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Cost comparison of MRSA screening and management – a decision tree analysis
© Tuebbicke et al.; licensee BioMed Central Ltd. 2013
Received: 30 March 2012
Accepted: 20 November 2012
Published: 1 December 2012
Methicillin-resistant Staphylococcus aureus (MRSA) infections represent a serious challenge for health-care institutions. Rapid and precise identification of MRSA carriers can help to reduce both nosocomial transmissions and unnecessary isolations and associated costs. The practical details of MRSA screenings (who, how, when and where to screen) remain a controversial issue.
Aim of this study was to determine which MRSA screening and management strategy causes the lowest expected cost for a hospital. For this cost analysis a decision analytic cost model was developed, primary based on data from peer-reviewed literature. Single and multiplex sensitivity analyses of the parameters “costs per MRSA case per day”, “costs for pre-emptive isolation per day”, “MRSA rate of transmission not in isolation per day” and “MRSA prevalence” were conducted.
The omission of MRSA screening was identified as the alternative with the highest risk for the hospital. Universal MRSA screening strategies are by far more cost-intensive than targeted screening approaches. Culture confirmation of positive PCR results in combination with pre-emptive isolation generates the lowest costs for a hospital. This strategy minimizes the chance of false-positive results as well as the possibility of MRSA cross transmissions and therefore contains the costs for the hospital. These results were confirmed by multiplex and single sensitivity analyses. Single sensitivity analyses have shown that the parameters “MRSA prevalence” and the “rate of MRSA of transmission per day of non-isolated patients” exert the greatest influence on the choice of the favorite screening strategy.
It was shown that universal MRSA screening strategies are far more cost-intensive than the targeted screening approaches. In addition, it was demonstrated that all targeted screening strategies produce lower costs than not performing a screening at all.
Methicillin-resistant Staphylococcus aureus (MRSA) infections represent a serious challenge for health care institutions [1–3]. In order to assure rapid treatment of MRSA patients, a reduction of unnecessary isolation precautions and prevention of potential cross infections as well as rapid and precise identification of MRSA are required. Although the implementation of MRSA screening is associated with high expenses for the hospital, the cost-effectiveness of performing MRSA screening has already been confirmed in several studies [4–7]. However, MRSA screenings remains a controversial issue, as the identification of the strategy which causes the lowest expected cost for a hospital is still the object of inquiry.
Which patient groups should be included in the screening program? A mandatory universal screening program includes all inpatients being admitted to the hospital. Targeted screening is limited to high-risk patients or areas of the hospital. Among these high-risk admissions are old and multi morbid patients, patients with chronic diseases, open wounds, eczema, burns, and patients requiring dialysis. Further documented risk factors are long hospital stays, intravenous drug use, invasive lines or tubes such as catheters, and prior antibiotic exposure [8, 9]. The Robert Koch-Institute defines the following patient groups as high-risk patients: patients with nursing care dependency, dialysis patients, invasive lines or tubes such as catheters, patients with chronic wounds, burns, skin ulcers, gangrene soft tissue infection as well as patients with known MRSA anamnesis [8, 9]. In addition to the criteria named above, patients transferred from regions, hospitals and other medical institutions with a noted high MRSA prevalence, patients with a stay at another hospital during the last three months as well as patients working in animal breeding belong to the high-risk patient group. Furthermore certain areas of the hospital are declared as high-risk areas such as ICU, weaning ward, stroke unit and dermatological ward.
Which laboratory technique allows a rapid, precise and cost-effective diagnostic investigation? After swabs are taken from the patient, hospitals can settle for the polymerase chain reaction (PCR) method, which is a genotypic method to determine the methicillin-resistance of staphylococcus. Another option is the conventional culturing technique. Microorganisms are incubated on culture media and are differentiated phenotypically. Susceptibility to antimicrobials is determined afterwards by standardized methods. Hospitals can also decide for a combination of the two methods.
Another question that needs to be answered is how to deal with screened patients until the MRSA test result is available, that is, should screened patients be treated as MRSA carriers and put in isolation until MRSA is excluded or should no action be taken until MRSA has been confirmed?
Which swab site or rather a combination of swab sites offers high sensitivity? Nasal swabs are considered to be the minimum standard. Groin, axilla or wound swabs are also appropriate .
Is it reasonable to screen patients only upon hospital admission or to additionally conduct follow-ups and contact-patient screenings?
The aim of this study was a cost analysis to determine which MRSA screening and management strategy causes the lowest expected cost for a hospital. For this purpose, a decision tree was modelled and corresponding calculations were made. We conducted various sensitivity analyses in order to examine the stability of the results obtained.
