- Email: [email protected]
Evaluation of the costs and benefits of reducing hospital infection
Journal
of Hospital
Infection
Evaluation
(1991)
18 (Supplement
A), 85-93
of the costs and benefits hospital infection M. F. Drummond
Centre for Health 5DD and “Health
of reducing
and L. M. Davies*
of York, Heslington, York YOl Economics, University Services Management Centre, University of Birmingham, Birmingham, UK
Summary: The techniques of economic evaluation have now been widely applied in health care. These techniques assess the value for money from interventions by comparing their costs and consequences. Since measures to reduce hospital infection normally result in costs they should, in principle, be subjected to economic evaluation. This paper outlines the essential elements of economic evaluation and distinguishes between different forms of analysis. It also discusses a number of evaluations of infection control measures undertaken to date. The recurring methodological weaknesses in current studies are identified and improvements suggested. Finally, the practical relevance of such studies in the current cost-conscious health care environment is discussed. Keywords: tion.
Cost-effectiveness
analysis;
economic
evaluation;
hospital
infec-
Introduction The available resources for health care are increasingly stretched in the face of competing demands for their use. Therefore, governments and other third party payers have taken initiatives to increase the efficiency or cost-effectiveness of health care provision. The precise measures vary from country to country, but in the hospital sector they usually involve a combination of budgetary and organizational changes. First, there is a trend towards prospective payment systems (PPS) or global budgets for hospitals, in place of the retrospective reimbursement of hospital expenditure according to a per diem rate. The most well-known example of this is the approach based on diagnosis-related groups (DRGs) pioneered by Medicare in the USA. Secondly, hospital-based drugs formularies have become more widespread, accompanied by a closer monitoring of pharmacy expenditure. Thirdly, in some settings, such as the UK, clinical teams have been encouraged to accept responsibility for a budget covering the costs of care for patients admitted in their specialty. The object is to encourage more careful use of clinical resources (e.g. for Correspondence 0195-6701/91/06A085+09
to: Professor
M.
F. Drummond 0 1991 The Hospital
X03.00/0
85
Infection
Society
86
M. F. Drummond
and L. M. Davies
tests, drugs and bed space) by allowing clinical teams to re-deploy a portion of the resources saved to the benefit of other patients.’ In this cost-conscious environment any treatment or programme requiring a commitment of resources is likely to come under closer scrutiny. Procedures to reduce hospital infection are no exception: some measures, which seek to provide a better standard of hygiene, require manpower, equipment or supplies. Other measures, such as the use of antibiotics to reduce perioperative infections clearly add to pharmaceutical expenditure. Therefore, assessments are required of whether the benefits of these investments justify the costs. In addition, even if a budget for hospital infection control has been established, it is important to assess whether this is being spent in the most cost-effective way possible.2 Methods
of economic
evaluation
Economic evaluation is a family of techniques, all of which assess the value for money from health care interventions by comparing their costs with their consequences. 3 There are a number of forms of evaluation, illustrated in Figure 1. The inputs to, or costs of, a health care programme or intervention include the direct costs of providing care’ and the indirect costs (in production losses) arising when individuals are withdrawn from the workforce to be given therapy (C,). Finally, there may also be intangible costs (C,), in pain or suffering, associated with the intervention. The simplest form of analysis, cost-analysis or cost-minimization analysis, either assumes or demonstrates that the clinical outcomes of two or more interventions are equivalent. Therefore, the choice between them rests solely on costs. Many of the economic evaluations of methods of reducing hospital infection fall into this category. However, not all interventions reduce the overall cost and therefore any additional costs need to be compared with a measure of output. One approach would be to relate costs to the consequences measured in the most obvious natural units or ‘effects’. For example, life-saving interventions are often compared, in a cost-effectiveness analysis, in terms of their cost per life-year gained. Although one of the potential sequelae of hospital infection is death, a cost-effectiveness analysis of hospital control strategies is more likely to consider cost per infection, or infection day averted. The main advantage of cost-effectiveness analysis is its simplicity. However, in assessing priorities between infection control measures and other health care interventions, or even among infection control measures, the chosen unit of output (e.g. infection day) may not be sufficiently generalizable. This is why analysts sometimes attempt to express all the consequences in money terms, in a cost-benefit analysis. Full cost-benefit analyses are rarely carried out in health care because of the problems of quantifying the intangible costs and benefits of health (C, and B, in Figure 1). However, some evaluations in the hospital infection control field represent limited cost-benefit analyses by
Costs
Health
Inputs Resources
and benefits
of hospital
outputs
care Health
programme
consumed
Possible
(health C,=lndirect
C,=lntangible
units
losses)
costs
B
Associated economic
effects)
1
costs
(production
I
In natural
costs
improvements
measurements
EI
C C,=Direct
87
infection
benefits
U
In utility
B,=Direct
($) benefits
units
(quality adjusted
B,=lndirect
benefits
(production
gains)
life-years) B,=lntangible
Figure
1. Components
of economic
benefits
evaluation.
