The impact of antimicrobial-resistant, health care-associated infections on mortality in the United States

We used data reported from US hospitals to the National Nosocomial Infection Surveillance System of the Centers for Disease Control and Prevention for 3 specific infections: Staphylococcus aureus bloodstream infections, Pseudomonas aeruginosa pneumonias, and Escherichia coli urinary tract infections. We evaluated the proportion of infections with antimicrobial-resistant isolates and the relative risk of death associated with the resistant pathogen in the period 2000-2004, compared with the period 1990-1994. The proportion of antimicrobial-resistant infections increased, but there was no change in the relative risk of death between the 2 periods.

Secular trend of hospital-acquired candidemia among intensive care unit patients in the United States during 1989-1999

We describe the annual incidence of primary bloodstream infection (BSI) associated with Candida albicans and common non-albicans species of Candida among patients in intensive care units that participated in the National Nosocomial Infections Surveillance system from 1 January 1989 through 31 December 1999. During the study period, there was a significant decrease in the incidence of C. albicans BSI (P<.001) and a significant increase in the incidence of Candida glabrata BSI (P=.05).

Surgical site infection (SSI) rates in the United States, 1992-1998: the National Nosocomial Infections Surveillance System basic SSI risk index

By use of the National Nosocomial Infections Surveillance (NNIS) System's surgical patient surveillance component protocol, the NNIS basic risk index was examined to predict the risk of a surgical site infection (SSI). The NNIS basic SSI risk index is composed of the following criteria: American Society of Anesthesiologists score of 3, 4, or 5; wound class; and duration of surgery. The effect when a laparoscope was used was also determined. Overall, for 34 of the 44 NNIS procedure categories, SSI rates increased significantly (P< .05) with the number of risk factors present. With regard to cholecystectomy and colon surgery, the SSI rate was significantly lower when the procedure was done laparoscopically within each risk index category. With regard to appendectomy and gastric surgery, use of a laparoscope affected SSI rates only when no other risk factors were present. The NNIS basic SSI index is useful for risk adjustment for a wide variety of procedures. For 4 operations, the use of a laparoscope lowered SSI risk, requiring modification of the NNIS basic SSI risk index.

The effect of vancomycin and third-generation cephalosporins on prevalence of vancomycin-resistant enterococci in 126 U.S. adult intensive care units

BACKGROUND

Patient-specific risk factors for acquisition of vancomycin-resistant enterococci (VRE) among hospitalized patients are becoming well defined. However, few studies have reported data on the institutional risk factors, including rates of antimicrobial use, that predict rates of VRE. Identifying modifiable institutional factors can advance quality-improvement efforts to minimize hospital-acquired infections with VRE.

OBJECTIVE

To determine the independent importance of any association between antimicrobial use and risk factors for nosocomial infection on rates of VRE in intensive care units (ICUs).

DESIGN

Prospective ecologic study.

SETTING

126 adult ICUs from 60 U.S. hospitals from January 1996 through July 1999.

PATIENTS

All patients admitted to participating ICUs.

MEASUREMENTS

Monthly use of antimicrobial agents (defined daily doses per 1000 patient-days), nosocomial infection rates, and susceptibilities of all tested enterococci isolated from clinical cultures.

RESULTS

Prevalence of VRE (median, 10%; range, 0% to 59%) varied by type of ICU and by teaching status and size of the hospital. Prevalence of VRE was strongly associated with VRE prevalence among inpatient non-ICU areas and outpatient areas in the hospital, ventilator-days per 1000 patient-days, and rate of parenteral vancomycin use. In a weighted linear regression model controlling for type of ICU and rates of VRE among non-ICU inpatient areas, rates of vancomycin use (P < 0.001) and third-generation cephalosporin use (P = 0.02) were independently associated with VRE prevalence.

CONCLUSIONS

Higher rates of vancomycin or third-generation cephalosporin use were associated with increased prevalence of VRE, independent of other ICU characteristics and the endemic VRE prevalence elsewhere in the hospital. Decreasing the use rates of these antimicrobial agents could reduce rates of VRE in ICUs.

