Surgical wound infection as a performance indicator: agreement of common definitions of wound infection in 4773 patients
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《英国医生杂志》
1 Department of Clinical Microbiology, University College London Hospitals, London WC1E 6DB, 2 Department of Epidemiology and Population Health, London School of Hygiene and Tropical Medicine, London, 3 Department of Medical Physics, University College London Hospitals, 4 Department of Surgery, Medical School, Aberdeen, 5 Department of Public Health, Medical School, Aberdeen, 6 Nosocomial Infection Surveillance Unit, HPA Central Public Health Laboratory, London, 7 Health VFM Audit, National Audit Office, London
Correspondence to: A P R Wilson peter.wilson@uclh.nhs.uk
Abstract
Surgical site infections represent a substantial burden of disease for patients and health services. Patients with such infections experience substantial morbidity, pain and discomfort, inconvenience, and cost and, occasionally, may die. From the perspective of health services, patients with surgical site infections stay in hospital on average about twice as long as uninfected patients, and the cost of total care is more than doubled—inpatient costs of surgical site infections alone were estimated to be about ￡65m in England in 1995.1
The UK government is changing the way postoperative infections are monitored in the NHS. Surveillance of surgical site infection, still commonly referred to as wound infection, became mandatory for orthopaedics in April 2004, and this will soon spread to other specialties.2 The feedback of infection data to surgeons clearly reduces infection rates.3 4 Given that the percentage of wounds classified as infected will probably be used as a performance indicator,5 it is vital that the new surveillance system allows reliable comparisons across NHS institutions, and with overseas health institutions.
Although the UK Department of Health has consulted with experts, it has given little guidance on the definition of surgical site infection that is to be used for surveillance in England, namely the nosocomial infection national surveillance scheme (NINSS) version of the definition set out by the Centers for Disease Control (CDC) in 1992.6 There has been little or no critical evaluation of either the original or modified definition. Moreover, the version or interpretation of the definition used varies between hospitals and regions.7 8 Choosing an appropriate definition and ensuring that the definition is applied consistently are necessary conditions for observed rates of wound infection across hospitals to be valid.
Designers of a national surveillance system must judge the available definitions by their ability to identify infections that matter most to patients and to health services. The practicability of collecting the required information must also be considered, since laborious or complex definitions are less likely to be implemented consistently across hospitals.
We therefore compared agreement between four common definitions of surgical site infection—namely (a) the CDC 1992 definition, (b) the NINSS modification of the CDC definition, (c) the presence of pus, and (d) the ASEPSIS scoring method9—applied to the same series of surgical wounds. We also compared the percentage of infection based on the CDC definition and on the NINSS modification to investigate the potential effect of subjective CDC criteria and of variation between hospitals in data collection methods.
Participants and methods
A total of 5804 surgical wounds in 4773 patients were assessed during 5028 separate hospital admissions to all surgical specialties in the hospital group between May 2000 and July 2003 (table 1). The patients' median age was 53.5 years (interquartile range 37.5-69.6), and 2281 (48%) of the patients were female. The median hospital stay was 8 days (6-14), and duration of operation 111 minutes (62-180).
Table 1 Characteristics of 4773 hospital inpatients who underwent surgery. Values are numbers (percentages) of patients unless stated otherwise
The mean percentage of wound infection differed substantially with the different definitions; 19.2% (95% confidence interval 18.1% to 20.4%) with the CDC definition, 14.6% (13.6% to 15.6%) with the NINSS version, 12.3% (11.4% to 13.2%) with pus alone, and 6.8% (6.1% to 7.5%) with an ASEPSIS score > 20. Table 2 shows the level of agreement between the ASEPSIS and CDC systems. When superficial infections (according to CDC category) were included, 13% (778) of all observed wounds received conflicting diagnoses, and 6% were classified as infected by both definitions. When superficial infections were excluded, the two definitions estimated about the same overall percentage infection (6.8% and 7.0% respectively), but there were almost twice as many conflicting infection diagnoses (n=371) as concordant ones (n=215).
Table 2 Comparison of crude rates of surgical site infection reported with Centers for Disease Control (CDC) 1992 definition and with ASEPSIS scoring method. Wounds were considered to be infected if they met the CDC criteria for either superficial or deep infection (top half of table) or if they met the criteria for deep infection only (bottom half of table). Values are numbers (percentages) of wounds, with 95% confidence intervals for percentages, adjusted for multiple wounds in the same patients
Wounds with pus were automatically diagnosed as infected by the CDC, NINSS, and pus alone definitions, but only 39% of these (283/714) had ASEPSIS scores > 20 (fig 1). For these wounds, the CDC scale also consistently diagnosed greater infection severity than did ASEPSIS. Most wounds with pus were classified by ASEPSIS as having a "disturbance of healing" (39%, 280/714) or as healing satisfactorily (21%, 151/714). Of these latter 151 wounds, 26% were classified as deep infections by the CDC definition.
