Infection Control and Hospital Endhmiology

OBJECTIVES: To report the pooled results of seven prevalence surveys of hospital-acquired infections conducted between November 1996 and November 1999, and to use the data to predict the cumulative incidence of hospital-acquired infections in the same patient group. DESIGN: The summary and modeling of data gathered from the routine surveillance of the point prevalence of hospitalacquired infections. SETTING: Auckland District Health Board Hospitals (Auckland DHBH), the largest publicly funded hospital group in New Zealand supplying secondary and tertiary services. PATIENTS: All inpatients. METHOD: Point-prevalence surveys were conducted including all patients in Auckland DHBH. Standard definitions of hospital-acquired infection were used. The data from the seven surveys were pooled and used in a modeling exercise to predict the cumulative incidence of hospital-acquired infection. An existng method for the conversion of prevalence to cumulative incidence was applied. Results are presented for all patients and stratfied by clinical service and site of hospital-acquired infection. RESULTS: The underlying patterns of hospital-acquired nfection by site and service were stable during the seven time periods. The prevalence rate for all patients was 9.5%, with 553 patients identified with one or more hospital-acquired infections from a population of 5,819. The predicted cumulative incidence for all patients was 6.33% (95% confidence interval, 6.20% to 6.46%). CONCLUSIONS: The prevalence and the predicted cumulative incidence are similar to rates reported in the international literature. The validity of the predicted cumulative incidence derived here is not known. If it were accurate, then the application of this method would represent a cost-effective alternative to incidence studies (Infect Control Hosp Epidemiol 2003;24:56-61). Hospital-acquired infection imposes costs on hospitals, community care services, and patients and their families. When patients and their families are delayed in their return to productive activities, losses in productivity also accrue. Hospital-acquired infection also has an impact on the mortality rate. Data from the United States suggest that 10% of patients with a hospital-acquired infection die in the hospital. The hospital-acquired infection is the main cause in 10% of these deaths and a contributory factor in another 30%. It has been argued that the economic benefits of prevention are likely to exceed the costs." Data on the costs of hospital-acquired infection and the cost-effectiveness of prevention programs should be made available to policymakers. However, before these data can be procured, it is necessary to understand the size and the extent of the problem. Point-prevalence surveys have been conducted twice a year, in May and November, since 1996 in Auckland District Health Board Hospitals. The results of the first survey have been published and showed that 12% of patients had a hospital-acquired infection on the day of the survey. Because hospital-acquired infection prolongs the hospital stay, the likelihood of such patients' being sampled in a prevalence survey increases; thus, the prevalence rate may not provide a true picture of the pattern of disease over time. A more useful measure of hospital-acquired infection is the cumulative incidence, because this illustrates the number of patients who acquire a hospital-acquired infection during a defined time period (eg, a year) and the number of cases may be expressed as a percentage of total discharges. Incidence studies are expensive to conduct, because data have to be collected on every new admission for a defined period. Auckland District Health Board Hospitals is New Zealand's largest publicly funded, tertiary healthcare provider, with four specialist teaching hospitals treating a total of 95,999 inpatients annually. Three of the four hospitals are included in this study. Auckland Hospital has 560 Dr. Graves is from the Centre for Health Care Related Infection Surveillance and Prevention, Princess Alexandra Hospital, and the School of Public Health, Queensland University of Technology, Queensland, Australia. Ms. Nicholls is from the Auckland District Health Board, Auckland, New Zealand. Mr. Wong is from the Middlemore Hospital Auckland, Auckland, New Zealand. Dr. Morris is from the Auckland District Health Board, Infection Control Service, Auckland, New Zealand. Address reprint requests to Dr. Nicholas Graves, School of Public Health, QUT, Victoria Park Road, Kelvin Grove, QLD, 4059, Australia. The authors thank infectious disease physicians and registrars, clinical microbiologists and registrars, and the infection control nurse practitioners for the Auckland District Health Board Hospitals for data collection; Josephine Power for data entry; and Jenny Connor, Elizabeth Robinson, and Roger Marshall, Department of Community Health, University of Auckland, for advice on hospital epidemiology and statistical analysis. https://www.cambridge.org/core/terms. https://doi.org/10.1086/502116 Downloaded from https://www.cambridge.org/core. IP address: 54.191.40.80, on 14 Jul 2017 at 05:37:14, subject to the Cambridge Core terms of use, available at Vol. 24 No. 1 HOSPITAL-ACQUIRED INFECTIONS IN N E W ZEALAND 57 beds and provides emergency, acute, and elective general medical and surgical services, as well as major hematology, oncology, and liver transplant services. Green Lane Hospital has 197 beds and provides otorhinolaryngology, cardiology, respiratory medicine, and cardiothoracic surgery services, including heart and lung transplants. National Women's Hospital has 180 beds, delivers approximately 7,500 infants per year, and provides neonatal intensive care and gynecologic services. The fourth hospital was a specialist pediatrics hospital whose patients were not included in any of the prevalence surveys. This article reports the results of seven prevalence studies conducted between November 1996 and November 1999, and derives an estimate of the cumulative incidence of hospital-acquired infection from these prevalence data. The method used was previously applied in two studies and found to produce valid results. METHODS Prevalence Survey The methods used for the prevalence surveys have been reported in detail elsewhere. In summary, all inpatients at the three sites of Auckland District Health Board Hospitals were included. Data collection was by twoperson teams possibly including a clinical microbiologist, an infectious diseases physician, and an infection control nurse. The clinical records of each patient were examined, and, if required, additional data were collected from the team caring for the patient. The following demographic and clinical data were recorded on a standardized data collection form: age, gender, admission date, hospital, ward, clinical service, duration of stay, presence of infection on admission, whether infection was related to a previous admission, infection present or under treatment on day of survey, site of infection, and causative organism. In addition, data were recorded on extrinsic risk factors. The definitions of the Centers for Disease Control and Prevention were used to identify the presence of hospital-acquired infection. The numbers of hospital-acquired infections observed on the day of the survey, which related to that admission, were divided by the number of inpatients on that day to derive a measure of the prevalence. Conversion of Prevalence Data to Estimates of Cumulative Incidence The formula