Epidemiology and control of nosocomial infections in adult intensive care units

A reappraisal of the role of Gram's stains of tracheal aspirates in guiding antibiotic selection in the surgical intensive care unit

BACKGROUND

Tracheal aspirate Gram's stains are used to guide antibiotic selection in empiric pneumonia treatment in the surgical intensive care unit (SICU). We questioned whether Gram's stains predict the organism cultured.

METHODS

A retrospective review of prospectively collected data.

RESULTS

Gram's stains correlated with the cultured organism in 284 of 543 (52%) SICU cultures and in 226 of 403 (56%) trauma intensive care unit (TICU) cultures. Gram-negative rod (GNR) stains yielded GNR organisms in 182 of 205 (89%) SICU cultures and in 160 of 176 (91%) TICU cultures. Gram-positive coccus (GPC) stains yielded GPC organisms in 75 of 228 (33%) SICU cultures and in 52 of 149 (35%) TICU cultures. Noncorrelates in the GPC group were predominantly GNRs (185 of 250 (74%)).

CONCLUSION

When the clinical decision has been made that empiric antibiotic coverage is necessary, GNR coverage should be instituted regardless of Gram's stain result. The decision to institute GPC coverage needs to be supported by clinical data other than the Gram's stain.

Magnitude and prevention of nosocomial infections in the intensive care unit

Nosocomial infections among intensive care unit (ICU) patients usually are related to the use of invasive devices (e.g., mechanical ventilators, urinary catheters, or central venous catheters). This article discusses the impact of these devices and other risk factors for nosocomial infection in ICU patients. Data on etiologic pathogens and device-related infection rates from the National Nosocomial Infection Surveillance System are presented, general infection control guidelines for ICUs are reviewed, and special infection control problems encountered in ICUs are discussed.

Enterobacter spp.: pathogens poised to flourish at the turn of the century

Knowledge of the genus Enterobacter and its role in human disease has expanded exponentially in recent years. The incidence of infection in the hospital and the community has increased. New clinical syndromes have been recognized. Enterobacter spp. have also been implicated as causes of other syndromes that traditionally have been associated almost exclusively with more easily treatable pathogens, such as group A streptococci and staphylococci. Rapid emergence of multiple-drug resistance has been documented in individual patients during therapy and in populations and environments with strong selective pressure from antimicrobial agents, especially the cephalosporins. Therapeutic options for patients infected with multiply resistant strains have become severely limited. Carbapenems or, alternatively, fluoroquinolones are the most predictively active options, although resistance to both classes has been observed on rare occasions. Enterobacter spp. appear well adapted for survival and even proliferation as the turn of the century approaches.

Colonization with antibiotic-resistant gram-negative organisms in a pediatric intensive care unit

OBJECTIVE

To measure the prevalence of colonization with antibiotic-resistant Gram-negative organisms and its association with potential risk factors, including antibiotic exposure, in a pediatric intensive care unit (ICU).

DESIGN

Prospective, observational study.

SETTING

A 16-bed tertiary care pediatric ICU.

PATIENTS

All children admitted to the pediatric ICU for > 24 hrs over a 5-month period.

MEASUREMENTS AND MAIN RESULTS

Two hundred ninety-six patients, approximately half of all patients admitted to the ICU, were enrolled in the study; 236 patients had sufficient data collected for analysis and were prospectively examined for nasopharyngeal and gastrointestinal colonization by antibiotic-resistant Gram-negative organisms (ceftazidime minimal inhibitory concentration of > 16 micrograms/mL, or tobramycin minimal inhibitory concentration > 8 micrograms/mL). Association between colonization and potential predisposing factors including demographics, diagnosis, Pediatric Risk of Mortality (PRISM) score, invasive instrumentation, and prior ICU antibiotic exposure was assessed. More than 20% of patients were found to be colonized with an antibiotic-resistant Gram-negative organism. Examination of the timing of colonization indicated that more than half were identified within 72 hrs of admision. Colonization was associated by unadjusted analysis to prior ICU antibiotic exposure, as well as by factors associated with the severity of illness (PRISM score and invasive instrumentation) and young age. However, when the independence of these factors was tested by logistic regression, prior antibiotic exposure was no longer associated with resistant organism colonization.