Fig 1 Comparison of diagnoses of surgical site infection in 5804 wounds reported with Centers for Disease Control (CDC) 1992 definition and with ASEPSIS scoring method, for wounds with and without pus
In wounds without pus the relation of ASEPSIS and CDC scales was less consistent (fig 1). For example, 42% (177/421) of wounds classified only as "disturbance of healing" by ASEPSIS were classified as infected by the CDC definition, with 3.8% (16) classified as deep infections. Conversely, four of the six wounds classified as "severe wound infections" by ASEPSIS were classified as superficial by the CDC definition.
Figure 2 compares the wound classification with the CDC definition and with the NINSS version. Each category of infection showed unique discrepancies between the two definitions. For example, more than 30% of wounds defined as superficially infected with CDC were classified as not infected with NINSS (229/709). In the CDC "superficial infection" category 94% (222/237) of the observed discrepancy was attributable to the NINSS modification of the CDC criterion related to positive bacterial cultures. In the CDC "deep infection" category the discrepancy observed was due to the exclusion of infections based solely on a surgeon's diagnosis.
Fig 2 Comparison of diagnoses of surgical site infection in 5804 wounds reported with the Centers for Disease Control (CDC) 1992 definition and with the nosocomial infection national surveillance scheme (NINSS) version of the CDC definition
Discussion
Plowman R, Graves N, Griffin M, Roberts JA, Swan AV, Cookson B, et al. The socio-economic burden of hospital acquired infection. London: Public Health Laboratory Service, 1999.
Donaldson L, Mullally S. Surveillance of healthcare associated infections. PLCMO2003/4, PLCNO2003/4. London: Department of Health, 2003.
Gil-Egea MJ, Pi-Sunyer MT, Verdaguer A, Sanz F, Sitges-Serra A, Eleizegui LT. Surgical wound infections: prospective study of 4,468 clean wounds. Infect Control 1987;8: 277-80.
Mead PB, Pories SE, Hall P, Vacek PM, Davis JH Jr, Gamelli RL. Decreasing the incidence of surgical wound infections. Validation of a surveillance-notification program. Arch Surg 1986;121: 458-61.
Department of Health. Indicator 23003. In: NHS performance indicators: a consultation. London: DoH, 2001: Annex 1, p 57.
Horan TC, Gaynes RP, Martone WJ, Jarvis WR, Emori TG. CDC definitions of nosocomial surgical site infections, 1992: a modification of CDC definitions of surgical wound infections. Infect Control Hosp Epidemiol 1992;13: 606-8.
Wilson JA, Ward VP, Coello R, Charlett A, Pearson A. A user evaluation of the nosocomial infection national surveillance system: surgical site infection module. J Hosp Infect 2002;52: 114-21.
Bruce J, Russell EM, Mollison J, Krukowski ZH. The measurement and monitoring of surgical adverse events. Health Technol Assess 2001;5(22): 1-194.
Wilson AP, Treasure T, Sturridge MF, Gruneberg RN. A scoring method (ASEPSIS) for postoperative wound infections for use in clinical trials of antibiotic prophylaxis. Lancet 1986;i: 311-3.
Cruse PJ, Foord R. The epidemiology of wound infection. A 10-year prospective study of 62,939 wounds. Surg Clin North Am 1980;60: 27-40.
Armitage P, Berry G, Matthews JNS. Statistical methods in medical research. 4th ed. Oxford: Blackwell, 2001: 703.
Wilson AP, Helder N, Theminimulle SK, Scott GM. Comparison of wound scoring methods for use in audit. J Hosp Infect 1998;39: 119-26.
Colson M, Bolsin S. The use of statistical process control methods in monitoring clinical performance. Int J Qual Health Care 2003;15: 445.
Beaujean D, Veltkamp S, Blok H, Gigengack-Baars A, van der Werken C, Verhoef J, et al. Comparison of two surveillance methods for detecting nosocomial infections in surgical patients. Eur J Clin Microbiol Infect Dis 2002;21: 444-8.
Smith BH, Penny KI, Purves AM, Munro C, Wilson B, Grimshaw J, et al. The chronic pain grade questionnaire: validation and reliability in postal research. Pain 1997;71: 141-7.
Byrne DJ, Malek MM, Davey PG, Cuschieri A. Postoperative wound scoring. Biomed Pharmacother 1989;43: 669-73.
Wilson AP, Webster A, Gruneberg RN, Treasure T, Sturridge MF. Repeatability of asepsis wound scoring method. Lancet 1986;i: 1208-9.
Gaynes R, Richards C, Edwards J, Emori TG, Horan T, Alonso-Echanove J, et al. Feeding back surveillance data to prevent hospital-acquired infections. Emerg Infect Dis 2001;7: 295-8.