Antimicrobial resistance prevalence rates in hospital antibiograms reflect prevalence rates among pathogens associated with hospital-acquired infections

To determine whether routine antibiograms (summaries reporting resistance of all tested isolates) reflect resistance rates among pathogens associated with hospital-acquired infections, we compared data collected from 2 different surveillance components in the same 166 intensive care units (ICUs). ICUs reported data during the same months to both the infection-based surveillance and the laboratory-based surveillance. Paired comparisons of the percentage of isolates resistant were made between systems within each ICU. No significant differences existed (P>.05) between the percentage of isolates resistant from the infection-based system and laboratory-based system for all antimicrobial-resistant organisms studied, except methicillin resistance in Staphylococcus species. The mean difference in percentage resistance was higher from the infection-based system than the laboratory-based system for S. aureus (mean difference, +8%, P<.001) and coagulase-negative staphylococci (mean difference, +9%, P<.001). Overall, hospital antibiograms reflected susceptibility patterns among isolates associated with hospital-acquired infections. Hospital antibiograms may underestimate the relative frequency of methicillin resistance among Staphylococcus species when associated with hospital-acquired infections.

Ability of laboratories to detect emerging antimicrobial resistance in nosocomial pathogens: a survey of project ICARE laboratories

A proficiency testing project was conducted among 48 microbiology laboratories participating in Project ICARE (Intensive Care Antimicrobial Resistance Epidemiology). All laboratories correctly identified the Staphylococcus aureus challenge strain as oxacillin- resistant and an Enterococcus faecium strain as vancomycin-resistant. Thirty-one (97%) of 32 laboratories correctly reported the Streptococcus pneumoniae strain as erythromycin-resistant. All laboratories testing the Pseudomonas aeruginosa strain against ciprofloxacin or ofloxacin correctly reported the organism as resistant. Of 40 laboratories, 30 (75%) correctly reported resistant MICs or zone sizes for the imipenem- and meropenem-resistant Serratia marcescens. For the extended-spectrum beta-lactamase (ESBL)-producing strain of Klebsiella pneumoniae, 18 (42%) of 43 laboratories testing ceftazidime correctly reported ceftazidime MICs in the resistant range. These results suggest that current testing generally produces accurate results, although some laboratories have difficulty detecting resistance to carbapenems and extended-spectrum cephalosporins. This highlights the need for monitoring how well susceptibility test systems in clinical laboratories detect emerging resistance.

Nosocomial infections in combined medical-surgical intensive care units in the United States

OBJECTIVE

To describe the epidemiology of nosocomial infections in combined medical-surgical (MS) intensive care units (ICUs) participating in the National Nosocomial Infection Surveillance (NNIS) System.

DESIGN

Analysis of surveillance data on 498,998 patients with 1,554,070 patient-days, collected between 1992 and 1998 from 205 MS ICUs following the NNIS Intensive Care Unit protocol, representing 152 participating NNIS hospitals in the United States.

RESULTS

Infections at three major sites represented 68% of all reported infections (nosocomial pneumonia, 31%; urinary tract infections (UTIs), 23%; and primary bloodstream infections (BSIs), 14%: 83% of episodes of nosocomial pneumonia were associated with mechanical ventilation, 97% of UTIs occurred in catheterized patients, and 87% of primary BSIs in patients with a central line. In patients with primary BSIs, coagulase-negative staphylococci (39%) were the most common pathogens reported; Staphylococcus aureus (12%) was as frequently reported as enterococci (11%). Coagulase-negative staphylococcal BSIs were increasingly reported over the 6 years, but no increase was seen in candidemia or enterococcal bacteremia. In patients with pneumonia, S. aureus (17%) was the most frequently reported isolate. Of reported isolates, 59% were gram-negative bacilli. In patients with UTIs, Escherichia coli (19%) was the most frequently reported isolate. Of reported isolates, 31% were fungi. In patients with surgical-site infections, Enterococcus (17%) was the single most frequently reported pathogen. Device-associated nosocomial infection rates for BSIs, pneumonia, and UTIs did not correlate with length of ICU stay, hospital bed size, number of beds in the ICU, or season. Combined MS ICUs in major teaching hospitals had higher device-associated infection rates compared to all other hospitals with combined medical-surgical units.

CONCLUSIONS

Nosocomial infections in MS ICUs at the most frequent infection sites (bloodstream, urinary, and respiratory tract) almost always were associated with use of an invasive device. Device-associated infection rates were the best available comparative rates between combined MS ICUs, but the distribution of device-associated rates should be stratified by a hospital's major teaching affiliation status.