considering items C, and B, in Figure 1. For example, Shapiro et ~1.~ showed that in patients undergoing abdominal hysterectomy, those receiving antimicrobial prophylaxis (cefazolin) cost an average $102 less than those receiving a placebo in a controlled trial. This is because the additional costs of the intervention (C,) were more than balanced by the savings in other health care resources required to treat the perioperative infections (direct benefits, B,). An alternative to cost-benefit analysis is cost-utility analysis, where a generic measure of health status such as the quality adjusted life-year is used to express the consequences of an intervention. Cost-utility analysis has been gaining popularity in recent years because of the need to compare a range of interventions and the obvious difficulties of measuring all health consequences in money terms, particularly the intangible benefits (B3) (see Torrance & Zipursky’ and Williams6 for examples of rankings of health care interventions by cost per QALY). The significance of cost-utility analysis in the evaluation of hospital infection
88
M. F. Drummond
and L. M. Davies
control measures is hard to gauge. It depends partly on whether proponents of control measures are happy to construct their arguments based mainly on cost savings, or whether they wish to argue that it is worth bearing additional costs because of improved quality of life of the patient. Assessment
of current
studies
Drummond et ~1.~ identified ten methodological features of a well-conducted economic appraisal in health care. Not all of these are directly relevant to the assessment of alternatives in hospital infection control (e.g. the adjustment of costs and consequences for differential timing). The methodological issues of concern for hospital infection control are discussed below, illustrated by studies already undertaken.
Choice of viewpoint There are a number of potential viewpoints for an evaluation of hospital infection control measures: the infection control department itself, the hospital, the patient, the government or third party payer, or society.7 Daschner2 points out that the various viewpoints sometimes conflict, in that ‘hospital administrations in Germany are in no way interested in reducing nosocomial infection rates and thus the length of hospitalization because the insurance companies pay the same amount of money for each day of hospitalization’. Economists usually argue for a broad viewpoint, such as that of society, when evaluating health care options since, as in the example above, attention to more restrictive viewpoints can lead to inefficiency. Many of the evaluations reported in the literature consider costs and benefits to the hospital only. However, any concerns over this are likely to subside as the financial incentives to hospitals change. Under the new prospective reimbursement schemes the interests of the hospital more closely mirror those of the third party payer. Therefore, an evaluation considering costs and benefits to the third party payer will often suffice. If such an evaluation suggests that infection control gives good value for money, consideration of the patient’s costs and benefits will usually merely confirm the result. However, if such an evaluation demonstrates a net cost to the third party payer this will have to be compared, in a cost-utility or cost-benefit analysis, with the benefits to the patient.