Lilford R, Mohammed MA, Spiegelhalter D, Thomson R. Use and misuse of process and outcome data in managing performance of acute medical care: avoiding institutional stigma. Lancet 2004;363: 1147-54.(A P R Wilson, consultant )
Correspondence to: A P R Wilson peter.wilson@uclh.nhs.uk
Abstract
Surgical site infections represent a substantial burden of disease for patients and health services. Patients with such infections experience substantial morbidity, pain and discomfort, inconvenience, and cost and, occasionally, may die. From the perspective of health services, patients with surgical site infections stay in hospital on average about twice as long as uninfected patients, and the cost of total care is more than doubled—inpatient costs of surgical site infections alone were estimated to be about ￡65m in England in 1995.1
The UK government is changing the way postoperative infections are monitored in the NHS. Surveillance of surgical site infection, still commonly referred to as wound infection, became mandatory for orthopaedics in April 2004, and this will soon spread to other specialties.2 The feedback of infection data to surgeons clearly reduces infection rates.3 4 Given that the percentage of wounds classified as infected will probably be used as a performance indicator,5 it is vital that the new surveillance system allows reliable comparisons across NHS institutions, and with overseas health institutions.
Although the UK Department of Health has consulted with experts, it has given little guidance on the definition of surgical site infection that is to be used for surveillance in England, namely the nosocomial infection national surveillance scheme (NINSS) version of the definition set out by the Centers for Disease Control (CDC) in 1992.6 There has been little or no critical evaluation of either the original or modified definition. Moreover, the version or interpretation of the definition used varies between hospitals and regions.7 8 Choosing an appropriate definition and ensuring that the definition is applied consistently are necessary conditions for observed rates of wound infection across hospitals to be valid.
Designers of a national surveillance system must judge the available definitions by their ability to identify infections that matter most to patients and to health services. The practicability of collecting the required information must also be considered, since laborious or complex definitions are less likely to be implemented consistently across hospitals.
We therefore compared agreement between four common definitions of surgical site infection—namely (a) the CDC 1992 definition, (b) the NINSS modification of the CDC definition, (c) the presence of pus, and (d) the ASEPSIS scoring method9—applied to the same series of surgical wounds. We also compared the percentage of infection based on the CDC definition and on the NINSS modification to investigate the potential effect of subjective CDC criteria and of variation between hospitals in data collection methods.
Participants and methods
A total of 5804 surgical wounds in 4773 patients were assessed during 5028 separate hospital admissions to all surgical specialties in the hospital group between May 2000 and July 2003 (table 1). The patients' median age was 53.5 years (interquartile range 37.5-69.6), and 2281 (48%) of the patients were female. The median hospital stay was 8 days (6-14), and duration of operation 111 minutes (62-180).
Table 1 Characteristics of 4773 hospital inpatients who underwent surgery. Values are numbers (percentages) of patients unless stated otherwise
The mean percentage of wound infection differed substantially with the different definitions; 19.2% (95% confidence interval 18.1% to 20.4%) with the CDC definition, 14.6% (13.6% to 15.6%) with the NINSS version, 12.3% (11.4% to 13.2%) with pus alone, and 6.8% (6.1% to 7.5%) with an ASEPSIS score > 20. Table 2 shows the level of agreement between the ASEPSIS and CDC systems. When superficial infections (according to CDC category) were included, 13% (778) of all observed wounds received conflicting diagnoses, and 6% were classified as infected by both definitions. When superficial infections were excluded, the two definitions estimated about the same overall percentage infection (6.8% and 7.0% respectively), but there were almost twice as many conflicting infection diagnoses (n=371) as concordant ones (n=215).
Table 2 Comparison of crude rates of surgical site infection reported with Centers for Disease Control (CDC) 1992 definition and with ASEPSIS scoring method. Wounds were considered to be infected if they met the CDC criteria for either superficial or deep infection (top half of table) or if they met the criteria for deep infection only (bottom half of table). Values are numbers (percentages) of wounds, with 95% confidence intervals for percentages, adjusted for multiple wounds in the same patients
Wounds with pus were automatically diagnosed as infected by the CDC, NINSS, and pus alone definitions, but only 39% of these (283/714) had ASEPSIS scores > 20 (fig 1). For these wounds, the CDC scale also consistently diagnosed greater infection severity than did ASEPSIS. Most wounds with pus were classified by ASEPSIS as having a "disturbance of healing" (39%, 280/714) or as healing satisfactorily (21%, 151/714). Of these latter 151 wounds, 26% were classified as deep infections by the CDC definition.
