Quantifying excess length of postoperative stay attributable to infections: a comparison of methods

Estimating excess length of stay due to healthcare-associated infections: a systematic review and meta-analysis of statistical methodology

BACKGROUND

Healthcare-associated infection (HCAI) affects millions of patients worldwide. HCAI is associated with increased healthcare costs, owing primarily to increased hospital length of stay (LOS) but calculating these costs is complicated due to time-dependent bias. Accurate estimation of excess LOS due to HCAI is essential to ensure that we invest in cost-effective infection prevention and control (IPC) measures.

AIM

To identify and review the main statistical methods that have been employed to estimate differential LOS between patients with, and without, HCAI; to highlight and discuss potential biases of all statistical approaches.

METHODS

A systematic review from 1997 to April 2017 was conducted in PubMed, CINAHL, ProQuest and EconLit databases. Studies were quality-assessed using an adapted Newcastle-Ottawa Scale (NOS). Methods were categorized as time-fixed or time-varying, with the former exhibiting time-dependent bias. Two examples of meta-analysis were used to illustrate how estimates of excess LOS differ between different studies.

FINDINGS

Ninety-two studies with estimates on excess LOS were identified. The majority of articles employed time-fixed methods (75%). Studies using time-varying methods are of higher quality according to NOS. Studies using time-fixed methods overestimate additional LOS attributable to HCAI. Undertaking meta-analysis is challenging due to a variety of study designs and reporting styles. Study differences are further magnified by heterogeneous populations, case definitions, causative organisms, and susceptibilities.

CONCLUSION

Methodologies have evolved over the last 20 years but there is still a significant body of evidence reliant upon time-fixed methods. Robust estimates are required to inform investment in cost-effective IPC interventions.

A Prospective Study of Outcomes, Healthcare Resource Utilization, and Costs Associated With Postoperative Nosocomial Infections

Objective.

We evaluated 4 important outcomes associated with postoperative nosocomial infection: costs, mortality, excess length of stay, and utilization of healthcare resources.

Design.

The outcomes for patients who underwent general, cardiothoracic, and neurosurgical operations were recorded during a previous clinical trial. Multivariable analyses including significant covariates were conducted to determine whether nosocomial infection significantly affected the outcomes.

Setting.

A large tertiary care medical center and an affiliated Veterans Affairs Medical Center.

Patients.

A total of 3,864 surgical patients.

Results.

The overall nosocomial infection rate was 11.3%. Important covariates included age, Karnofsky score, McCabe and Jackson classification of the severity of underlying disease, National Nosocomial Infection Surveillance system risk index, and number of comorbidities. After accounting for covariates, nosocomial infection was associated with increased postoperative length of stay, increased costs, increased hospital readmission rate, and increased use of antimicrobial agents in the outpatient setting. Nosocomial infection was not associated independently with a significantly increased risk of death in this surgical population.

Conclusion.

Postoperative nosocomial infection was associated with increased costs of care and with increased utilization of medical resources. To accurately assess the effects of nosocomial infections, one must take into account important covariates. Surgeons seeking to decrease the cost of care and resource utilization must identify ways to decrease the rate of postoperative nosocomial infection.

Ceftobiprole medocaril is an effective treatment against methicillin-resistant Staphylococcus aureus (MRSA) mediastinitis in a rat model

Methicillin-resistant Staphylococcus aureus (MRSA) mediastinitis after median sternotomy is a major complication of cardiac surgery with significant morbidity and mortality rates. We evaluated the efficacy of ceftobiprole medocaril in a new rat model of mediastinitis and compared it to vancomycin. The model was induced in 92 rats. Infection was induced immediately after median sternotomy by the injection of MRSA (strain 3020, 1 × 10(7) cfu/rat) into the sternal bone. After 24 h, rats (groups of 6-8) were treated intraperitoneally for 5 days or 14 days by either: (i) saline (control, q8h), (ii) ceftobiprole medocaril (70 or 100 mg/kg, q8h), or (iii) vancomycin (50 mg/kg, q12h). Efficacy was determined by a reduction in bacterial cfu in the sternum and spleen tissues. Comparisons were performed using the Mann-Whitney test. A 5-day treatment course of ceftobiprole at both doses tested lead to a significant reduction in MRSA load in the sternum (p < 0.01) as compared to the control group and compared to 5-day vancomycin treatment, which lead to a non-significant reduction (p = 0.07). Longer treatment (14 days) with ceftobiprole lead to a complete clearance of MRSA from the sternum, similarly to vancomycin. Ceftobiprole also showed a significant effect on eliminating MRSA dissemination to the spleen compared to saline-treated rats. Ceftobiprole was effective in treating MRSA mediastinitis in the rat model. In the 5-day course, ceftobiprole showed a significant reduction in sternal MRSA counts and was superior to vancomycin. After 14 days, both ceftobiprole and vancomycin showed clearance of MRSA from the sternum in more than 50 % of rats and almost complete clearance in the remainder.