Practices to improve antimicrobial use at 47 US hospitals: the status of the 1997 SHEA/IDSA position paper recommendations. Society for Healthcare Epidemiology of America/Infectious Diseases Society of America

OBJECTIVE

To determine the status of programs to improve antimicrobial prescribing at select US hospitals.

DESIGN

Cross-sectional survey.

PARTICIPANTS AND SETTING

Pharmacy and infection control staff at all 47 hospitals participating in phase 3 of Project Intensive Care Antimicrobial Resistance Epidemiology.

RESULTS

All 47 hospitals had some programs to improve antimicrobial use, but the practices reported varied considerably. All used a formulary, and 43 (91%) used it in conjunction with at least one of the other three antimicrobial-use policies evaluated: stop orders, restriction, and criteria-based clinical practice guidelines (CPGs). CPGs were reported most commonly (70%), followed by stop orders (60%) and restriction policies (40%). Although consultation with an infectious disease physician (70%) or pharmacist (66%) was commonly used to influence initial antimicrobial choice, few (40%) reported a system to measure compliance with these consultations.

CONCLUSIONS

In most hospitals surveyed, practices to improve antimicrobial use, although present, were inadequate based on recommendations in a Society for Healthcare Epidemiology of America and Infectious Disease Society of America joint position paper. There is room to improve antimicrobial-use stewardship at US hospitals.

Glycopeptide-intermediate Staphylococcus aureus: evaluation of a novel screening method and results of a survey of selected U.S. hospitals

Isolates of Staphylococcus aureus with decreased susceptibilities to glycopeptide antimicrobial agents, such as vancomycin and teicoplanin, have emerged in the United States and elsewhere. Commercially prepared brain heart infusion agar (BHIA) supplemented with 6 microg of vancomycin per ml was shown in a previous study to detect glycopeptide-intermediate S. aureus (GISA) with high sensitivity and specificity; however, this medium, when prepared in-house, occasionally showed growth of vancomycin-susceptible control organisms. This limitation could significantly impact laboratories that prepare media in-house, particularly if they wished to conduct large surveillance studies for GISA. Therefore, a pilot study to detect GISA was performed with vancomycin-containing Mueller-Hinton agar (MHA) prepared in-house in place of commercially prepared BHIA. MHA was selected for this study because this medium is widely available and well standardized. The results of the pilot study showed that supplementation of MHA with 5 microg of vancomycin per ml was both a sensitive and a specific method for screening for GISA isolates. This method was used to screen for GISA among 630 clinical isolates of methicillin-resistant S. aureus collected during 1997 from 33 U.S. hospitals. Although 14 S. aureus isolates grew on the screening agar, all were vancomycin susceptible (MICs were </=1 microg/ml) by broth microdilution testing. Population analyses of five isolates revealed two with a subpopulation for which vancomycin MICs were 8 microg/ml. In summary, the MHA screen plate containing 5 microg of vancomycin per ml prepared in-house provides a sensitive and cost-effective method for large-scale screening for GISA for which vancomycin MICs are 8 microg/ml. However, confirmation of isolates as vancomycin resistant is critical. This study suggests that GISA was not a widespread problem in the United States in 1997.

Surveillance of antimicrobial use and antimicrobial resistance in United States hospitals: project ICARE phase 2. Project Intensive Care Antimicrobial Resistance Epidemiology (ICARE) hospitals

The search for the means to understand and control the emergence and spread of antimicrobial resistance has become a public health priority. Project ICARE (Intensive Care Antimicrobial Resistance Epidemiology) has established laboratory-based surveillance for antimicrobial resistance and antimicrobial use at a subset of hospitals participating in the National Nosocomial Infection Surveillance system. These data illustrate that for most antimicrobial-resistant organisms studied, rates of resistance were highest in the intensive care unit (ICU) areas and lowest in the outpatient areas. A notable exception was ciprofloxacin- or ofloxacin-resistant Pseudomonas aeruginosa, for which resistance rates were highest in the outpatient areas. For most of the antimicrobial agents associated with this resistance, the rate of use was highest in the ICU areas, in parallel to the pattern seen for resistance. These comparative data on use and resistance among similar areas (i.e., ICU or other inpatient areas) can be used as a benchmark by participating hospitals to focus their efforts at addressing antimicrobial resistance.