Fig 1 Comparison of diagnoses of surgical site infection in 5804 wounds reported with Centers for Disease Control (CDC) 1992 definition and with ASEPSIS scoring method, for wounds with and without pus
In wounds without pus the relation of ASEPSIS and CDC scales was less consistent (fig 1). For example, 42% (177/421) of wounds classified only as "disturbance of healing" by ASEPSIS were classified as infected by the CDC definition, with 3.8% (16) classified as deep infections. Conversely, four of the six wounds classified as "severe wound infections" by ASEPSIS were classified as superficial by the CDC definition.
Figure 2 compares the wound classification with the CDC definition and with the NINSS version. Each category of infection showed unique discrepancies between the two definitions. For example, more than 30% of wounds defined as superficially infected with CDC were classified as not infected with NINSS (229/709). In the CDC "superficial infection" category 94% (222/237) of the observed discrepancy was attributable to the NINSS modification of the CDC criterion related to positive bacterial cultures. In the CDC "deep infection" category the discrepancy observed was due to the exclusion of infections based solely on a surgeon's diagnosis.
Fig 2 Comparison of diagnoses of surgical site infection in 5804 wounds reported with the Centers for Disease Control (CDC) 1992 definition and with the nosocomial infection national surveillance scheme (NINSS) version of the CDC definition
Discussion
Plowman R, Graves N, Griffin M, Roberts JA, Swan AV, Cookson B, et al. The socio-economic burden of hospital acquired infection. London: Public Health Laboratory Service, 1999.
Donaldson L, Mullally S. Surveillance of healthcare associated infections. PLCMO2003/4, PLCNO2003/4. London: Department of Health, 2003.
Gil-Egea MJ, Pi-Sunyer MT, Verdaguer A, Sanz F, Sitges-Serra A, Eleizegui LT. Surgical wound infections: prospective study of 4,468 clean wounds. Infect Control 1987;8: 277-80.
Mead PB, Pories SE, Hall P, Vacek PM, Davis JH Jr, Gamelli RL. Decreasing the incidence of surgical wound infections. Validation of a surveillance-notification program. Arch Surg 1986;121: 458-61.
Department of Health. Indicator 23003. In: NHS performance indicators: a consultation. London: DoH, 2001: Annex 1, p 57.
Horan TC, Gaynes RP, Martone WJ, Jarvis WR, Emori TG. CDC definitions of nosocomial surgical site infections, 1992: a modification of CDC definitions of surgical wound infections. Infect Control Hosp Epidemiol 1992;13: 606-8.
Wilson JA, Ward VP, Coello R, Charlett A, Pearson A. A user evaluation of the nosocomial infection national surveillance system: surgical site infection module. J Hosp Infect 2002;52: 114-21.
Bruce J, Russell EM, Mollison J, Krukowski ZH. The measurement and monitoring of surgical adverse events. Health Technol Assess 2001;5(22): 1-194.
Wilson AP, Treasure T, Sturridge MF, Gruneberg RN. A scoring method (ASEPSIS) for postoperative wound infections for use in clinical trials of antibiotic prophylaxis. Lancet 1986;i: 311-3.
Cruse PJ, Foord R. The epidemiology of wound infection. A 10-year prospective study of 62,939 wounds. Surg Clin North Am 1980;60: 27-40.
Armitage P, Berry G, Matthews JNS. Statistical methods in medical research. 4th ed. Oxford: Blackwell, 2001: 703.
Wilson AP, Helder N, Theminimulle SK, Scott GM. Comparison of wound scoring methods for use in audit. J Hosp Infect 1998;39: 119-26.
Colson M, Bolsin S. The use of statistical process control methods in monitoring clinical performance. Int J Qual Health Care 2003;15: 445.
Beaujean D, Veltkamp S, Blok H, Gigengack-Baars A, van der Werken C, Verhoef J, et al. Comparison of two surveillance methods for detecting nosocomial infections in surgical patients. Eur J Clin Microbiol Infect Dis 2002;21: 444-8.
Smith BH, Penny KI, Purves AM, Munro C, Wilson B, Grimshaw J, et al. The chronic pain grade questionnaire: validation and reliability in postal research. Pain 1997;71: 141-7.
Byrne DJ, Malek MM, Davey PG, Cuschieri A. Postoperative wound scoring. Biomed Pharmacother 1989;43: 669-73.
Wilson AP, Webster A, Gruneberg RN, Treasure T, Sturridge MF. Repeatability of asepsis wound scoring method. Lancet 1986;i: 1208-9.
Gaynes R, Richards C, Edwards J, Emori TG, Horan T, Alonso-Echanove J, et al. Feeding back surveillance data to prevent hospital-acquired infections. Emerg Infect Dis 2001;7: 295-8.
Lilford R, Mohammed MA, Spiegelhalter D, Thomson R. Use and misuse of process and outcome data in managing performance of acute medical care: avoiding institutional stigma. Lancet 2004;363: 1147-54.(A P R Wilson, consultant )