Cost effectiveness of local collagen-gentamicin as prophylaxis for sternal wound infections in different risk groups

OBJECTIVES

In a randomized trial addition of local collagen-gentamicin in the sternal wound reduced the rate of sternal wound infection (SWI) to about 50% compared to intravenous prophylaxis alone. The aim of the present study was to evaluate the economic rationale for its use in every-day clinical practice. This includes the question whether high-risk groups that may have particular benefit should be identified.

DESIGN

For each patient with SWI in the trial the costs attributable to the SWI were calculated. Risk factors for SWI were identified and any heterogeneity of the effect of the prophylaxis examined.

RESULTS

The mean cost of a SWI was about 14500 Euros. A cost effectiveness analysis showed that the prophylaxis was cost saving. The positive net balance was even higher in risk groups. Assignment to the control group, overweight, diabetes, younger age, mammarian artery use, left ventricular ejection fraction <35% and longer operation time were independent risk factors for infection.

CONCLUSION

The addition of local collagen-gentamicin to intravenous antibiotic prophylaxis was dominant, i.e. resulted in both lower costs and fewer wound infections.

[Surgical-site infections following varicose vein surgery according to a continuous series of 408 interventions in a teaching hospital]

OBJECTIVE

To determine the incidence of surgical-site infections (SSI) following varicose vein surgery in the vascular surgery ward of a French teaching hospital.

PATIENTS AND METHODS

A prospective surveillance of SSI was conducted during one year, with a 30-day postoperative follow-up. SSI cases were identified by using the definitions of the Centers for Disease Control (CDC, USA). Data acquisition and analysis were performed with the Epi-Info 6.04 software (CDC).

RESULTS

Three quarters of the 408 included interventions were characterized by a NNIS score equal to 0. All patients underwent a hair removing practice before intervention. Hair removing methods were very heterogeneous and often not in accordance with national recommendations (e.g. mechanic shaving for 44.6% of patients). The incidence of SSI was 1.2% (95% confidence interval=[0.2-2.2]). All infections were identified after hospital discharge. Four infected patients out of five presented obesity or excess weight, and two patients had diabetes mellitus. The mean age of infected patients was significantly higher than non-infected ones (70.4 years versus 52.0; p<0.01). All SSI had consequences like rehospitalization, reintervention, or antimicrobial therapy.

CONCLUSION

According to our results, SSI following varicose vein surgery are scarce and mainly concerned high-risk patients. However, in an aim of prevention, it seems necessary to homogenize hair removing methods in this ward.

Staphylococcus aureus mediastinitis and sternal osteomyelitis following median sternotomy in a rat model

OBJECTIVES

Median sternotomy (MS) wound infections are severe complications causing high morbidity and mortality after cardiac surgery. We aimed to develop a new Staphylococcus aureus mediastinitis and sternal osteomyelitis model in rats that can be used to evaluate the efficacy of new antimicrobial treatments.

METHODS AND RESULTS

A complete MS wound was induced in anaesthetized rats. S. aureus was injected into the sternum. Kinetics of bacterial growth in the sternum (10(7) cfu/sternum) was assessed for histopathology and bacterial counts. A non-infected MS group served as a control. To evaluate antibiotic efficacy, 5 days of intraperitoneal vancomycin therapy (50 mg/kg, twice a day) was initiated 24 h following bacterial challenge. Macroscopic and histological examination confirmed that infection resulted in sternitis and mediastinitis. S. aureus bacterial counts in the sternum were inoculum-dependent, and it was proven that infecting rats with an inoculum of 10(7) cfu/sternum induced mediastinitis and sternal osteomyelitis. At this inoculum, bacterial counts in the infected sternum increased with time, reaching a maximum level of 2 +/- 1 x 10(7) cfu/g of sternum 8-12 days post-infection and then decreased with time to 2 x 10(4) cfu/g of sternum 20 days after infection. Histological changes paralleled bacterial counts. Vancomycin administration showed a protective effect against induction of sternal osteomyelitis; sternums from vancomycin-treated rats showed a significant decrease in S. aureus counts by 0.72 +/- 0.35 log cfu/g compared with untreated controls (P = 0.0162).

