Screening, isolation, and decolonisation strategies in the control of meticillin resistant Staphylococcus aureus in intensive care units: cost effectiveness evaluation

Abstract

Objective: To assess the cost effectiveness of screening, isolation, and decolonisation strategies in the control of meticillin resistant Staphylococcus aureus (MRSA) in intensive care units.

Design: Economic evaluation based on a dynamic transmission model.

Setting: England and Wales. Population Theoretical population of patients on an intensive care unit.

Main outcome measures: Infections, deaths, costs, quality adjusted life years (QALYs), incremental cost effectiveness ratios for alternative strategies, and net monetary benefits.

Results: All decolonisation strategies improved health outcomes and reduced costs. Although universal decolonisation (regardless of MRSA status) was the most cost effective in the short term, strategies using screening to target MRSA carriers may be preferred owing to the reduced risk of selecting for resistance. Among such targeted strategies, universal admission and weekly screening with polymerase chain reaction coupled with decolonisation using nasal mupirocin was the most cost effective. This finding was robust to the size of intensive care units, prevalence of MRSA on admission, proportion of patients classified as high risk, and precise value of willingness to pay for health benefits. All strategies using isolation but not decolonisation improved health outcomes but costs were increased. When the prevalence of MRSA on admission to the intensive care unit was 5% and the willingness to pay per QALY gained was between £20,000 (€23,000; $32,000) and £30,000, the best such strategy was to isolate only those patients at high risk of carrying MRSA (either pre-emptively or after identification by admission and weekly screening for MRSA using chromogenic agar). Universal admission and weekly screening using polymerase chain reaction based detection of MRSA coupled with isolation was unlikely to be cost effective unless prevalence was high (10% of patients colonised with MRSA on admission).

Conclusions: MRSA control strategies that use decolonisation are likely to be cost saving in an intensive care unit setting provided resistance is lacking, and combining universal screening using polymerase chain reaction with decolonisation is likely to represent good value for money if untargeted decolonisation is considered unacceptable. In intensive care units where decolonisation is not implemented, evidence is insufficient to support universal screening for MRSA outside high prevalence settings.

Fig 1 Model schematic showing possible movements of patients (dotted arrows) and transitions between states (solid arrows). MRSA=meticillin resistant Staphylococcus aureus

Fig 2 Cost effectiveness acceptability curves and frontiers for screening and decolonisation strategies. Each line on cost effectiveness acceptability curve represents the proportion of simulations for a particular strategy that are cost effective, under a range of values for willingness to pay for health benefits. Lines in cost effectiveness acceptability frontiers depict scenarios with highest expected net monetary benefit, dependent on willingness to pay for health benefits. The first frontier compares all strategies; the second excludes universal decolonisation

Fig 3 Use of isolation under each screening and isolation strategy, showing appropriate isolation (isolation of MRSA positive patients), inappropriate isolation (isolation of MRSA negative patients), and bed days spent unisolated while MRSA positive

Fig 4 Patient outcomes under each screening and isolation strategy, showing new acquisitions (transmissions) of MRSA by patients in an intensive care unit, total number of MRSA infections in an intensive care unit, and total number of deaths (all per 100 admissions)

Fig 5 Cost effectiveness acceptability curves and frontier for screening and isolation strategies. Lines in cost effectiveness acceptability frontier depict strategies with highest expected net monetary benefit dependent on willingness to pay for health benefits