Antimicrobial resistance in intensive care units

The unique nature of the intensive care unit (ICU) environment makes this part of the hospital a focus for the emergence and spread of many antimicrobial-resistant pathogens. There are ample opportunities for the cross-transmission of resistant bacteria from patient to patient, and patients are commonly exposed to broad-spectrum antimicrobial agents. Rates of resistance have increased for most pathogens associated with nosocomial infections among ICU patients, and rates are almost universally higher among ICU patients compared with non-ICU patients. There are many opportunities, however, to prevent the emergence and spread of these resistant pathogens through improved use of established infection control measures (i.e., patient isolation, hand washing, glove use, and appropriate gown use), and implementation of a systematic review of antimicrobial use.

A survey of methods used to detect nosocomial legionellosis among participants in the National Nosocomial Infections Surveillance System

OBJECTIVE

To help define the scope of nosocomial legionnaire's disease (LD) and to assess use of recommended diagnostic methods and transmission control practices.

METHODS

We surveyed 253 hospitals participating in the National Nosocomial Infections Surveillance (NNIS) System. The anonymous survey included questions about episodes of nosocomial LD, environmental sampling practices, maintenance of hospital water systems, and diagnostic techniques.

RESULTS

Of 192 hospitals that responded, 29% reported at least one episode of nosocomial LD from 1990 through 1996, and 61% of these reported at least two episodes. Of 79 hospitals with transplant programs, 42% reported nosocomial LD, compared with 20% of hospitals without transplant programs. Environmental sampling had been conducted by 55% of hospitals, including 79% of those reporting nosocomial LD. Legionella were isolated in 34% that sampled potable water and 19% that sampled cooling system reservoirs. Supplemental potable-water decontamination systems were installed in 20% of hospitals. Only 19% routinely performed testing for legionellosis among patients at high risk for nosocomial LD.

CONCLUSIONS

Nosocomial LD is relatively common among NNIS hospitals, especially those performing organ transplants. Environmental sampling for Legionella is a common practice among NNIS hospitals, and Legionella often are isolated from sampled hospital cooling towers and hospital potable-water systems. Hospitals have responded to suspected nosocomial LD infection with a variety of water sampling and control strategies; some have not attempted to sample or decontaminate water systems despite identified transmission.

Determinants of vancomycin use in adult intensive care units in 41 United States hospitals

We analyzed data from a prospective observational cohort study that included 108 adult intensive care units (ICUs) in 41 United States hospitals. Use of vancomycin (defined daily doses per 1,000 patient-days), nosocomial infection rates, and proportion of all Staphylococcus aureus isolates resistant to methicillin (MRSA rate) were recorded from January 1996 through November 1997. The median rate of vancomycin use was lowest in coronary care ICUs and highest in general surgical ICUs. Prior approval before use of vancomycin was required in only 26 (24%) of the 108 ICUs. In a multivariate linear regression model, rates of MRSA, central line-associated bloodstream infection, and the type of ICU were independent predictors of vancomycin use. None of the vancomycin control practices was associated with lower rates of vancomycin use; however, it is important to recognize that this database was not designed to measure rates of inappropriate use. Vancomycin use is heavily determined by rates of endemic MRSA and central line-associated bloodstream infection. Efforts to reduce these rates through infection control activities should be included in hospitals' efforts to reduce vancomycin use.

Nosocomial infections in medical intensive care units in the United States. National Nosocomial Infections Surveillance System

OBJECTIVE

To describe the epidemiology of nosocomial infections in medical intensive care units (ICUs) in the United States.

DESIGN

Analysis of ICU surveillance data collected through the National Nosocomial Infections Surveillance (NNIS) System between 1992 and 1997.

SETTING

Medical ICUs in the United States.

PATIENTS

A total of 181,993 patients.

