Shailen N. Banerjee

National nosocomial infections surveillance system (NNIS): Description of surveillance methods

The National Nosocomial Infections Surveillance System (NNIS) is an ongoing collaborative surveillance system sponsored by the Centers for Disease Control (CDC) to obtain national data on nosocomial infections. The CDC uses the data that are reported voluntarily by participating hospitals to estimate the magnitude of the nosocomial infection problem in the United States and to monitor trends in infections and risk factors. Hospitals collect data by prospectively monitoring specific groups of patients for infections with the use of protocols called surveillance components. The surveillance components used by the NNIS are hospitalwide, intensive care unit, high-risk nursery, and surgical patient. Detailed information including demographic characteristics, infections and related risk factors, pathogens and their antimicrobial susceptibilities, and outcome, is collected on each infected patient. Data on risk factors in the population of patients being monitored are also collected; these permit the calculation of risk-specific rates. An infection risk index, which includes the traditional wound class, is being evaluated as a predictor of the likelihood that an infection will develop after an operation. A major goal of the NNIS is to use surveillance data to develop and evaluate strategies to prevent and control nosocomial infections. The data collected with the use of the surveillance components permit the calculation of risk-specific infection rates, which can be used by individual hospitals as well as national health-care planners to set priorities for their infection control programs and to evaluate the effectiveness of their efforts. The NNIS will continue to evolve in finding more effective and efficient ways to assess the influence of patient risk and changes in the financing of health care on the infection rate.

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.

Transfusion‐transmitted bacterial infectionin the United States, 1998 through 2000

BACKGROUND: Bacterial contamination of blood components can result in transfusion‐transmitted infection, but the risk is not established.

Secular Trends in Hospital-Acquired Clostridium difficile Disease in the United States, 1987–2001

We reviewed Clostridium difficile-associated disease (CDAD) data from the intensive care unit (ICU) and hospital-wide surveillance components of the National Nosocomial Infections Surveillance System hospitals during 1987-2001. ICU CDAD rates increased significantly only in hospitals with >500 beds (P<.01) and correlated with the duration of ICU stay (r=0.82; P<.05). Hospital-wide (non-ICU) rates increased only in hospitals with <250 beds (P<.01) and in general medicine patients versus surgery patients (P<.0001). CDAD predominated in general hospitals versus other facility types, and rates were significantly higher during winter versus nonwinter months (P<.01). Thus, prevention efforts should be targeted to high-risk groups in these settings.

Patient density, nurse-to-patient ratio and nosocomial infection risk in a pediatric cardiac intensive care unit.

BACKGROUND An investigation of a Serratia marcescens outbreak in a pediatric cardiac intensive care unit (CICU) suggested that understaffing or overcrowding might have been underlying risk factors. OBJECTIVE To assess the effect of fluctuations in CICU nurse staffing levels and patient census on CICU nosocomial infection rate (NIR). METHODS The monthly CICU nursing hours, patient days and nosocomial infections were obtained from retrospective review of administrative, patient and microbiology records during December, 1994, through December, 1995 (study period). The NIR and nursing hours:patient day ratio were then calculated. The correlations between NIR vs. nursing hours, patient days and nursing hours:patient day ratio were determined. RESULTS The median monthly CICU NIR was 6.9 (range, 0 to 15.2) infections per 1000 patient days; the median number of hours worked per month by CICU registered nurses was 7754 (range, 7133 to 8452) hours; the median number of patient days treated per month was 507 (range, 381 to 590) patient days; and the median monthly nursing hours:patient day ratio was 15.2:1 (range, 13.2:1 to 19.9:1). The strongest linear correlation was observed between the monthly NIR and patient days (r = 0.89, P = 0.0001). There was an inverse correlation between the monthly NIR and nursing hours:patient day ratio (r = -0.77, P = 0.003). CONCLUSIONS The NIR was most strongly correlated with patient census but also was strongly associated with the nursing hours:patient day ratio. These factors may influence the infection rate because of breaks in health care worker aseptic technique or decreased hand washing. Increased patient census alone may increase the risk of cross-transmission of nosocomial infections. As hospitals proceed with cost containment efforts the effect of fluctuations in patient census and nurse staffing on patient outcomes needs evaluation.