Selection of alternatives for comparison There are many possible options within including ‘doing nothing’. Daschner2 provides setting priorities for evaluation, focusing on the costly patients and most costly patient care. literature compare alternative drug regimens.4’8 improvements in surgical technique or hygiene
hospital infection control, a pragmatic approach to most costly infections, most Many of the studies in the Others compare drugs with measures.9a’0 One difficulty
Costs
and benefits
of hospital
infection
89
is that various infection control measures are complementary to one another, as well as being alternatives. Another difficulty is in the assessment of the costs and benefits of an integrated infection control strategy in the hospital. In an analogous field, occupational health, Atherley et al.” concluded that it was only feasible to analyse the separate components from an economic viewpoint. However, in general most of the studies in the literature state the alternatives for evaluation clearly. Range of costs and benefits considered The relevant range of costs and benefits in an economic evaluation is largely a function of viewpoint. However, a number of additional points can be made. First, in evaluating drug prophylaxis it is important to consider not only the costs of the drugs themselves, but also the costs of administration (e.g. iv infusion) and the costs of treating side-effects.‘*,13 Secondly, although most studies of hospital infection confine themselves to costs incurred in the hospital Mugford et ~1.‘~ point out that there may be costs post discharge relevant to an evaluation undertaken from a broad societal viewpoint. For example, patients having a hospital infection may require additional family support when discharged home. On the other hand, a patient who, having no complications due to infection, is discharged very early may require community nursing (e.g. to change wound dressings). Had the patient remained longer in hospital these costs would have fallen on the hospital budget. Finally, although most of the studies in the literature consider direct costs and benefits (C, and B, in Figure 1) Persson et a1.l’ acknowledge that there are other components of the value of reducing infection. When they included in their analysis an amount to reflect the value of loss of health (B2 and B, in Figure l), an economic optimum was established that allowed selection of a more costly method of prophylaxis. Assessment of costs and benefits Economic evaluation should be based on good technical (clinical) evidence of the effectiveness of health care interventions. In the field of hospital infection control there are examples of economic evaluation based on a randomized controlled clinical triaJ4 or on synthesis of clinical evidence from a number of studies; ‘zl* this is to be encouraged. Haley et aZ.14 and Daschner* point out that controlled study is required not only for assessment of clinical outcomes (e.g. number and type of infection) but also for the economic outcomes (e.g. length of hospital stay). For example, studies show that physicians’ estimates of the additional hospital stay required as a result of infection are much lower than the actual values. However, while there are undoubted benefits of undertaking economic analysis alongside controlled clinical trials,” a number of methodological complexities arise. l6 In particular, owing to the large variability in hospital large sample sizes may be required to detect a difference at the stay,
90
M. F. Drummond
and
L. M. Davies
conventional levels of statistical significance. In addition, some infection control strategies, such as improving the quality of hospital buildings or ventilation, may not be so amenable to prospective randomized designs. Therefore, before-and-after studies or matched controls may have to be used. Hubner et ~1.” report the result of a before-and-after study of a move to new facilities, which showed no difference in infection rates. Incremental analysis Economists argue that the relevant costs and benefits in a comparison of alternative strategies are those ‘at the margin’. Put simply, in moving from one strategy to another the relevant questions are ‘how much extra do we gain in benefits?’ and ‘how much extra do we incur in costs?‘. This concept has relevance to the evaluation of hospital infection control in at least two ways. First, a key issue in control is that of ‘how far’ does one go in reducing risk. For example, some infection control measures may be simple and inexpensive to implement and may be effective in reducing the level of infection. Then, in order to reduce infection further, more expensive measures may have to be employed, such as the selective or routine use of antimicrobial agents. More expensive drugs may be even more effective. However, the extra (marginal) costs of each stage of control are likely to increase; also the marginal benefits are likely to remain constant or decline slightly, as in Figure 2. Therefore, the economically optimal level of control is at the point (X) where the two curves cross. A level of control less than this would be suboptimal because the extra benefits of more control would be greater than the costs. A level of control greater than X would be suboptimal because the extra benefits would be lower than the extra costs. This general concept was employed by Persson et aZ.,” who related the cost of prophylaxis to the value of infection control, as measured by the cost of a re-operation in total joint replacement and an assumed value for loss of health. The second way in which the concept of the margin is relevant to the evaluation of infection control measures relates to the estimation of the savings from reduced infection. For example, if it could be demonstrated that the length of a patient stay is shortened, the average daily cost of a bed is not saved unless the bed can be fully deployed to the benefit of other patients or hospital bed capacity reduced. The marginal savings may be quite small if the bed remains unoccupied. This stresses the need for implementation of measures that will realize the potential savings from reduced infection. Testing the sensitivity of study results Often a number of assumptions are made when undertaking an economic evaluation. These may relate either to the clinical evidence or to the
Costs
and
benefits
of hospital
infection
91
X Level
Figure
of
2. Cost and benefit
control
of risk
vs. the level of control
of risk.
estimation of costs. Therefore, it is commonplace, in economic evaluations, to undertake a sensitivity analysis, where the impact on study results of varying the estimated values of key parameters is explored. For example, in their study of antimicrobial therapy for serious infection, Weinstein et LzZ.~ varied assumptions about the efficacy of regimens, clinical practice in relation to culture results, drug process, drug administration costs and toxicity rates.