CONCLUSIONS

These data suggest that antibiotic-resistant Gram-negative organisms are a significant risk to intensively III children and that in many instances, they are imported into the unit or rapidly acquired from environmental reservoirs. Since risk factors for colonization are multiple, policies confined to antibiotic utilization within the ICU may have fixed, and possibly limited, benefit in their control.

Risk factors for nosocomial infections caused by gram-negative bacilli. The Hellenic Antibiotic Resistance Study Group

Two hundred and ninety-nine Gram-negative hospital-acquired infections from 257 patients, consecutively identified during one month (November 1992) in five hospitals in the greater Athens area, were divided into four groups on the basis of the bacterium isolated: Group 1 (Escherichia coli group) included infections owing to E. coli, Group 2 (Proteus group) consisted of infections owing to Proteus spp. and Providencia spp., Group 3 (Kiebsiella/Enterobacter group) involved infections owing to Kiebsiella spp., Enterobacter spp., Citrobacter spp. and Serratia spp. Infections owing to Pseudomonas spp. and other non-fermenters were allocated into Group 4 (non-fermenters group). The four groups were studied in relation to risk factors including the duration of hospitalization, type of ward, underlying disease, history of operation, medical procedures/devices and antimicrobial therapy. A stepwise multiple logistic regression technique (SPSS Inc) was used to analyse the data, and the three groups (the Proteus group, the Klebsiella/Enterobacter group and the non-fermenters group) were analysed separately against the E. coli group. Infections with the Kiebsiella/Enterobacter group were associated with: (a) length of hospital stay before the infection, (b) treatment with newer antibiotics, and (c) hospitalization in an intensivecare unit (ICU). Infections with non-fermenters were associated with: (a) length of hospital stay before infection, (b) a urinary catheter, (c) type of disease (chronic infection being negatively associated), (d) treatment with newer antibiotics and (e) hospitalization in an ICU. Proteus group infections were associated with (a) length of hospital stay before infection, (b) treatment with newer antibiotics and (c) operation during present hospitalization (negative association). Interestingly, no specific hospitals were identified as risk factors. Identification of patients at risk for acquiring an infection owing to a nosocomial pathogen is vital in the development of a preventive strategy for hospital-acquired infections.

Infection control practices in intensive care units of 14 European countries. The EURO.NIS Study Group

OBJECTIVE

To evaluate compliance with recommended patient-care practices for the prevention of hospital-acquired infections (HAI) in the intensive care unit (ICU).

DESIGN

European descriptive survey by questionnaire mailed to all the directors of ICUs.

PATIENTS AND PARTICIPANTS

A total of 1642 general ICUs with more than three beds in 14 countries were contacted; 1005 units participated in the study (overall response rate of 61.2%).

MEASUREMENTS AND RESULTS

Data on the general characteristics of the hospital and of the ICU, surveillance activities, and patient-care practices relevant to the control of HAIs were collected. Compliance varied significantly by the type of practice evaluated. Comprehensive programs adopting all the recommended preventive practices for specific infections were maintained in a very low proportion of units, ranging from 18% for antibiotic policy to 39% for urinary tract infections. Moreover, 14% of the units claimed to adopt three or more practices that are clearly unsafe, and only 35% of the units claimed not to adopt any risky practice. The presence of an infection control nurse was significantly associated with a lower frequency of substandard care. A great variability was observed by country in the adoption of 29 patient-care practices, mostly for practices for which clear-cut guidelines are lacking.

CONCLUSION

Interpretation of data is made difficult by the lack of consensus among experts with respect to some of the practices investigated. Nevertheless, the implementation of standard practices for preventing HAIs is far from satisfactory in the hospitals surveyed, even in a high priority hospital area such as intensive care. Documented European guidelines could be worth-while in increasing awareness of the ICU staff. The availability of at least one infection control nurse in each hospital should be strongly advocated.

Postoperative infections traced to contamination of an intravenous anesthetic, propofol

BACKGROUND

Between June 1990 and February 1993, the Centers for Disease Control and Prevention conducted investigations at seven hospitals because of unusual outbreaks of bloodstream infections, surgical-site infections, and acute febrile episodes after surgical procedures.

