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.

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.

Nosocomial infections among neonates in high-risk nurseries in the United States. National Nosocomial Infections Surveillance System.

BACKGROUND: Nosocomial infections result in considerable morbidity and mortality among neonates in high-risk nurseries (HRNs). PURPOSE: To examine the epidemiology of nosocomial infections among neonates in level III HRNs. METHODS: Data were collected from 99 hospitals with HRNs participating in the National Nosocomial Infections Surveillance system, which uses standard surveillance protocols and nosocomial infection site definitions. The data included information on maternal acquisition of and risk factors for infection, such as device exposure, birth weight category (< or = 1000, 1001 through 1500, 1501 through 2500, and > 2500 g), mortality, and the relationship of the nosocomial infection to death. RESULTS: From October 1986 through September 1994, these hospitals submitted data on 13 179 nosocomial infections. The bloodstream was the most frequent site of nosocomial infection in all birth weight groups. Nosocomial pneumonia was the second most common infection site, followed by the gastrointestinal and eye, ear, nose, and throat sites. The most common nosocomial pathogens among all neonates were coagulase-negative staphylococci, Staphylococcus aureus, enterococci, Enterobacter sp, and Escherichia coli. Group B streptococci were associated with 46% of bloodstream infections that were maternally acquired; coagulase-negative staphylococci were associated with 58% of bloodstream infections that were not maternally acquired, most of which (88%) were associated with umbilical or central intravenous catheters. CONCLUSIONS: Bloodstream infections, the most frequent nosocomial infections in all birth weight groups, should be a major focus of surveillance and prevention efforts in HRNs. For bloodstream infections, stratification of surveillance data by maternal acquisition will help focus prevention efforts for group B streptococci outside the HRN. Within the nursery, bloodstream infection surveillance should focus on umbilical or central intravenous catheter use, a major risk factor for infection.

Methicillin-resistant Staphylococcus aureus in U.S. hospitals, 1975-1991.

OBJECTIVES: Analyze changes that have occurred among U.S. hospitals over a 17-year period, 1975 through 1991, in the percentage of Staphylococcus aureus resistant to beta-lactam antibiotics and associated with nosocomial infections. DESIGN: Retrospective review. The percentage of methicillin-resistant S aureus (MRSA) was defined as the number of S aureus isolates resistant to either methicillin, oxacillin, or nafcillin divided by the total number of S aureus isolates for which methicillin, oxacillin, or nafcillin susceptibility test results were reported to the National Nosocomial Infections Surveillance (NNIS) System. SETTING: NNIS System hospitals. RESULTS: Of the 66,132 S aureus isolates that were tested for susceptibility to methicillin, oxacillin, or nafcillin during 1975 through 1991, 6,986 (11%) were resistant to methicillin, oxacillin, or nafcillin. The percentage MRSA among all hospitals rose from 2.4% in 1975 to 29% in 1991, but the rate of increase differed significantly among 3 bed-size categories: < 200 beds, 200 to 499 beds, and > or = 500 beds. In 1991, for hospitals with < 200 beds, 14.9% of S aureus isolates were MRSA; for hospitals with 200 to 499 beds, 20.3% were MRSA; and for hospitals with > or = 500 beds, 38.3% were MRSA. The percentage MRSA in each of the bed-size categories rose above 5% at different times: in 1983, for hospitals with > or = 500 beds; in 1985, for hospitals with 200 to 499 beds; and in 1987, for hospitals with < 200 beds. CONCLUSIONS: This study suggests that hospitals of all sizes are facing the problem of MRSA, the problem appears to be increasing regardless of hospital size, and control measures advocated for MRSA appear to require re-evaluation. Further study of MRSA in hospitals would benefit our understanding of this costly pathogen.

Comparison of rates of nosocomial infections in neonatal intensive care units in the United States. National Nosocomial Infections Surveillance System.

To determine nosocomial infection (NI) rates among neonatal intensive care units (NICUs) that are useful for interhospital comparison, we analyzed data reported in 1986-1990 from 35 hospitals that have level III NICUs and used standard National Nosocomial Infections Surveillance protocols and NI site definitions. Overall rates of NI were calculated as the number of NI per 100 patients (overall NI patient rates) or the number of NI per 1,000 NICU patient-days (overall NI patient-day rates). A strong positive association was found between overall NI patient rates and the neonates' average length of stay, a marker for duration of exposure to important risk factors. No correlation was found between overall NI patient-day rates and average length of stay. However, a strong positive correlation between overall NI patient-day rates and a measure of device utilization (total device-days/total patient-days x 100) was found. Additionally, a positive correlation between overall NI patient rates and device utilization was found. Stratification among the three birthweight groups (less than 1,500 g, 1,500-2,500 g, greater than 2,500 g) did not eliminate the need to control for variations in these factors among NICUs. Device-associated, device-day infection rates, calculated as the number of umbilical or central line-associated blood-stream infections per 1,000 umbilical or central line-days and the number of ventilator-associated pneumonias per 1,000 ventilator days, were not correlated with a unit's site-specific device utilization. These data suggest that calculation of device-associated NI rates in NICUs using device-days as the denominator helps to control for the duration of exposure to the primary risk factor and will be more meaningful for purposes of interhospital comparison.