Practical
relevance
of studies
The brief review above suggests that it is possible to apply the methods of economic evaluation to infection control measures. A number of such studies have already been undertaken. Many have employed good methodology, although methodological improvements can be identified. However, even if studies are well-conducted, their practical relevance needs to be assessed. Clearly the health care setting, in particular the method of reimbursing hospitals, has a major impact. Currently in the UK there is no direct financial advantage to the hospital of reducing inpatient stay by controlling infection, as no extra revenue is received if more patients are treated (this situation will shortly change when contracts for hospital services are established as a result of the UK Government’s reforms of the National Health Service.‘*) However, even under the present arrangements a hospital
M. F. Drummond
92
and L. M. Davies
can incur substantial additional costs if a severe outbreak of infection occurs. Another key consideration is the legal setting in which the hospital operates. In the USA it has been argued that under the rules of joint and several liability, neither DRGs nor formulary committee edict will ever constitute a defence for lowering standards of patient care.” The extent to which legal considerations promote or hinder the implementation of cost-effective practices in this area is not clear. Finally, it is clear that whatever the financial, clinical and legal background, actions need to be taken in order to encourage the adoption of cost-effective practices. At the clinical level it is important to establish guidelines as a result of study findings.2 At a management level, actions may need to be taken so that the hospital can reap the benefits of infection control. These may include providing adequate support to infection control activities and formulary committees, and rationalizing bed provision in the hospital. The Centre for Health Economics is grateful to the Merck Company Foundation for a gift to explore the links between economic analysis and medical research. In addition, the European Community has provided funds for a Concerted Action on the Methodology of Economic Appraisal of Health Technology.
References 1. Buxton 2. 3. 4. 5. 6. 7. 8‘ 9. 10. 11. 12. 13. 14.
MJ et al. Resource Management: Progress in the Pilot Sites. London: Department of Health 1989. Daschner F. Cost-effectiveness in hospital infection control-lessons for the 1990s. J Hosp Infect 1989; 13: 325-336. Drummond MF, Stoddart GL, Torrance GW. Methods for the Economic Evaluation of Health Care Programmes. Oxford: Oxford University Press 1987. Shapiro M, Schoenbaum SC, Tager IB et al. Cost benefit analysis of anti-microbial prophylaxis in abdominal and vaginal hysterectomy. JAMA 1983; 249: 1290-1294. Torrance GW, Zipursky A. Cost-effectiveness of antepartum prevention of RH immunization. Clin Perinatol 1984; 11: 267-281. Williams A. Economics of coronary bypass grafting. Br MedJ# 1985; 291: 326-329. Currie E, Maynard A. The economics of hospital acquired infection. Discussion Paper 56. University of York, Centre for Health Economics and Health Economics Consortium, 1989. Weinstein MC, Leighton Read J, Mackay DN et al. Cost-effective choice of antimicrobial therapy for serious infections. J Gen Intern Med 1986; 1: 352-363. Platt R, Polk BE, Murdock B et al. Prevention of catheter-associated urinary tract infection: a cost benefit analysis. Infect Control Hasp Epidemiol 1989; 10: 6&64. Persson U, Montgomery F, Carlsson A et al. How far does prophylaxis against infection in total joint replacement offset its cost? Br MedJ 1988; 296: 99-102. Atherley G, Cale RW, Drummond MF et al. An approach to the financial evaluation of occupational health services. r Sot Occup Med 1976; 26: 21-30. Mugford M, Kingston J, Chalmers I. Reducing the incidence of infection after caesarian section: implications of prophylaxis with antibiotics for hospital resources. Br Med J 1989; 299: 1000-1006. O’Leary MP. Economic considerations in management of complicated urinary tract infections. Urology (Suppl. 1) 1990; 35: 22-24. Haley RW, Schaberg DR, Von Allman SD et al. Estimating the extra charges and prolongation of hospitalization due to nosocomial infections: a comparison of methods. r Infect Dis 1980; 141: 248-257.
Costs
and benefits
of hospital
infection
93
15. Drummond MF, Stoddart GL. Economic analysis and clinical trials. Con Clin Trials 1984; 5: 115-128. 16. Drummond MF, Davies LM. Economic analysis alongside clinical trials: revisiting the methodological issues. Paper presented at the Joint Meeting of the European Health Economics Societies, Barcelona, 21-23 September 1989. 17. Hubner J, Frank U, Kappstein I et al. Influence of architectural design on nosocomial infections in intensive care units-a prospective 2-year analysis. Intensive Care Med (in press). 18. Department of Health. Working for Patients. London: Department of Health. 19. Schiefe RT, Cox CE, McCabe RE et al. Norfloxacin versus best parenteral therapy in treatment of moderate to serious multiply-resistant, nosocomial urinary tract infections: a pharmacoeconomic analysis. Urology 1988; 32 (Suppl. 3): 2430.
