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Effect of Patient Movement between Wards on the acquisition of MRSA

Effect of Patient Movement between Wards on the acquisition of MRSA. Chris Robertson, Wenwen Huo Jacqui Reilly, David Greenhalgh University of Strathclyde and Health Protection S cotland. Objective.

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Effect of Patient Movement between Wards on the acquisition of MRSA

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  1. Effect of Patient Movement between Wards on the acquisition of MRSA Chris Robertson, WenwenHuo Jacqui Reilly, David Greenhalgh University of Strathclyde and Health Protection Scotland SIRN - November 2014

  2. Objective • Assess the role of patient movement between wards in hospital on the propensity of patients to acquire MRSA in hospital. • Patient movement was assessed in a number of ways • through the number of wards a patient was in during his or her stay in hospital • through measures designed to evaluate if a patient was in a ward at the same time as other patients who had MRSA SIRN - November 2014

  3. Data • MRSA Pathfinder Study which was designed as a multicentre cohort study within hospitals in two NHS Boards • Ayr & Arran and Grampian. • 600 and 900 beds respectively • Patients were screened for MRSA at multiple body sites on admission and at discharge. • February to August, 2010 • Tried to recruit all patients • Three cohorts depending upon consent • Admission Only Cohort – 7617 patients • Discharge Only Cohort – 2431 patients • Admission – Discharge Cohort – 2724 patients A Smith, PrChristie, T Stari, K Kavanagh, C Robertson, J Reilly, I Gould, F MacKenzie, R Masterton: Health Protection Scotland, National Services Scotland, NHS Scotland MRSA Screening; The Value of Nasal Swabbing versus Full Body Screening or Clinical Risk Assessment to Detect MRSA Colonisation at Admission to Hospital, 2011, Health Protection Scotland [Report] SIRN - November 2014

  4. Previous Analyses • In the sub-cohort of patients who were screened both on admission and on discharge and negative for MRSA on admission, 34 patients acquired MRSA while in hospital. • In the initial analysis of the admission discharge cohort, three risk factors for acquisition of MRSA were identified: • age group, • self-reported renal failure, and • self-reported presence of open wounds. E.V.H.V. Velzen, J.S. Reilly, K. Kavanagh, A. Leanord, G.F.S. Edwards, E.K. Girvan, I.M. Gould, F.M. MacKenzie, and R. Masterton. A retrospective cohort study into acquisition of MRSA and associated risk factors after implementation of universal screening in Scottish hospitals. Infect Control HospEpidemiol, 32(9):889-896, 2011 SIRN - November 2014

  5. Part 1: Descriptive analysis of effect of number of wards • Based upon Admission Discharge Cohort • Includes detailed investigation of the effect of length of stay and number of wards a patients was in • Logistic regression • Cochran-Mantel-Haenzel Stratified analysis • MRSA Acquisition – MRSA negative on admission and positive on discharge SIRN - November 2014

  6. Distribution of the number of wards a patient was in 87% of patients in 1 or 2 wards 57% only in 1 ward SIRN - November 2014

  7. Effect of the number of wards on MRSA acquisition Trend test , p = 0.039 SIRN - November 2014

  8. Confounding - Relationship between Age and number of wards SIRN - November 2014

  9. Length of stay and number of wards SIRN - November 2014

  10. Adjusted odds ratios Years Days Number of wards is not significantly associated with the risk of acquiring MRSA given that both older age and longer length of stay are associated with an increased risk of acquisition An extra day in hospital has the same effect as an extra year of age The magnitude of the effect of wounds/ulcers is about the same as 20 years of age SIRN - November 2014

  11. Adjusted odds ratios Final parsimonious model An extra 1.5 days in hospital has the same effect as an extra year of age The magnitude of the effect of wounds/ulcers is about the same as 20 years of age SIRN - November 2014

  12. Comparison with previous prediction model • The prediction model based upon the linear effect of age, linear effect of length of stay and the dichotomous effect of wounds/ulcers had an area under the curve (AUC) of 0.81 • Compared to AUC=0.79 from the original categorical model based upon age group, wounds/ulcers and renal failure (yes/no). • This difference was not statistically significant, p = 0.20, and both models have equal predictive power SIRN - November 2014