Nosocomial infections in elderly patients in the United States, 1986-1990. National Nosocomial Infections Surveillance System.

We analyzed 101,479 nosocomial infections in 75,398 adult patients (greater than 15 years) that were reported to the National Nosocomial Infections Surveillance (NNIS) system between 1986 and 1990 by 89 hospitals using the NNIS hospital-wide surveillance component. Overall, 54% of the infections occurred in elderly patients (greater than or equal to 65 years). In the elderly, 44% of the infections were urinary tract infections (UTIs), 18% were pneumonias, 11% were surgical wound infections (SWIs), 8% were bloodstream infections (BSIs), and the remainder were infections at other sites. When we compared the infections in elderly patients with those in younger adult patients, ages 15 to 64 years, a far greater percentage of the infections in elderly patients were UTIs, and there were more pneumonias than SWIs. Elderly and younger patients with ventilator-associated pneumonia were about 1.5 times more likely to develop a secondary BSI than those with pneumonia not associated with ventilator use. When the pathogens isolated from the infections were compared to those reported to the NNIS system in 1984, the percentage that were coagulase-negative staphylococci had increased in both elderly and younger patients. The patient died in 12% of all of the infections. Surveillance personnel reported that 54% of the infections in elderly infected patients who died were related to death compared with 59% in younger infected patients who died. When the infection was related to the patient's death, it was most often pneumonia or a BSI. The risk of an infection-related death was significantly higher when the infected patient developed a secondary BSI. Infection prevention efforts should target infections that occur frequently, are amenable to intervention, and have an adverse outcome.

The National Nosocomial Infections Surveillance System: plans for the 1990s and beyond.

The National Nosocomial Infections Surveillance (NNIS) System is an ongoing collaborative surveillance system among the Centers for Disease Control (CDC) and United States hospitals to obtain national data on nosocomial infections. This system provides comparative data for hospitals and can be used to identify changes in infection sites, risk factors, and pathogens, and develop efficient surveillance methods. Data are collected prospectively using four surveillance components: hospital-wide, intensive care unit, high-risk nursery, and surgical patient. The limitations of NNIS data include the variability in case-finding methods, infrequency or unavailability of culturing, and lack of consistent methods for post-discharge surveillance. Future plans include more routine feedback of data, studies on the validity of NNIS data, new components, a NNIS consultant group, and more rapid data exchange with NNIS hospitals. Increasing the number of NNIS hospitals and cooperating with other agencies to exchange data may allow NNIS data to be used better for generating benchmark nosocomial infection rates. The NNIS system will continue to evolve as it seeks to find more effective and efficient ways to measure the nosocomial infection experience and assess the influence of patient risk, changes in the delivery of hospital care, and changes in infection control practices on these measures.

Surgical wound infection rates by wound class, operative procedure, and patient risk index. National Nosocomial Infections Surveillance System.

To perform a valid comparison of rates among surgeons, among hospitals, or across time, surgical wound infection (SWI) rates must account for the variation in patients' underlying severity of illness and other important risk factors. From January 1987 through December 1990, 44 National Nosocomial Infections Surveillance System hospitals reported data collected under the detailed option of the surgical patient surveillance component protocol, which includes definitions of eligible patients, operations, and nosocomial infections. Pooled mean SWI rates (number of infections per 100 operations) within each of the categories of the traditional wound classification system were 2.1, 3.3, 6.4, and 7.1, respectively. A risk index was developed to predict a surgical patient's risk of acquiring an SWI. The risk index score, ranging from 0 to 3, is the number of risk factors present among the following: (1) a patient with an American Society of Anesthesiologists preoperative assessment score of 3, 4, or 5, (2) an operation classified as contaminated or dirty-infected, and (3) an operation lasting over T hours, where T depends upon the operative procedure being performed. The SWI rates for patients with scores of 0, 1, 2, and 3 were 1.5, 2.9, 6.8, and 13.0, respectively. The risk index is a significantly better predictor of SWI risk than the traditional wound classification system and performs well across a broad range of operative procedures.