CONCLUSIONS

This new rat model of S. aureus sternal osteomyelitis and mediastinitis allows quantitative measurement of bacterial counts in the sternum. This model is reproducible and simple and thus suitable for the evaluation of new antimicrobials and new treatment modalities in MS infections.

Public Health Reporting: The United States Perspective

The release of 2 landmark reports by the Institute of Medicine titled, “To Err Is Human: Building a Safer Health System” and “Crossing the Quality Chasm” were instrumental in the identification of safety and quality issues. Since their release, federal and state programs of public reporting of performance measures have attempted to close the quality gap of care that is inappropriate, not timely, or lacking an evidence base. Cardiac surgery has long been the focus of public scrutiny, and now, as we move from an era of managed care to public reporting, reimbursement for cardiac surgery procedures will be tied to performance. However, the question is whether public reporting and pay for performance will ultimately improve the quality of patient care, safety, and provide the consumer with enough information to make surgeon and institutional choices. Will the cost and focus of achieving perfection with performance standards overshadow any real improvement in clinical outcomes?

A Simulation-Based Evaluation of Methods to Estimate the Impact of an Adverse Event on Hospital Length of Stay

INTRODUCTION

We used agent-based simulation to examine the problem of time-varying confounding when estimating the effect of an adverse event on hospital length of stay. Conventional analytic methods were compared with inverse probability weighting (IPW).

METHODS

A cohort of hospitalized patients, at risk for experiencing an adverse event, was simulated. Synthetic individuals were assigned a severity of illness score on admission. The score varied during hospitalization according to an autoregressive equation. A linear relationship between severity of illness and the logarithm of the discharge rate was assumed. Depending on the model conditions, adverse event status was influenced by prior severity of illness and, in turn, influenced subsequent severity. Conditions were varied to represent different levels of confounding and categories of effect. The simulation output was analyzed by Cox proportional hazards regression and by a weighted regression analysis, using the method of IPW. The magnitude of bias was calculated for each method of analysis.

RESULTS

Estimates of the population causal hazard ratio based on IPW were consistently unbiased across a range of conditions. In contrast, hazard ratio estimates generated by Cox proportional hazards regression demonstrated substantial bias when severity of illness was both a time-varying confounder and intermediate variable. The direction and magnitude of bias depended on how severity of illness was incorporated into the Cox regression model.

CONCLUSIONS

In this simulation study, IPW exhibited less bias than conventional regression methods when used to analyze the impact of adverse event status on hospital length of stay.

The Not-So-Hidden Costs of Surgical Site Infections

Surgical site infections (SSIs) adversely affect approximately 500,000 patients annually, causing immense human suffering and taking a huge financial toll on patients, hospitals, insurance companies, and the government. National organizations have made recommendations for reducing SSIs, and many advances have been made in evidence-based practice recommendations that result in fewer SSIs. Reusable electrocardiogram (ECG) lead wires can be a significant source of infection. One medical center near Richmond, VA, began using a disposable ECG lead wire set and wireless transceiver system and subsequently experienced a 40% decrease in SSIs.

Plasma cefazolin levels during cardiovascular surgery: effects of cardiopulmonary bypass and profound hypothermic circulatory arrest

OBJECTIVES

We sought to assess the effects of cardiopulmonary bypass and profound hypothermic circulatory arrest on plasma cefazolin levels administered for antimicrobial prophylaxis in cardiovascular surgery.

METHODS

Four groups (10 patients per group) were prospectively studied: vascular surgery without cardiopulmonary bypass (group A), cardiac surgery with a cardiopulmonary bypass time of less than 120 minutes (group B), cardiac surgery with a cardiopulmonary bypass time of greater than 120 minutes (group C), and cardiac surgery with cardiopulmonary bypass and profound hypothermic circulatory arrest (group D). Subjects received cefazolin at induction and a second dose before wound closure. Arterial blood samples were obtained preceding cefazolin administration, at skin incision, hourly during the operation, and before redosing. Cefazolin plasma concentrations were determined by using a radial diffusion assay, with Staphylococcus aureus as the indicator microorganism. Cefazolin plasma concentrations were considered noninhibitory at 8 microg/mL or less, intermediate at 16 mug/mL, and inhibitory at 32 microg/mL or greater.

