2015) Principles of Critical Care-McGraw-Hill

CHAPTER 4: Infection Prevention and Surveillance in the Intensive Care Unit 27

ANTIBIOTIC RESISTANCE IN THE ICU within the United States and consists of identifying patients colonized
with resistant microorganisms by review of clinical specimens. While
Intensive care units have long been associated with an increased preva- this strategy requires the least amount of labor and supplies, it fails to
lence of antibiotic-resistant organisms compared with other areas of the identify a significant proportion of colonized patients. In active sur-
64
hospital. The frequent use of broad-spectrum antibiotics, a patient popu- veillance, cultures are obtained for the specific purpose of identifying
lation with prolonged lengths of stay and the need for invasive devices, colonized patients. These cultures can be performed on every patient
and the close interactions between health care workers and critically ill or on selected high-risk subsets (see Table 4-4). Selective screening of
patients all contribute to the propagation of antibiotic-resistant microor- high-risk patients, combined with other infection control interventions,
ganisms within the ICU. The recent emergence of highly resistant virulent reduced the prevalence of ICU-acquired MRSA infections in a medi-
organisms, such as vancomycin-resistant S aureus, multidrug-resistant cal ICU and was cost effective. Published guidelines recommended
65
(MDR) gram-negative bacilli, and C difficile highlight the importance of active surveillance culture for detecting MRSA-colonized patients. 66-68
understanding and controlling antibiotic resistance within the ICU. However, a European randomized controlled study demonstrated that
■ THE EPIDEMIOLOGY OF ANTIBIOTIC RESISTANCE active surveillance for MRSA did not reduce the incidence of MRSA
infection. In a recent North American trial, targeted versus universal
69
The resistant organisms seen most commonly in the ICU include meth- decolonization to prevent ICU infection were compared in a prospective
70
icillin-resistant S aureus (MRSA), vancomycin-resistant Enterococcus randomized (by center) trial. Universal decolonization with chlorhexi-
faecium or E. faecalis (VRE), and MDR gram-negative bacilli, such as dine bathing and adjunct therapy appeared more effective at reducing
P. aeruginosa, Stenotrophomonas maltophilia, Acinetobacter baumanii, nosocomial ICU infection than MRSA-specific screening and isolation
and extended-spectrum β-lactamase–producing Enterobacteriaceae. policies. Whether this approach is cost effective for ICUs to use for other
While each of these organisms has individual differences that affect ICU pathogens is an area of further study.
transmission, patients who are colonized or infected with these organ- ■
isms tend to share common characteristics (Table 4-4). 97 ANTIBIOTIC USE AND CONTROL
Patients can either enter the ICU with endogenous-resistant bac- Inadequate initial antibiotic therapy of infections has been associated
teria already present or become colonized during their ICU stay with increased mortality among ICU patients. This observation argues
71
owing to cross-contamination from other colonized patients. Brun- for the use of broad-spectrum antibiotics. However, the increasing use
Buisson and colleagues demonstrated through serial rectal swabs that of broad-spectrum antibiotics has been associated with the acquisition
90% of all patients subsequently found to be colonized with MDR of antibiotic-resistant pathogens. Exposure to broad-spectrum antibiot-
Enterobacteriaceae were negative on admission to a medical ICU and ics can alter the normal flora of patients and can facilitate colonization
had a mean time to colonization of 14 days. The primary mechanism with resistant organisms or expansion of populations of already-existing
61
by which patient-to-patient transmission of resistant microorganisms organisms. The dilemma created by these competing pressures has
occurs within the ICU is on the hands of health care workers. Resistant shaped efforts to control the use of antibiotics within the ICU, particu-
bacteria can be carried on health care workers’ hands and clothing. larly drugs with a broad-spectrum of activity.
62
Another source of transmission of antibiotic-resistant microorganisms Antibiotic use in the ICU can be divided into empirical use against
is the ICU environment itself. This is particularly true for hydrophilic, a suspected community-acquired or health care–associated infec-
gram-negative bacilli, such as Pseudomonas spp, Stenotrophomonas tion, targeted use against a specific pathogen, and prophylactic use.
spp, and Acinetobacter spp, VRE, and C difficile. These organisms are There is considerable overlap between these concepts. For example,
particularly resistant to the effects of drying; therefore, they can survive critically ill patients often are started empirically on broad-spectrum
on inanimate objects in the environment for extended periods of time. antibiotics and then switched to an antibiotic with a more targeted
Outbreaks of health care–associated infections associated with these spectrum once the pathogen-causing infection is known. Selective
bacteria can persist if the environmental source is not addressed. 63 digestive decontamination as a method to prevent nosocomial infec-
tions is an example of the prophylactic use of antibiotics in the ICU,
PREVENTING ANTIBIOTIC RESISTANCE IN THE ICU which was discussed earlier in this chapter. Strategies that have been
applied to control antibiotic use include closed or restricted pharmacy
■ SURVEILLANCE formularies, rapid narrowing of antibiotic spectrum of activity once
Understanding the extent to which ICU patients are colonized or a pathogen is known, discontinuation of empirical antibiotic therapy
based on set clinical parameters, cycling or rotation of empirical anti-
infected with antibiotic-resistant microorganisms is important for biotics with gram-negative activity, and decision-support systems for
identifying outbreaks or high endemic rates of particular pathogens and physician prescribing.
targeting methods for control. Strategies include both passive and active Often, antibiotic therapy that is started empirically in a critically ill
surveillance. Passive surveillance is employed most frequently in ICUs patient is continued even after evidence suggests that infection is not
present. In a study by Singh and colleagues, patients suspected of hav-
72
ing ventilator-associated pneumonia were scored using a validated clini-
TABLE 4-4 Factors Associated With Colonization or Infection With Multidrug- cal pulmonary infection score. Patients suspected clinically to be at risk
Resistant Microorganisms for pneumonia but not meeting a predetermined threshold score were
• Extended length of hospitalization randomized to two groups. The experimental group received a single
antibiotic for 3 days, with reevaluation at that time. If this group still did
• Interhospital or nursing home transfer
not meet the threshold criteria, antibiotics were discontinued. The type
• Immunocompromised host and duration of antibiotic used in the control group were at the treat-
• Invasive devices (ie, central venous catheters, mechanical ventilation) ing physicians’ discretion. Antibiotic use was continued after 3 days in
• Advanced age only 28% of the experimental group versus in 90% of the control group
(p <0.001). Mortality and ICU length of stay did not differ between the
• Severity of illness two groups, but patients in the experimental group had significantly
• Exposure to broad spectrum antibiotics shorter durations of antibiotic use and a lower incidence of antimicro-
Data from Safdar N, Maki DG. The commonality of risk factors for nosocomial colonization and infection bial-resistant isolates and nosocomial infections during their ICU stay.
with antimicrobial-resistant Staphylococcus aureus, enterococcus, gram-negative bacilli, Clostridium dif- In a randomized controlled trial, the treatment efficacy was not different
ficile, and Candida. Ann Intern Med. 2002;136(11): 834-844. 97 between the patients who received either shorter or longer duration of

Section01.indd 27 1/22/2015 9:36:48 AM