Decision making problem and decision tree
If the MRSA-test is negative, pre-emptive isolation is immediately discontinued and no further steps are taken. In the present model, the decision tree branches end after MRSA is excluded or after MRSA eradication treatment and follow-up screening has been conducted. It is assumed that the culture method is applied for the follow-up screening as well as the contact-patient screening and that these test results turn out to be negative. Therefore, costs for a negative culture test are assessed in the calculations. With regard to MRSA prevalence, an interrelation between the parameters “MRSA prevalence inpatients” and “MRSA prevalence high-risk inpatients” is implied. The higher the prevalence among all inpatients, the higher will also be the prevalence among high-risk inpatients and vice versa. However, the exact ratio between the two parameters is unknown.
Systematic literature search
Definition and quantification of variables
MRSA prevalence of all inpatients
MRSA prevalence of high-risk inpatients
MRSA prevalence of patients without indication for a targeted screening
RT no iso
Rate of MRSA transmission not in isolation per day
Rate of MRSA transmission in isolation per day
Sensitivity of PCR method
Sensitivity of culture method
Specificity of PCR method
Specificity of culture method
Average costs for pre-emptive isolation per day
Average costs per MRSA case per day
∅ LOS MRSA
Average length of stay of MRSA patients in days
Definition and quantification of constants
turn-around time of PCR method in days
turn-around time of culture method in days
costs for a single PCR test
C cul pos
costs for a single culture test with positive result
C cul neg
costs for a single culture test with negative result
costs for follow-up screening
As follow-up screening in the majority of cases leads to a negative result, costs for negative culture tests are assessed
costs for screening a contact patient
As follow-up screening in the majority of cases leads to a negative result, costs for negative culture tests are assessed
number of contact patients
Calculation based on in-house data
∅ LOS reg
average length of stay of regular patients in days
Federal Statistical Office 
number of total inpatients per year
number of high-risk patients per year
number of patients without indication for a targeted screening per year
C MRSA ici
costs for MRSA caused by incomplete MRSA carrier identification
performance of PCR methods: 36
performance of culture methods: 30
MRSA transmission rates: 7
MRSA prevalence in German hospitals: 6
MRSA prevalence of high-risk inpatients or patients in high-risk areas in German hospitals: 3
costs per MRSA case: 11
costs for pre-emptive isolation per day: 5
As 9 of all 98 identified studies provide information for more than one parameter of interest, these studies were retrieved several times. Eventually, 87 different studies were identified by the search. Relevant data were abstracted from all these studies. Tables 1 and 2 provide an overview (minimum, maximum and average values of the retrieved data) of the concrete values and significances of the variables and constants obtained by the literature review.
Since not all parameters compiled in the Tables 1 and 2 could be quantified by systematic literature, assumptions had to be made. The costs for a PCR test as well as for positive and negative culture tests were estimated corresponding to the German uniform valuation standard (EBM) . Estimations of the turn-around times of both methods are based on in-house data. The number of contact patients was calculated by dividing the average occupied hospital beds by the number of patient rooms.
Congruent to the procedure shown above, the expected costs for each Strategy A- T are determined.
A multiplex sensitivity analysis was conducted by a simultaneous variation of more than one parameter. The following variables were varied in three steps from minimum to maximum of the existing data (Table 1): rate of MRSA transmission not in isolation per day, rate of MRSA transmission in isolation per day, costs for MRSA case per day, costs for pre-emptive isolation per day, MRSA prevalence inpatients, MRSA prevalence high-risk inpatients, sensitivity of PCR method, specificity of PCR method, sensitivity of culture method and specificity of culture method. Consequentially, 59,049 (= 310) different scenarios were generated.
Single sensitivity analyses aimed at determining the influence of a certain parameter on the expected costs of the screening strategies. The parameter in focus was therefore increased in ten steps from minimum to maximum of the existing data according to Table 1 while all other variables were kept at their average value.
The results show that an omission of an MRSA screening causes higher costs than performing a targeted screening. Only a universal screening approach is more costly than not to perform a screening at all.
Multiplex sensitivity analysis
Single sensitivity analysis
As expected, the increase of the parameter “costs per MRSA case per day” led to growing costs. Over the entire augmentation of this parameter strategies R and S (targeted PCR screening with culture confirmation in the case of a positive PCR result with and without pre-emptive isolation) proved to be the cost-minimizing screening strategies. These strategies showed almost equal outcomes. However, Strategy S was favourable at amounts up to 740 €, while Strategy R became advantageous when costs per MRSA case per day were higher.