RESULTS

In group A cefazolin plasma concentrations remained greater than 16 microg/mL during the complete surgical procedure. In group B cefazolin plasma concentrations diminished to 16 microg/mL or less in 30% of the patients but remained greater than 8 microg/mL. In group C cefazolin plasma concentrations decreased to less than 16 microg/mL in 60% of patients and were less than 8 microg/mL in 50% of patients. In group D cefazolin plasma concentrations reached 16 microg/mL in 66% of the patients but decreased to 8 microg/mL in only 1 patient.

CONCLUSIONS

For patients undergoing cardiac surgery with a cardiopulmonary bypass time of greater than 120 minutes, a single dose of cefazolin before skin incision with redosing at wound closure does not provide targeted antimicrobial cefazolin plasma levels during the entire surgical procedure. Patients undergoing profound hypothermic circulatory arrest are better protected, but the described protocol of prophylaxis is not optimal.

Postoperative Wundinfektionen

Surgical site infections can be traced to discrepancies in one specific hospital department: the operating suite. Therefore, prevention is often viewed as resting completely on the surgeon. However, the source of micro-organisms responsible for surgical site infections can be endogenous or exogenous. Most infections are believed to be the former, i.e. caused by micro-organisms already resident in the patient's body. Therefore the surgeon can be regarded as suspect only in exceptional cases and usually himself a victim. Prevention is possible not only for exogenous surgical site infection but also many endogenous infections. A multicenter surveillance of infection rates at 130 operative departments participating for at least 4 years in the German National Nosocomial Infection Surveillance System was conducted. A significant 25% reduction in the 3rd year was observed compared with patients who underwent surgery within the 1st year of participation. However, surgeons alone cannot achieve such a decrease, and a team approach is required under most circumstances.

Cost of intensive care unit-acquired bloodstream infections

Intensive care unit-acquired (ICU-acquired) bloodstream infections (BSI) are an important complication of critical illness. The objective of this study was to quantify the excess length of stay, mortality and cost attributable to ICU-acquired BSI. A matched cohort study was conducted in all adult ICUs in the Calgary Health Region between 1 May 2000 and 30 April 2003. One hundred and forty-four patients with ICU-acquired BSI were matched (1:1) to patients without ICU-acquired BSI. Patients with ICU-acquired BSI had a significantly increased median length of ICU stay {15.5 [interquartile range (IQR) 8-26] days vs 12 [IQR 7-18.5] days, P=0.003} and median costs of hospital care [85,137 dollars (IQR 45,740-131,412 dollars) vs 67,879 dollars (IQR 35,043-115,915 dollars, P=0.02) compared with patients without ICU-acquired BSI. The median excess length of ICU stay was two days and the median cost attributable to ICU-acquired BSI was 12,321 dollars per case. Sixty (42%) of the cases died compared with 37 (26%) of the controls [P=0.002, attributable mortality 16%, 95% confidence interval (CI) 5.9-26.0%]. Patients with ICU-acquired BSI were at increased risk for in-hospital death (odds ratio=2.64, 95%CI 1.40-5.29). Among survivor-matched pairs, the median excess lengths of ICU and hospital stay attributable to development of ICU-acquired BSI were two and 13.5 days, respectively, and the attributable cost due to ICU-acquired BSI was 25,155 dollars per case survivor. Critically ill patients who develop ICU-acquired BSI suffer excess morbidity and mortality, and incur significantly increased healthcare costs. These data support expenditures on infection prevention and control programmes and further research into reducing the impact of these infections.