of Hospital
Infection
Evaluation
(1991)
18 (Supplement
A), 85-93
of the costs and benefits hospital infection M. F. Drummond
Centre for Health 5DD and “Health
of reducing
and L. M. Davies*
of York, Heslington, York YOl Economics, University Services Management Centre, University of Birmingham, Birmingham, UK
Summary: The techniques of economic evaluation have now been widely applied in health care. These techniques assess the value for money from interventions by comparing their costs and consequences. Since measures to reduce hospital infection normally result in costs they should, in principle, be subjected to economic evaluation. This paper outlines the essential elements of economic evaluation and distinguishes between different forms of analysis. It also discusses a number of evaluations of infection control measures undertaken to date. The recurring methodological weaknesses in current studies are identified and improvements suggested. Finally, the practical relevance of such studies in the current cost-conscious health care environment is discussed. Keywords: tion.
Cost-effectiveness
analysis;
economic
evaluation;
hospital
infec-
Introduction The available resources for health care are increasingly stretched in the face of competing demands for their use. Therefore, governments and other third party payers have taken initiatives to increase the efficiency or cost-effectiveness of health care provision. The precise measures vary from country to country, but in the hospital sector they usually involve a combination of budgetary and organizational changes. First, there is a trend towards prospective payment systems (PPS) or global budgets for hospitals, in place of the retrospective reimbursement of hospital expenditure according to a per diem rate. The most well-known example of this is the approach based on diagnosis-related groups (DRGs) pioneered by Medicare in the USA. Secondly, hospital-based drugs formularies have become more widespread, accompanied by a closer monitoring of pharmacy expenditure. Thirdly, in some settings, such as the UK, clinical teams have been encouraged to accept responsibility for a budget covering the costs of care for patients admitted in their specialty. The object is to encourage more careful use of clinical resources (e.g. for Correspondence 0195-6701/91/06A085+09
to: Professor
M.
F. Drummond 0 1991 The Hospital
X03.00/0
85
Infection
Society
86
M. F. Drummond
and L. M. Davies
tests, drugs and bed space) by allowing clinical teams to re-deploy a portion of the resources saved to the benefit of other patients.’ In this cost-conscious environment any treatment or programme requiring a commitment of resources is likely to come under closer scrutiny. Procedures to reduce hospital infection are no exception: some measures, which seek to provide a better standard of hygiene, require manpower, equipment or supplies. Other measures, such as the use of antibiotics to reduce perioperative infections clearly add to pharmaceutical expenditure. Therefore, assessments are required of whether the benefits of these investments justify the costs. In addition, even if a budget for hospital infection control has been established, it is important to assess whether this is being spent in the most cost-effective way possible.2 Methods
of economic
evaluation
Economic evaluation is a family of techniques, all of which assess the value for money from health care interventions by comparing their costs with their consequences. 3 There are a number of forms of evaluation, illustrated in Figure 1. The inputs to, or costs of, a health care programme or intervention include the direct costs of providing care’ and the indirect costs (in production losses) arising when individuals are withdrawn from the workforce to be given therapy (C,). Finally, there may also be intangible costs (C,), in pain or suffering, associated with the intervention. The simplest form of analysis, cost-analysis or cost-minimization analysis, either assumes or demonstrates that the clinical outcomes of two or more interventions are equivalent. Therefore, the choice between them rests solely on costs. Many of the economic evaluations of methods of reducing hospital infection fall into this category. However, not all interventions reduce the overall cost and therefore any additional costs need to be compared with a measure of output. One approach would be to relate costs to the consequences measured in the most obvious natural units or ‘effects’. For example, life-saving interventions are often compared, in a cost-effectiveness analysis, in terms of their cost per life-year gained. Although one of the potential sequelae of hospital infection is death, a cost-effectiveness analysis of hospital control strategies is more likely to consider cost per infection, or infection day averted. The main advantage of cost-effectiveness analysis is its simplicity. However, in assessing priorities between infection control measures and other health care interventions, or even among infection control measures, the chosen unit of output (e.g. infection day) may not be sufficiently generalizable. This is why analysts sometimes attempt to express all the consequences in money terms, in a cost-benefit analysis. Full cost-benefit analyses are rarely carried out in health care because of the problems of quantifying the intangible costs and benefits of health (C, and B, in Figure 1). However, some evaluations in the hospital infection control field represent limited cost-benefit analyses by
Costs
Health
Inputs Resources
and benefits
of hospital
outputs
care Health
programme
consumed
Possible
(health C,=lndirect
C,=lntangible
units
losses)
costs
B
Associated economic
effects)
1
costs
(production
I
In natural
costs
improvements
measurements
EI
C C,=Direct
87
infection
benefits
U
In utility
B,=Direct
($) benefits
units
(quality adjusted
B,=lndirect
benefits
(production
gains)
life-years) B,=lntangible
Figure
1. Components
of economic
benefits
evaluation.
