Impact of mupirocin resistance on the transmission and control of healthcare-associated MRSA.
OBJECTIVE
The objectives of this study were to estimate the relative transmissibility of mupirocin-resistant (MupR) and mupirocin-susceptible (MupS) MRSA strains and evaluate the long-term impact of MupR on MRSA control policies.


METHODS
Parameters describing MupR and MupS strains were estimated using Markov chain Monte Carlo methods applied to data from two London teaching hospitals. These estimates parameterized a model used to evaluate the long-term impact of MupR on three mupirocin usage policies: 'clinical cases', 'screen and treat' and 'universal'. Strategies were assessed in terms of colonized and infected patient days and scenario and sensitivity analyses were performed.


RESULTS
The transmission probability of a MupS strain was 2.16 (95% CI 1.38-2.94) times that of a MupR strain in the absence of mupirocin usage. The total prevalence of MupR in colonized and infected MRSA patients after 5 years of simulation was 9.1% (95% CI 8.7%-9.6%) with the 'screen and treat' mupirocin policy, increasing to 21.3% (95% CI 20.9%-21.7%) with 'universal' mupirocin use. The prevalence of MupR increased in 50%-75% of simulations with 'universal' usage and >10% of simulations with 'screen and treat' usage in scenarios where MupS had a higher transmission probability than MupR.


CONCLUSIONS
Our results provide evidence from a clinical setting of a fitness cost associated with MupR in MRSA strains. This provides a plausible explanation for the low levels of mupirocin resistance seen following 'screen and treat' mupirocin usage. From our simulations, even under conservative estimates of relative transmissibility, we see long-term increases in the prevalence of MupR given 'universal' use.
Modelling and Economics Unit, Centre for Infectious Disease Surveillance and Control, Public Health England and Health Protection Research Unit in Modelling Methodology, London, UK sarah.deeny@phe.gov.uk.
Sarah R
SR
Deeny
Center for Communicable Disease Dynamics, Harvard School of Public Health, Boston, MA, USA.
Colin J
CJ
Worby
Centre for Clinical Infection and Diagnostics Research, Department of Infectious Diseases, King's College London, London, UK Guy's and St Thomas' NHS Foundation Trust, London, UK.
Olga
O
Tosas Auguet
Centre for Tropical Medicine and Global Health, Nuffield Department of Clinical Medicine, University of Oxford, Oxford, UK Mahidol-Oxford Tropical Medicine Research Unit, Bangkok, Thailand.
Ben S
BS
Cooper
Centre for Clinical Infection and Diagnostics Research, Department of Infectious Diseases, King's College London, London, UK Guy's and St Thomas' NHS Foundation Trust, London, UK.
Jonathan
J
Edgeworth
Division of Infection and Immunity, University College London, London, UK.
Barry
B
Cookson
Modelling and Economics Unit, Centre for Infectious Disease Surveillance and Control, Public Health England and Health Protection Research Unit in Modelling Methodology, London, UK.
Julie V
JV
Robotham
D000891:Anti-Infective Agents, Local / Q000494:pharmacology / Q000627:therapeutic use*; D002353:Carrier State / Q000188:drug therapy* / Q000517:prevention & control; D003428:Cross Infection / Q000188:drug therapy / Q000382:microbiology / Q000517:prevention & control / Q000635:transmission; D018562:Disease Transmission, Infectious / Q000517:prevention & control*; D024881:Drug Resistance, Bacterial; D006784:Hospitals, Teaching; D006801:Humans; D017053:Infection Control / Q000379:methods; D008131:London / Q000453:epidemiology; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects* / Q000302:isolation & purification; D015233:Models, Statistical; D016712:Mupirocin / Q000494:pharmacology / Q000627:therapeutic use*; D016134:Organizational Policy; D015995:Prevalence; D013203:Staphylococcal Infections / Q000188:drug therapy / Q000382:microbiology / Q000517:prevention & control* / Q000635:transmission
D000891:Anti-Infective Agents, Local; D016712:Mupirocin