METHODS

We conducted case-control or cohort studies, or both, to identify risk factors. A case patient was defined as any patient who had an organism-specific infection or acute febrile episode after a surgical procedure during the study period in that hospital. The investigations also included reviews of procedures, cultures, and microbiologic studies of infecting, contaminating, and colonizing strains.

RESULTS

Sixty-two case patients were identified, 49 (79 percent) of whom underwent surgery during an epidemic period. Postoperative complications were more frequent during the epidemic period than before it. Only exposure to propofol, a lipid-based anesthetic agent, was significantly associated with the postoperative complications at all seven hospitals. In six of the outbreaks, an etiologic agent (Staphylococcus aureus, Candida albicans, Moraxella osloensis, Enterobacter agglomerans, or Serratia marcescens) was identified, and the same strains were isolated from the case patients. Although cultures of unopened containers of propofol were negative, at two hospitals cultures of propofol from syringes currently in use were positive. At one hospital, the recovered organism was identical to the organism isolated from the case patients. Interviews with and observation of anesthesiology personnel documented a wide variety of lapses in aseptic techniques.

CONCLUSIONS

With the increasing use of lipid-based medications, which support rapid bacterial growth at room temperature, strict aseptic techniques are essential during the handling of these agents to prevent extrinsic contamination and dangerous infectious complications.

Central venous catheter-related infections: pathogenesis, predictors, and prevention

Central venous catheters are used widely for a variety of therapeutic purposes and have an increased incidence of infections related to their use. The purpose of this article is to address the issue of central venous catheter-related infections, including pathogenesis, predictors and diagnosis, and prevention.

Prophylaxis with enteral antibiotics in ventilated patients: selective decontamination or selective cross-infection?

Selective decontamination of the digestive tract (SDD) has been evaluated as a method to prevent colonization and infection in ventilated patients in 40 trials. On the basis of an assumption that cross-infection would be reduced as a consequence of SDD and that this would distort the results of SDD studies that used concurrent controls, 14 studies used historic controls. To test this assumption, three observations from the two types of studies were compared. (i) The differences between observed and expected event rates for each study were used to perform a meta-analysis. This revealed that the summary odds ratios for bacteremia and respiratory infection were marked by significant heterogeneity (P > 0.95) and inconsistencies between those derived from studies with concurrent versus studies with historic controls. (ii) Where the data were available, the rates of acquisition of colonization in control groups were higher in studies with concurrent controls than in studies with historic controls. (iii) At least four studies with concurrent controls have shown a pattern of pathogenic isolates consistent with cross-infection between groups. These results are contrary to the initial assumption and suggest the possibility that SDD represents a major cross-infection hazard.

Epidemiology of nosocomial infections in adult intensive care units

Patients in intensive care units (ICUs) are a small subgroup of all hospitalized patients, but they account for approximately 25% of all hospital infections. Nosocomial infection rates among ICU patients are 5-10 times higher than among general ward patients. ICU infection rates are higher due to complex interactions between the patients' underlying disease, severity of illness, type of ICU, duration of stay, and invasive devices used. Antimicrobial resistance is a major clinical problem despite potent and newer antibiotics. Organisms that pose a clinically significant resistance problem among ICU patients include methicillin-resistant staphylococci, enterococci, a wide variety of enterobacteriaceae, Pseudomonas aeruginosa, Pseudomonas cepacia, Xanthomonas maltophila, Acinetobacter and Candida species. Traditional infection control measures include identification of reservoirs, halting transmission between patients, stopping progression from colonization to infection and modifying host risk. In addition, sound selection procedures and guidelines for antibiotic usage are necessary to control the spread of multi-resistant micro-organisms.