Epidemiologische Grundlagen

Eine Vielzahl an Faktoren tragen zu erhöhten nosokomialen Infektionsraten bei. Die Lebenserwartung und damit der Anteil alter Patienten mit z. T. chronischen Krankheiten steigen stetig an. Medizinische Fortschritte in Diagnostik und Therapie führen zu einer höheren Anzahl der dafür erforderlichen Eingriffe. Es werden immer häufiger immunsupprimierte Patienten (Infektiologie, Rheumatologie, Hämatologie/Onkologie, Transplantation von Organen usw.) behandelt. Das zunehmende Problem der Antibiotikaresistenz von Erregern und die Konsequenzen nosokomialer Infektionen erfordern eine verlässliche Epidemiologie auf diesem Gebiet. Konsequenzen betreffen einerseits Patienten, bei denen es zu einer erhöhten Morbidität und Letalität durch nosokomiale Infektionen kommt, aber andererseits auch das Gesundheitswesen, dem zusätzliche — vermeidbare? — finanzielle Belastungen entstehen.

Evidenzbasierte Empfehlungen, bei denen der jeweilige Einzelfall und die örtlichen Besonderheiten ebenfalls Berücksichtigung finden, sind Voraussetzung für eine sinnvolle und kosteneffektive Vorgehensweise zur Senkung der nosokomialen Infektionsrate. In vielen Studien sind Häufigkeiten und Folgen verschiedener nosokomialer Infektionsarten sowie Maßnahmen zu ihrer Prävention untersucht worden. Um die Qualität solcher Studien und die darauf basierenden Empfehlungen von Experten, die ja oftmals ebenfalls mit Kosten verbunden sind, kritisch beurteilen zu können, ist epidemiologisches Wissen unverzichtbar. Dies beinhaltet selbstverständlich auch die Kenntnis der jeweiligen Erreger solcher Infektionen sowie das Wissen um erregerspezifische Übertragungswege. Die Epidemiologie nosokomialer Infektionen ist daher die Grundlage ihrer eigenen Verbesserung.

»Es gibt nicht Kranke und Gesunde, sondern es gibt nur Untersuchte und nicht Untersuchte« (Johannes Rau, ehemaliger Bundespräsident).

Mortality rate, length of stay and extra cost of sternal surgical site infections following coronary artery bypass grafting in a private medical centre in Turkey

Florence Nightingale Hospital is a 300-bed, university-affiliated, private medical centre with a large open heart surgery programme in Istanbul, Turkey. In this study, the mortality rates, lengths of stay (LOS) and extra costs of patients with deep sternal surgical site infections (DSSSIs) and superficial sternal surgical site infections (SSSSIs) following coronary artery bypass grafting (CABG) were determined from January 1999 to December 2002. Group I included 52 patients with DSSSIs, Group II included 36 patients with SSSSIs and Group III included 88 controls. The controls were selected at random from patients operated within the same year, with the same sex and age within five years, but who had not developed infection. Mortality rates in Groups I, II and III were 19.2%, 0% and 4.5%, respectively; the mortality rate in Group I was significantly different from that in Groups II and III (P<0.005). LOS was 47, 33 and 12 days for Groups I, II and III, respectively, and LOS was statistically different for each group (P<0.005). The costs of extra LOS, antibiotics, and radiological, microbiologial and other laboratory examinations for Groups I and II were US$6850.93 and US$3740.58, respectively. Both DSSSI and SSSSI following CABG extended the LOS and increased the cost, and DSSSI was significantly associated with a high mortality rate. These results suggest the need for improved infection control measures to reduce SSSIs following CABG. As an important component of the extra cost is the extra LOS, it is essential to shorten this period. This may be particularly applicable in patients with SSSSIs.

Fatores predisponentes à infecção do sítio cirúrgico em gastrectomia

A presente investigação teve como objetivo identificar os fatores predisponentes à infecção do sítio cirúrgico relacionados ao procedimento cirúrgico no paciente submetido à cirurgia eletiva de gastrectomia, potencialmente contaminada, na especialidade de Gastrocirurgia, no período compreendido entre 1998 a 2002, em um hospital público do interior paulista. Realizou-se um estudo retrospectivo, por meio do levantamento de informações contidas nos prontuários médicos, utilizando-se para a análise estatística dos dados os testes não paramétricos: Mann-Whitney (variáveis quantitativas) e coeficiente de contingência (variáveis qualitativas). Em 181 casos investigados, detectou-se a ocorrência de infecção do sítio cirúrgico em 17 situações (9,4%); sendo 23,6% classificadas como infecção incisional superficial; 52,9% infecção incisional profunda e 23,6% infecção de órgão/espaço. As variáveis período de internação pós-operatório, período de internação total, duração da cirurgia, tempo de sondagem vesical de demora apresentaram diferença estatisticamente significante entre os grupos com e sem infecção.