MEASUREMENTS AND MAIN RESULTS

Nosocomial infections were analyzed by infection site and pathogen distribution. Urinary tract infections were most frequent (31%), followed by pneumonia (27%) and primary bloodstream infections (19%). Eighty-seven percent of primary bloodstream infections were associated with central lines, 86% of nosocomial pneumonia was associated with mechanical ventilation, and 95% of urinary tract infections were associated with urinary catheters. Coagulase-negative staphylococci (36%) were the most common bloodstream infection isolates, followed by enterococci (16%) and Staphylococcus aureus (13%). Twelve percent of bloodstream isolates were fungi. The most frequent isolates from pneumonia were Gram-negative aerobic organisms (64%). Pseudomonas aeruginosa (21%) was the most frequently isolated of these. S. aureus (20%) was isolated with similar frequency. Candida albicans was the most common single pathogen isolated from urine and made up just over half of the fungal isolates. Fungal urinary infections were associated with asymptomatic funguria rather than symptomatic urinary tract infections (p < .0001). Certain pathogens were associated with device use: coagulase-negative staphylococci with central lines, P. aeruginosa and Acinetobacter species with ventilators, and fungal infections with urinary catheters. Patient nosocomial infection rates for the major sites correlated strongly with device use. Device exposure was controlled for by calculating device-associated infection rates for bloodstream infections, pneumonia, and urinary tract infections by dividing the number of device-associated infections by the number of days of device use. There was no association between these device-associated infection rates and number of hospital beds, number of ICU beds, or length of stay. There is a considerable variation within the distribution of each of these infection rates.

CONCLUSIONS

The distribution of sites of infection in medical ICUs differed from that previously reported in NNIS ICU surveillance studies, largely as a result of anticipated low rates of surgical site infections. Primary bloodstream infections, pneumonia, and urinary tract infections associated with invasive devices made up the great majority of nosocomial infections. Coagulase-negative staphylococci were more frequently associated with primary bloodstream infections than reported from NNIS ICUs of all types in the 1980s, and enterococci were a more frequent isolate from bloodstream infections than S. aureus. Fungal urinary tract infections, often asymptomatic and associated with catheter use, were considerably more frequent than previously reported. Invasive device-associated infections were associated with specific pathogens. Although device-associated site-specific infection rates are currently our most useful rates for performing comparisons between ICUs, the considerable variation in these rates between ICUs indicates the need for further risk adjustment.

Nosocomial infections in pediatric intensive care units in the United States. National Nosocomial Infections Surveillance System

OBJECTIVES

To describe the epidemiology of nosocomial infections in pediatric intensive care units (ICUs) in the United States.

BACKGROUND

Patient and ICU characteristics in pediatric ICUs suggest the pattern of nosocomial infections experienced may differ from that seen in adult ICUs.

METHODS

Data were collected between January 1992 and December 1997 from 61 pediatric ICUs in the United States using the standard surveillance protocols and nosocomial infection site definitions of the National Nosocomial Infections Surveillance System's ICU surveillance component.

RESULTS

Data on 110 709 patients with 6290 nosocomial infections were analyzed. Primary bloodstream infections (28%), pneumonia (21%), and urinary tract infections (15%) were most frequent and were almost always associated with use of an invasive device. Primary bloodstream infections and surgical site infections were reported more frequently in infants aged 2 months or less as compared with older children. Urinary tract infections were reported more frequently in children >5 years old compared with younger children. Coagulase-negative staphylococci (38%) were the most common bloodstream isolates, and aerobic Gram-negative bacilli were reported in 25% of primary bloodstream infections. Pseudomonas aeruginosa (22%) was the most common species reported from pneumonia and Escherichia coli (19%), from urinary tract infections. Enterobacter spp. were isolated with increasing frequency from pneumonia and were the most common Gram-negative isolates from bloodstream infections. Device-associated infection rates for bloodstream infections, pneumonia, and urinary tract infections did not correlate with length of stay, the number of hospital beds, or season.

CONCLUSIONS

In pediatric ICUs, bloodstream infections were the most common nosocomial infection. The distribution of infection sites and pathogens differed with age and from that reported from adult ICUs. Device-associated infection rates were the best rates currently available for comparisons between units, because they were not associated with length of stay, the number of beds in the hospital, or season.

Comparison of agar dilution, disk diffusion, MicroScan, and Vitek antimicrobial susceptibility testing methods to broth microdilution for detection of fluoroquinolone-resistant isolates of the family Enterobacteriaceae