considering items C, and B, in Figure 1. For example, Shapiro et ~1.~ showed that in patients undergoing abdominal hysterectomy, those receiving antimicrobial prophylaxis (cefazolin) cost an average $102 less than those receiving a placebo in a controlled trial. This is because the additional costs of the intervention (C,) were more than balanced by the savings in other health care resources required to treat the perioperative infections (direct benefits, B,). An alternative to cost-benefit analysis is cost-utility analysis, where a generic measure of health status such as the quality adjusted life-year is used to express the consequences of an intervention. Cost-utility analysis has been gaining popularity in recent years because of the need to compare a range of interventions and the obvious difficulties of measuring all health consequences in money terms, particularly the intangible benefits (B3) (see Torrance & Zipursky’ and Williams6 for examples of rankings of health care interventions by cost per QALY). The significance of cost-utility analysis in the evaluation of hospital infection
88
M. F. Drummond
and L. M. Davies
control measures is hard to gauge. It depends partly on whether proponents of control measures are happy to construct their arguments based mainly on cost savings, or whether they wish to argue that it is worth bearing additional costs because of improved quality of life of the patient. Assessment
of current
studies
Drummond et ~1.~ identified ten methodological features of a well-conducted economic appraisal in health care. Not all of these are directly relevant to the assessment of alternatives in hospital infection control (e.g. the adjustment of costs and consequences for differential timing). The methodological issues of concern for hospital infection control are discussed below, illustrated by studies already undertaken.
Choice of viewpoint There are a number of potential viewpoints for an evaluation of hospital infection control measures: the infection control department itself, the hospital, the patient, the government or third party payer, or society.7 Daschner2 points out that the various viewpoints sometimes conflict, in that ‘hospital administrations in Germany are in no way interested in reducing nosocomial infection rates and thus the length of hospitalization because the insurance companies pay the same amount of money for each day of hospitalization’. Economists usually argue for a broad viewpoint, such as that of society, when evaluating health care options since, as in the example above, attention to more restrictive viewpoints can lead to inefficiency. Many of the evaluations reported in the literature consider costs and benefits to the hospital only. However, any concerns over this are likely to subside as the financial incentives to hospitals change. Under the new prospective reimbursement schemes the interests of the hospital more closely mirror those of the third party payer. Therefore, an evaluation considering costs and benefits to the third party payer will often suffice. If such an evaluation suggests that infection control gives good value for money, consideration of the patient’s costs and benefits will usually merely confirm the result. However, if such an evaluation demonstrates a net cost to the third party payer this will have to be compared, in a cost-utility or cost-benefit analysis, with the benefits to the patient.