The increase of the parameter “costs for pre-emptive isolation per day” resulted in an increase of costs for all strategies which include the conduction of pre-emptive isolation precautions, while the costs for all other alternatives remained constant. The Strategies R and S once again produced the lowest costs. Up to costs amounting to 44 €, Strategy R was the better choice. If the costs for pre-emptive isolation per day were higher than that, the decision-maker should choose Strategy S.
To the authors’ knowledge, this study is the first quantitative evaluation to determine which MRSA screening and management strategy causes the lowest expected cost for a hospital based on a decision-tree model. We succeeded in identifying who, how, when and where to screen patients for MRSA in order to minimize costs.
The results of the decision-tree analysis suggest that a universal screening approach cannot be expected to be cost-minimizing. All screening strategies pursuing a screening for all inpatients produce higher costs than not to perform a screening at all. This is congruent with the results of other studies, which state that screening all patients being admitted to the hospital is desirable in terms of a complete carrier identification, but this approach is neither affordable nor cost-reducing for hospitals [16, 17].
Furthermore, it was shown that all strategies performing a targeted screening produce lower costs in comparison to an omission of MRSA screening. For this reason, evidence for the advantageousness of conducting a targeted screening for all high-risk patients is provided by cost-analyses. This is consistent with results of other analyses [4–7, 18].
Choosing Strategy T, which means not performing a screening, implies the highest risk for the hospital. Under certain circumstances it can be advantageous, but oftentimes it is the most expensive alternative and on average considerably worse than pursuing a targeted screening approach. Risk-averse decision-makers would therefore tend not to choose this option.
The results show that the alternatives S and R produce the lowest expected costs among all screening strategies. Both strategies focus on PCR screening with culture confirmation in the case of a positive PCR result. The difference between the two options refers to pre-emptive isolation, which is performed by Strategy R and omitted by Strategy S. While both alternatives on average cause costs in similar amounts, the decision-maker should select Strategy R, because it is often the cheapest but never the most expensive. The advantage can be ascribed to the pre-emptive isolation precautions, which minimizes the risk of MRSA cross transmissions and at the same time contains the costs for the hospital. This increases in relevance when the rate of MRSA transmission not in isolation and MRSA prevalence turn out to be high. This approach is also supported by the literature. When a PCR result proves to be positive, the possibility remains that it is false-positive, because the validity of the PCR method is restricted in the case of a coincidental colonization with Staphylococcus aureus and coagulase-negative staphylococcus . Furthermore, the PCR method can lead to positive test results even when MRSA germs have been inactivated by a successful eradication therapy . For this reason, it is recommended to perform a culture confirmation, in order to exclude false-positive PCR results .
Our analysis has various limitations. First, a weakness can be seen in the quantification of the parameters included in the calculations. Our data were basically obtained by a systematic literature research , but in some cases, the data were insufficient and assumptions had to be made on the basis of in-house data and experience. The better the data are tailored to the particular hospital setting, the more significant are the results produced by the decision-tree analysis modelled for this study. In this context, a concrete limitation is evident in terms of the single sensitivity analysis of MRSA prevalence. It is known that there is an interdependence of the parameters “MRSA prevalence”, “MRSA prevalence high-risk inpatients” and “MRSA prevalence among patients without indication for a targeted screening”, but the exact ratio remains uncertain, which limits the validity of this single sensitivity analysis .
The results of our decision-tree analysis and the corresponding calculations still allow us to draw conclusions and give recommendations on how to perform an MRSA screening in the cost-minimizing way.
In summary, it was shown that universal MRSA screening strategies are far more cost-intensive than the targeted screening approaches. In addition, it was demonstrated that all targeted screening strategies produce lower costs than not performing a screening at all. The advantageousness of performing a targeted MRSA screening is therefore proven by the present analysis. The omission of an MRSA screening was identified as the alternative attended by the highest risk for a hospital. Among the targeted screening strategies, performing a PCR screening and culture confirmation in the case of a positive PCR result (strategies R and S) generates the lowest costs for a hospital. The decision-maker should select Strategy R, as pre-emptive isolation minimizes the chance of false-positive results as well as the possibility of MRSA cross transmissions, and at the same time contains the costs for the hospital. Therefore, it bears a lower risk in comparison to Strategy S, which does not take pre-emptive isolation precautions.
Further evidence, especially empiric data on costs and outcomes, would help to strengthen the model and support the hitherto largely theoretical statements.
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