Risk factors for acquisition of multiply drug-resistant gram-negative bacteria

Some bacteria are naturally resistant to many antibiotics and most can become multiply resistant. Multiply resistant gram-negative bacteria have proved a particular problem over the last 30 years, but the development of new agents has lessened their significance for most clinicians. Now, however, clinical practice is threatened by the lack of new classes of antibiotics, the widespread emergence of resistance and the advent of plasmid-mediated cephalosporinases by which the spread of resistance is likely to be rapid. Increased use of prophylaxis in immunosuppressed and intensive care patients is likely to aggravate the problem, as is the use of new broad-spectrum agents in the community. More directed and restricted antibiotic use and better education of patients and prescriber are necessary to contain the problem of antibiotic resistance. Improved surveillance of sensitivity trends is essential. Many outbreaks also are associated with poor infection control techniques. The cost of outbreaks due to multiply resistant organisms and lack of compliance with infection control procedures needs to be properly studied. While many predisposing factors for the acquisition of these organisms and the development of infection are understood, the multifactorial nature of illness in many patients complicates the issue, necessitating further study of risk factors and preventative and therapeutic measures.

Serious Infections Caused by Pseudomonas Aeruginosa

Over the last 3 decades, Pseudomonas aeruginosa has become a leading cause of infectious morbidity and mortality in certain predisposed patient populations. It primarily affects those with impaired host defenses, and its prevalence in the hospital environment makes it an important nosocomial pathogen. Infection with this organism may result in a broad spectrum of clinical manifestations, many of which may be seen in the intensive care setting. This review focuses on epidemiology, clinical presentations, nad treatment of serious Pseudomonas infections.

An overview of nosocomial infections, including the role of the microbiology laboratory

An estimated 2 million patients develop nosocomial infections in the United States annually. The increasing number of antimicrobial agent-resistant pathogens and high-risk patients in hospitals are challenges to progress in preventing and controlling these infections. While Escherichia coli and Staphylococcus aureus remain the most common pathogens isolated overall from nosocomial infections, coagulase-negative staphylococci (CoNS), organisms previously considered contaminants in most cultures, are now the predominant pathogens in bloodstream infections. The growing number of antimicrobial agent-resistant organisms is troublesome, particularly vancomycin-resistant CoNS and Enterococcus spp. and Pseudomonas aeruginosa resistant to imipenem. The active involvement and cooperation of the microbiology laboratory are important to the infection control program, particularly in surveillance and the use of laboratory services for epidemiologic purposes. Surveillance is used to identify possible infection problems, monitor infection trends, and assess the quality of care in the hospital. It requires high-quality laboratory data that are timely and easily accessible.

The gastrointestinal tract. The "undrained abscess" of multiple organ failure

OBJECTIVE

This study determined the association between proximal gastrointestinal (GI) colonization and the development of intensive care unit (ICU)-acquired infection and multiple organ failure (MOF) in a population of critically ill surgical patients.

SUMMARY BACKGROUND DATA

ICU-acquired infection in association with progressive organ system dysfunction is an important cause of morbidity and mortality in critical surgical illness. Oropharyngeal and gastric colonization with the characteristic infecting species is common, but its association with ICU morbidity is poorly defined.

METHODS

A prospective cohort study of 41 surgical ICU patients was undertaken. Specimens of gastric and upper small bowel fluid were obtained for quantitative culture; the severity of organ dysfunction was quantitated by a numeric score.

RESULTS

One or more episodes of ICU-acquired infection developed in 33 patients and involved at least one organism concomitantly cultured from the upper GI tract in all but 3. The most common organisms causing ICU-acquired infection--Candida, Streptococcus faecalis, Pseudomonas, and coagulase-negative Staphylococci--were also the most common species colonizing the proximal GI tract. Gut colonization correlated with the development of invasive infection within 1 week of culture for Pseudomonas (90% vs. 13% in noncolonized patients, p < 0.0001) or Staphylococcus epidermidis (80% vs. 6%, p < 0.0001); a weaker association was seen for colonization with Candida. Infections associated with GI colonization included pneumonia (16 patients), wound infection (12 patients), urinary tract infection (11 patients), recurrent (tertiary) peritonitis (11 patients), and bacteremia (10 patients). ICU mortality was greater for patients colonized with Pseudomonas (70% vs. 26%, p = 0.03); organ dysfunction was most marked in patients colonized with one or more of the following: Candida, Pseudomonas, or S. epidermidis.

CONCLUSIONS

The upper GI tract is an important reservoir of the organisms causing ICU-acquired infection. Pathologic GI colonization is associated with the development of MOF in the critically ill surgical patient.