Swab Materials and Bacillus anthracis Spore Recovery from Nonporous Surfaces

Four swab materials were evaluated for their efficiency in recovery of Bacillus anthracis spores from steel coupons. Cotton, macrofoam, polyester, and rayon swabs were used to sample coupons inoculated with a spore suspension of known concentration. Three methods of processing for the removal of spores from the swabs (vortexing, sonication, or minimal agitation) and two swab preparations (premoistened and dry) were evaluated. Results indicated that premoistened swabs were more efficient at recovering spores than dry swabs (14.3% vs. 4.4%). Vortexing swabs for 2 min during processing resulted in superior extraction of spores when compared to sonicating them for 12 min or subjecting them to minimal agitation. Premoistened macrofoam and cotton swabs that were vortexed during processing recovered the greatest proportions of spores with a mean recovery of 43.6% (standard deviation [SD] 11.1%) and 41.7% (SD 14.6%), respectively. Premoistened and vortexed polyester and rayon swabs were less efficient, at 9.9% (SD 3.8%) and 11.5% (SD 7.9%), respectively.

Bloodstream Infection Associated with Needleless Device Use and the Importance of Infection-Control Practices in the Home Health Care Setting

The influence of infection-control practices on bloodstream infection (BSI) risk was examined in a home health care setting in which three needleless devices were used consecutively. A case-control study and a retrospective cohort study were conducted. Risk factors for BSI included lower education level, younger age, having a central venous catheter (CVC) with multiple ports, or having a tunneled CVC. Among patients with a tunneled CVC, those at greatest risk had been allowed to shower rather than bathe and to get their exit site wet (P<.01). A high proportion (49%) of isolates were hydrophilic gram-negative bacteria, suggesting water sources of infection. In the cohort study, the BSI rate decreased as the frequency of changing the needleless device end cap increased from once weekly up to every 2 days, suggesting that the mechanism for BSI may involve contamination from the end cap. These findings may help to develop infection-control measures specific to home health care.

Serratia marcescens outbreak associated with extrinsic contamination of 1% chlorxylenol soap.

OBJECTIVES To determine risk factors for Serratia marcescens infection or colonization, and to identify the source of the pathogen and factors facilitating its persistence in a neonatal intensive-care unit (NICU) during an outbreak. DESIGN Retrospective case-control study; review of NICU infection control policies, soap use, and handwashing practices among healthcare workers (HCWs); and selected environmental cultures. SETTING A university-affiliated tertiary-care hospital NICU. PATIENTS All NICU infants with at least one positive culture for S marcescens during August 1994 to October 1995. Infants who did not develop S marcescens infection or colonization were selected randomly as controls. RESULTS Thirty-two patients met the case definition. On multivariate analysis, independent risk factors for S marcescens infection or colonization were having very low birth weight (< 1,500 g), a patent ductus arteriosus, a mother with chorioamnionitis, or exposure to a single HCW. During January to July 1995, NICU HCWs carried their own bottles of 1% chlorxylenol soap, which often were left standing inverted in the NICU sink and work areas. Cultures of 16 (31%) of 52 samples of soap and 1 (8%) of 13 sinks yielded S marcescens. The 16 samples of soap all came from opened 4-oz bottles carried by HCWs. DNA banding patterns of case infant, HCW soap bottle, and sink isolates were identical. CONCLUSIONS Extrinsically contaminated soap contributed to an outbreak of S marcescens infection. Very-low-birth-weight infants with multiple invasive procedures and exposures to certain HCWs were at greatest risk of S marcescens infection or colonization.

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.

Investigation of Postoperative Allograft-Associated Infections in Patients Who Underwent Musculoskeletal Allograft Implantation

BACKGROUND The rate at which allografts are used in surgical procedures has doubled in the United States during the past decade. In 2002, one outpatient surgical center (SC-X) identified a cluster of surgical site infections (SSIs) after anterior cruciate ligament reconstructive surgery (ACLRS). Therefore, we conducted an investigation to determine the extent of the outbreak and to identify risk factors. METHODS Our investigation included retrospective cohort and observational studies. A case patient was defined as any patient who acquired a SSI after undergoing ACLRS at SC-X between February 2000 and June 2002 (the study period). Data collected included demographic characteristics, clinical information, and graft details, such as processing method (i.e., aseptic or sterile). RESULTS Of 331 patients who underwent ACLRS during the study period, 11 (3.3%) met the case definition. All infections occurred at the tibial fixation site of the graft and involved 8 different microorganisms; the median time to a positive culture result was 55 days after ACLRS. The infection rate for patients who received aseptically processed allografts was 4.4% (11 of 250 patients), compared with 0% (0 of 81) for patients who received autografts or sterile allografts (P=.07). Use of a supplementary staple for tibial fixation, compared with other fixation methods that did not involve such staples, increased the risk of infection 10-fold in univariate analysis (relative risk [RR], 10.0; 95% confidence interval [CI], 3.0-32.9) and 9-fold when controlling for tissue processing method (RR, 9.0; 95% CI, 2.8-28.8). CONCLUSIONS The use of sterile allograft tissue appears to be associated with a significant reduction in the risk of postoperative infection, particularly in the presence of adjunctive fixation. Larger clinical studies are necessary to confirm this observation.