Selection of alternatives for comparison There are many possible options within including ‘doing nothing’. Daschner2 provides setting priorities for evaluation, focusing on the costly patients and most costly patient care. literature compare alternative drug regimens.4’8 improvements in surgical technique or hygiene
hospital infection control, a pragmatic approach to most costly infections, most Many of the studies in the Others compare drugs with measures.9a’0 One difficulty
Costs
and benefits
of hospital
infection
89
is that various infection control measures are complementary to one another, as well as being alternatives. Another difficulty is in the assessment of the costs and benefits of an integrated infection control strategy in the hospital. In an analogous field, occupational health, Atherley et al.” concluded that it was only feasible to analyse the separate components from an economic viewpoint. However, in general most of the studies in the literature state the alternatives for evaluation clearly. Range of costs and benefits considered The relevant range of costs and benefits in an economic evaluation is largely a function of viewpoint. However, a number of additional points can be made. First, in evaluating drug prophylaxis it is important to consider not only the costs of the drugs themselves, but also the costs of administration (e.g. iv infusion) and the costs of treating side-effects.‘*,13 Secondly, although most studies of hospital infection confine themselves to costs incurred in the hospital Mugford et ~1.‘~ point out that there may be costs post discharge relevant to an evaluation undertaken from a broad societal viewpoint. For example, patients having a hospital infection may require additional family support when discharged home. On the other hand, a patient who, having no complications due to infection, is discharged very early may require community nursing (e.g. to change wound dressings). Had the patient remained longer in hospital these costs would have fallen on the hospital budget. Finally, although most of the studies in the literature consider direct costs and benefits (C, and B, in Figure 1) Persson et a1.l’ acknowledge that there are other components of the value of reducing infection. When they included in their analysis an amount to reflect the value of loss of health (B2 and B, in Figure l), an economic optimum was established that allowed selection of a more costly method of prophylaxis. Assessment of costs and benefits Economic evaluation should be based on good technical (clinical) evidence of the effectiveness of health care interventions. In the field of hospital infection control there are examples of economic evaluation based on a randomized controlled clinical triaJ4 or on synthesis of clinical evidence from a number of studies; ‘zl* this is to be encouraged. Haley et aZ.14 and Daschner* point out that controlled study is required not only for assessment of clinical outcomes (e.g. number and type of infection) but also for the economic outcomes (e.g. length of hospital stay). For example, studies show that physicians’ estimates of the additional hospital stay required as a result of infection are much lower than the actual values. However, while there are undoubted benefits of undertaking economic analysis alongside controlled clinical trials,” a number of methodological complexities arise. l6 In particular, owing to the large variability in hospital large sample sizes may be required to detect a difference at the stay,
90
M. F. Drummond
and
L. M. Davies
conventional levels of statistical significance. In addition, some infection control strategies, such as improving the quality of hospital buildings or ventilation, may not be so amenable to prospective randomized designs. Therefore, before-and-after studies or matched controls may have to be used. Hubner et ~1.” report the result of a before-and-after study of a move to new facilities, which showed no difference in infection rates. Incremental analysis Economists argue that the relevant costs and benefits in a comparison of alternative strategies are those ‘at the margin’. Put simply, in moving from one strategy to another the relevant questions are ‘how much extra do we gain in benefits?’ and ‘how much extra do we incur in costs?‘. This concept has relevance to the evaluation of hospital infection control in at least two ways. First, a key issue in control is that of ‘how far’ does one go in reducing risk. For example, some infection control measures may be simple and inexpensive to implement and may be effective in reducing the level of infection. Then, in order to reduce infection further, more expensive measures may have to be employed, such as the selective or routine use of antimicrobial agents. More expensive drugs may be even more effective. However, the extra (marginal) costs of each stage of control are likely to increase; also the marginal benefits are likely to remain constant or decline slightly, as in Figure 2. Therefore, the economically optimal level of control is at the point (X) where the two curves cross. A level of control less than this would be suboptimal because the extra benefits of more control would be greater than the costs. A level of control greater than X would be suboptimal because the extra benefits would be lower than the extra costs. This general concept was employed by Persson et aZ.,” who related the cost of prophylaxis to the value of infection control, as measured by the cost of a re-operation in total joint replacement and an assumed value for loss of health. The second way in which the concept of the margin is relevant to the evaluation of infection control measures relates to the estimation of the savings from reduced infection. For example, if it could be demonstrated that the length of a patient stay is shortened, the average daily cost of a bed is not saved unless the bed can be fully deployed to the benefit of other patients or hospital bed capacity reduced. The marginal savings may be quite small if the bed remains unoccupied. This stresses the need for implementation of measures that will realize the potential savings from reduced infection. Testing the sensitivity of study results Often a number of assumptions are made when undertaking an economic evaluation. These may relate either to the clinical evidence or to the
Costs
and
benefits
of hospital
infection
91
X Level
Figure
of
2. Cost and benefit
control
of risk
vs. the level of control
of risk.
estimation of costs. Therefore, it is commonplace, in economic evaluations, to undertake a sensitivity analysis, where the impact on study results of varying the estimated values of key parameters is explored. For example, in their study of antimicrobial therapy for serious infection, Weinstein et LzZ.~ varied assumptions about the efficacy of regimens, clinical practice in relation to culture results, drug process, drug administration costs and toxicity rates.