Fluoroquinolone resistance appears to be increasing in many species of bacteria, particularly in those causing nosocomial infections. However, the accuracy of some antimicrobial susceptibility testing methods for detecting fluoroquinolone resistance remains uncertain. Therefore, we compared the accuracy of the results of agar dilution, disk diffusion, MicroScan Walk Away Neg Combo 15 conventional panels, and Vitek GNS-F7 cards to the accuracy of the results of the broth microdilution reference method for detection of ciprofloxacin and ofloxacin resistance in 195 clinical isolates of the family Enterobacteriaceae collected from six U.S. hospitals for a national surveillance project (Project ICARE [Intensive Care Antimicrobial Resistance Epidemiology]). For ciprofloxacin, very major error rates were 0% (disk diffusion and MicroScan), 0.9% (agar dilution), and 2.7% (Vitek), while major error rates ranged from 0% (agar dilution) to 3.7% (MicroScan and Vitek). Minor error rates ranged from 12.3% (agar dilution) to 20.5% (MicroScan). For ofloxacin, no very major errors were observed, and major errors were noted only with MicroScan (3.7% major error rate). Minor error rates ranged from 8.2% (agar dilution) to 18.5% (Vitek). Minor errors for all methods were substantially reduced when results with MICs within +/-1 dilution of the broth microdilution reference MIC were excluded from analysis. However, the high number of minor errors by all test systems remains a concern.

Nosocomial infections in coronary care units in the United States. National Nosocomial Infections Surveillance System

To describe the epidemiology of nosocomial infections in Coronary Care Units (CCUs) in the United States, we analyzed data collected between 1992 and 1997 using the standard protocols of the National Nosocomial Infections Surveillance (NNIS) Intensive Care Unit (ICU) surveillance component. Data on 227,451 patients with 6,698 nosocomial infections were analyzed. Urinary tract infections (35%), pneumonia (24%), and primary bloodstream infections (17%) were almost always associated with use of an invasive device (93% with a urinary catheter, 82% with a ventilator, 82% with a central line, respectively). The distribution of pathogens differed from that reported from other types of ICUs. Staphylococcus aureus (21%) was the most common species reported from pneumonia and Escherichia coli (27%) from urine. Only 10% of reported urine isolates were Candida albicans. S. aureus (24%) was the more common bloodstream isolate than enterococci (10%). The mean overall patient infection rate was 2.7 infections per 100 patients. Device-associated infection rates for bloodstream infections, pneumonia, and urinary tract infections did not correlate with length of stay, number of hospital beds, number of CCU beds, or the hospital teaching affiliation, and were the best rates for comparisons between units. Use of invasive devices was lower than in other types of ICUs. Overall patient infection rates were lower than in other types of ICUs, which is largely explained by lower rates of invasive device usage.

Antimicrobial use and resistance in eight US hospitals: complexities of analysis and modeling. Intensive Care Antimicrobial Resistance Epidemiology Project and National Nosocomial Infections Surveillance System Hospitals

OBJECTIVE

To evaluate the relation between antimicrobial use and resistance in intensive-care unit (ICU) and non-ICU inpatient areas in eight US hospitals.

METHODS

We determined antimicrobial use in terms of defined daily doses, antimicrobial-use density (defined daily doses/1,000 patient days), and percentage resistance for five antimicrobial-organism combinations in the ICU and non-ICU inpatient areas of eight US hospitals participating in project Intensive Care Antimicrobial Resistance Epidemiology.

RESULTS

Antimicrobial resistance and use varied tremendously among the eight hospitals. Antimicrobial resistance among these five nosocomial pathogens was significantly higher within the inpatient setting of these hospitals, compared with the outpatient setting. One hospital consistently ranked highest for use of all classes of antimicrobials examined. High antimicrobial use was not associated necessarily with high resistance for a particular antimicrobial-organism pair.

CONCLUSION

Antimicrobial use varied significantly across these hospitals, but generally was higher in ICUs. These results suggest that concomitant surveillance of both antimicrobial resistance and antimicrobial use is helpful in interpreting antimicrobial resistance in a hospital or ICU and that further analysis is required to determine the role of variables other than antimicrobial use in a statistical model for predicting antimicrobial resistance.

Accuracy of reporting nosocomial infections in intensive-care-unit patients to the National Nosocomial Infections Surveillance System: a pilot study

OBJECTIVE

To assess the accuracy of nosocomial infections data reported on patients in the intensive-care unit by nine hospitals participating in the National Nosocomial Infections Surveillance (NNIS) System.