Surgical site infection - a European perspective of incidence and economic burden

This retrospective review of reported surgical site infection (SSI) rates in Europe was undertaken to obtain an estimated scale of the problem and the associated economic burden. Preliminary literature searches revealed incomplete datasets when applying the National Nosocomial Infection Surveillance System criteria. Following an expanded literature search, studies were selected according to the number of parameters reported, from those identified as critical for accurate determination of SSI rates. Forty-eight studies were analysed. None of the reviewed studies recorded all the data necessary to enable a comparative assessment of the SSI rate to be undertaken. The estimated range from selected studies analysed varied widely from 1.5-20% - a consequence of inconsistencies in data collection methods, surveillance criteria and wide variations in the surgical procedures investigated - often unspecified. SSIs contribute greatly to the economic costs of surgical procedures - estimated range: 1.47-19.1 billion Euro dollars. The analysis suggests that the true rate of SSIs, currently unknown, is likely to have been previously under-reported. Consequently, the associated economic burden is also likely to be underestimated. A significant improvement in study design, data collection, analysis and reporting will be necessary to ensure that SSI baseline rates are more accurately assessed to enable the evaluation of future cost-effective measures.

Glycopeptides are no more effective than beta-lactam agents for prevention of surgical site infection after cardiac surgery: a meta-analysis

A meta-analysis was performed to investigate whether a switch from beta-lactams to glycopeptides for cardiac surgery prophylaxis should be advised. Results of 7 randomized trials (5761 procedures) that compared surgical site infections (SSIs) in subjects receiving glycopeptide prophylaxis with SSIs in those who received beta -lactam prophylaxis were pooled. Neither agent proved to be superior for prevention of the primary outcome, occurrence of SSI at 30 days (risk ratio [RR], 1.14; 95% confidence interval [CI], 0.91-1.42). In subanalyses, beta-lactams were superior to glycopeptides for prevention of chest SSIs (RR, 1.47; 95% CI, 1.11-1.95) and approached superiority for prevention of deep-chest SSIs (RR, 1.33; 95% CI, 0.91-1.94) and SSIs caused by gram-positive bacteria (RR, 1.36; 95% CI, 0.98-1.91). Glycopeptides approached superiority to beta-lactams for prevention of leg SSIs (RR, 0.77; 95% CI, 0.58-1.01) and were superior for prevention of SSIs caused by methicillin-resistant gram-positive bacteria (RR, 0.54; 95% CI, 0.33-0.90). Standard prophylaxis for cardiac surgery should continue to be beta-lactams in most circumstances.

Modeling the costs of hospital-acquired infections in New Zealand

OBJECTIVE

To model the economic costs of hospital-acquired infections (HAIs) in New Zealand, by type of HAI.

DESIGN

Monte Carlo simulation model.

SETTING

Auckland District Health Board Hospitals (DHBH), the largest publicly funded hospital group in New Zealand supplying secondary and tertiary services. Costs are also estimated for predicted HAIs in admissions to all hospitals in New Zealand.

PATIENTS

All adults admitted to general medical and general surgical services.

METHOD

Data on the number of cases of HAI were combined with data on the estimated prolongation of hospital stay due to HAI to produce an estimate of the number of bed days attributable to HAI. A cost per bed day value was applied to provide an estimate of the economic cost. Costs were estimated for predicted infections of the urinary tract, surgical wounds, the lower and upper respiratory tracts, the bloodstream, and other sites, and for cases of multiple sites of infection. Sensitivity analyses were undertaken for input variables.

RESULTS

The estimated costs of predicted HAIs in medical and surgical admissions to Auckland DHBH were dollar 10.12 (US dollar 4.56) million and dollar 8.64 (US dollar 3.90) million, respectively. They were dollar 51.35 (US dollar 23.16) million and dollar 85.26 (US dollar 38.47) million, respectively, for medical and surgical admissions to all hospitals in New Zealand.

CONCLUSIONS

The method used produces results that are less precise than those of a specifically designed study using primary data collection, but has been applied at a lower cost The estimated cost of HAIs is substantial but only a proportion of infections can be avoided. Further work is required to identify the most cost-effective strategies for the prevention of HAI.