Practical
relevance
of studies
The brief review above suggests that it is possible to apply the methods of economic evaluation to infection control measures. A number of such studies have already been undertaken. Many have employed good methodology, although methodological improvements can be identified. However, even if studies are well-conducted, their practical relevance needs to be assessed. Clearly the health care setting, in particular the method of reimbursing hospitals, has a major impact. Currently in the UK there is no direct financial advantage to the hospital of reducing inpatient stay by controlling infection, as no extra revenue is received if more patients are treated (this situation will shortly change when contracts for hospital services are established as a result of the UK Government’s reforms of the National Health Service.‘*) However, even under the present arrangements a hospital
M. F. Drummond
92
and L. M. Davies
can incur substantial additional costs if a severe outbreak of infection occurs. Another key consideration is the legal setting in which the hospital operates. In the USA it has been argued that under the rules of joint and several liability, neither DRGs nor formulary committee edict will ever constitute a defence for lowering standards of patient care.” The extent to which legal considerations promote or hinder the implementation of cost-effective practices in this area is not clear. Finally, it is clear that whatever the financial, clinical and legal background, actions need to be taken in order to encourage the adoption of cost-effective practices. At the clinical level it is important to establish guidelines as a result of study findings.2 At a management level, actions may need to be taken so that the hospital can reap the benefits of infection control. These may include providing adequate support to infection control activities and formulary committees, and rationalizing bed provision in the hospital. The Centre for Health Economics is grateful to the Merck Company Foundation for a gift to explore the links between economic analysis and medical research. In addition, the European Community has provided funds for a Concerted Action on the Methodology of Economic Appraisal of Health Technology.
References 1. Buxton 2. 3. 4. 5. 6. 7. 8‘ 9. 10. 11. 12. 13. 14.
MJ et al. Resource Management: Progress in the Pilot Sites. London: Department of Health 1989. Daschner F. Cost-effectiveness in hospital infection control-lessons for the 1990s. J Hosp Infect 1989; 13: 325-336. Drummond MF, Stoddart GL, Torrance GW. Methods for the Economic Evaluation of Health Care Programmes. Oxford: Oxford University Press 1987. Shapiro M, Schoenbaum SC, Tager IB et al. Cost benefit analysis of anti-microbial prophylaxis in abdominal and vaginal hysterectomy. JAMA 1983; 249: 1290-1294. Torrance GW, Zipursky A. Cost-effectiveness of antepartum prevention of RH immunization. Clin Perinatol 1984; 11: 267-281. Williams A. Economics of coronary bypass grafting. Br MedJ# 1985; 291: 326-329. Currie E, Maynard A. The economics of hospital acquired infection. Discussion Paper 56. University of York, Centre for Health Economics and Health Economics Consortium, 1989. Weinstein MC, Leighton Read J, Mackay DN et al. Cost-effective choice of antimicrobial therapy for serious infections. J Gen Intern Med 1986; 1: 352-363. Platt R, Polk BE, Murdock B et al. Prevention of catheter-associated urinary tract infection: a cost benefit analysis. Infect Control Hasp Epidemiol 1989; 10: 6&64. Persson U, Montgomery F, Carlsson A et al. How far does prophylaxis against infection in total joint replacement offset its cost? Br MedJ 1988; 296: 99-102. Atherley G, Cale RW, Drummond MF et al. An approach to the financial evaluation of occupational health services. r Sot Occup Med 1976; 26: 21-30. Mugford M, Kingston J, Chalmers I. Reducing the incidence of infection after caesarian section: implications of prophylaxis with antibiotics for hospital resources. Br Med J 1989; 299: 1000-1006. O’Leary MP. Economic considerations in management of complicated urinary tract infections. Urology (Suppl. 1) 1990; 35: 22-24. Haley RW, Schaberg DR, Von Allman SD et al. Estimating the extra charges and prolongation of hospitalization due to nosocomial infections: a comparison of methods. r Infect Dis 1980; 141: 248-257.
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15. Drummond MF, Stoddart GL. Economic analysis and clinical trials. Con Clin Trials 1984; 5: 115-128. 16. Drummond MF, Davies LM. Economic analysis alongside clinical trials: revisiting the methodological issues. Paper presented at the Joint Meeting of the European Health Economics Societies, Barcelona, 21-23 September 1989. 17. Hubner J, Frank U, Kappstein I et al. Influence of architectural design on nosocomial infections in intensive care units-a prospective 2-year analysis. Intensive Care Med (in press). 18. Department of Health. Working for Patients. London: Department of Health. 19. Schiefe RT, Cox CE, McCabe RE et al. Norfloxacin versus best parenteral therapy in treatment of moderate to serious multiply-resistant, nosocomial urinary tract infections: a pharmacoeconomic analysis. Urology 1988; 32 (Suppl. 3): 2430.