DESIGN

A pilot study was done in two phases to review the charts of selected intensive-care-unit patients who had nosocomial infections reported to the NNIS System. The charts of selected high- and low-risk patients in the same cohort who had no infections reported to the NNIS System also were included. In phase I, trained data collectors reviewed a sample of charts for nosocomial infections. Retrospectively detected infections that matched with previously reported infections were deemed to be true infections. In phase II, two Centers for Disease Control and Prevention (CDC) epidemiologists reexamined a sample of charts for which a discrepancy existed. Each sampled infection either was confirmed or disallowed by the epidemiologists. Confirmed infections also were deemed to be true infections. True infections from both phases were used to estimate the accuracy of reported NNIS data by calculating the predictive value positive, sensitivity, and specificity at each major infection site and the "other sites."

RESULTS

The data collectors examined a total of 1,136 patients' charts in phase I. Among these charts were 611 infections that the study hospitals had reported to the CDC. The data collectors retrospectively matched 474 (78%) of the prospectively identified infections, but also detected 790 infections that were not reported prospectively. Phase II focused on the discrepant infections: the 137 infections that were identified prospectively and reported but not detected retrospectively, and the 790 infections that were detected retrospectively but not reported previously. The CDC epidemiologists examined a sample of 113 of the discrepant reported infections and 369 of the discrepant detected infections, and estimated that 37% of all discrepant reported infections and 43% of all discrepant detected infections were true infections. The predictive value positive for reported bloodstream infections, pneumonia, surgical-site infection, urinary tract infection, and other sites was 87%, 89%, 72%, 92%, and 80%, respectively; the sensitivity was 85%, 68%, 67%, 59%, and 30%, respectively; and the specificity was 98.3%, 97.8%, 97.7%, 98.7%, and 98.6%, respectively.

CONCLUSIONS

When the NNIS hospitals in the study reported a nosocomial infection, the infection most likely was a true infection, and they infrequently reported conditions that were not infections. The hospitals also identified and reported most of the nosocomial infections that occurred in the patients they monitored, but accuracy varied by infection site. Primary bloodstream infection was the most accurately identified and reported site. Measures that will be taken to improve the quality of the infection data reported to the NNIS System include reviewing the criteria for definitions of infections and other data fields, enhancing communication between the CDC and NNIS hospitals, and improving the training of surveillance personnel in NNIS hospitals.

Comparing nosocomial infection rates among surgical intensive-care units: the importance of separating cardiothoracic and general surgery intensive-care units

Among surgical intensive-care units (ICUs), we assessed differences in risk-adjusted nosocomial infection rates between cardiothoracic (CT) and general surgery ICUs, using National Nosocomial Infection Surveillance data from 1987 to 1995. Device-associated rates and average length of stay were significantly lower in CT ICUs. Comparisons of risk-adjusted nosocomial infection rates among CT ICUs should be made separately from rates from general surgery ICUs.

Evidence of interhospital transmission of extended-spectrum beta-lactam-resistant Klebsiella pneumoniae in the United States, 1986 to 1993. The National Nosocomial Infections Surveillance System

BACKGROUND

In addition to single-hospital outbreaks, interhospital transmission of extended-spectrum beta-lactam-resistant (ESBLR) Klebsiella pneumoniae has been suspected in some reports. However, these studies lacked sufficient epidemiological information to confirm such an occurrence.

METHODS

We reviewed the surveillance data reported to the National Nosocomial Infections Surveillance (NNIS) System during 1986 to 1993 for K pneumoniae isolates and their susceptibility to either ceftazidime, cefotaxime, ceftriaxone, or aztreonam. Pulsed-field gel electrophoresis (PFGE) was used to study available ESBLR K pneumoniae isolates.

RESULTS

Among 8,319 K pneumoniae isolates associated with nosocomial infections, 727 (8.7%) were resistant or had intermediate-level resistance to at least one of these antibiotics. One hospital (hospital A) accounted for 321 isolates (44.2%) of ESBLR K pneumoniae. During 1986 to 1993, the percentage of K pneumoniae isolates that were ESBLR increased from 0 to 57.7% in hospital A, from 0 to 35.6% in NNIS hospitals 0 to 20 miles from hospital A (area B), and from 1.6 to 7.3% in NNIS hospitals more than 20 miles from hospital A, including hospitals located throughout the United States. Analysis of PFGE restriction profiles showed a genetic relationship between a cluster of isolates from hospital A and some isolates from one hospital in area B, and consecutive admission in these two hospitals was confirmed for two patients from whom isolates were available.

CONCLUSIONS

These data provide evidence of interhospital transmission of ESBLR K pneumoniae in one region of the United States and stress the interrelationship between hospitals when trying to control antimicrobial resistance.