  13. ROC Sensitivity 80%, Specificity 55% Sensitivity 20%, Specificity 95% Sensitivity 85%, Specificity 70% Sensitivity 38%, Specificity 95% SIRN - November 2014

  14. Summary of effect of number of wards • The number of wards a patient stayed in during his/her hospital stay was positively associated with the risk of having MRSA on discharge. • However, adjusting for age and length of hospital stay there was no significant effect of number of wards. • The effect of the number of wards was confounded with the effect of age and with the effect of length of stay. • Older patients tended to be in more wards than younger patients and the longer the length of stay the greater the number of wards. • Within the admission discharge cohort it was not possible to disentangle the effect of the number of wards from the effects of length of stay. SIRN - November 2014

  15. Part 2: Patient Trajectory • Data from the admission only cohort, the discharge only cohort and the admission discharge cohort were pooled and used to map the trajectory of a patient through the hospital. • This could only be carried out in the main hospital in one NHS board as the availability of data on patient movement was much better there. • Even then there was missing data on • the dates of transfer from one ward to another and on • the dates of discharge, for the admission only cohort, and • dates of admission, for the discharge only cohort. SIRN - November 2014

  16. Ideal data to study patient movement SIRN - November 2014

  17. Occupancy and MRSA status by ward and by day Number of patients in each ward on each day Number of MRSA positive patients in each ward on each day SIRN - November 2014

  18. Exposure Variables • Exposed to MRSA • In the same ward at the same time as an MRSA patient • Days Exposed to MRSA • Total number of days in the same ward at the same time as an MRSA patient • Patient Days Exposed to MRSA • Total number of days in the same ward at the same time as an MRSA patient taking into account the number of MRSA patients in the ward • (2 MRSA patients 2 patient days exposure) SIRN - November 2014

  19. Exposure from Ideal data SIRN - November 2014

  20. Data Availability • In one hospital a great deal of missing data on patient movement • hospital omitted from patient trajectory analysis • In other hospital number of wards and sequence of wards was known but not dates of transfer SIRN - November 2014

  21. Available Data – One hospital only SIRN - November 2014

  22. Two strategies • Link data back to SMR01 to get dates of admission and discharge for the discharge only and admission only cohorts • This would not solve all the missing data issues • Also other problems associated with mismatches • Statistical modelling – imputation to estimate the missing data SIRN - November 2014

  23. Imputation • Statistical modelling and multiple imputation techniques were used • To estimate the number of days a patient was in a specific ward • to evaluate if any patient was exposed to MRSA in the same ward. • Admission discharge cohort used for modelling • Imputation in admission only and discharge only cohorts SIRN - November 2014

  24. Comparison of imputed length of stay with observed Blue – imputed Pink – observed Purple – overlap Imputation has too many in for 1 day Too few in for 2-5 days Imputation is not perfect but captures the general pattern SIRN - November 2014

  25. MRSA patients in a hospital per ward per day Number of MRSA patients in a ward Black (1) Red (2) Green (3) Blue (4) Yellow (5) Day from first admission in the discharge only cohort SIRN - November 2014

  26. In the same ward as a patient with MRSA Results from the admission discharge cohort in one hospital who were negative for MRSA on admission. Imputation only affected the exposure variable not the response – acquisition of MRSA. Imputation carried out 100 times and the results are the averages. SIRN - November 2014

  27. Bootstrap Adjusted Odds Ratios Adjusting for age, length of stay, open wounds/ulcers, renal failure SIRN - November 2014

  28. Patient Trajectory Summary • 17% of patients, on average, are exposed to an MRSA patient concurrently in the same ward during their hospital stay, • 83%, on average, are not exposed in this way. • The majority of patients who had possibly been exposed to MRSA did not acquire MRSA while in hospital. • On average, only 26% of the patients who acquired MRSA were concurrently in a ward with an MRSA patient while 74% of patients, on average, who acquired MRSA were not in a ward with another MRSA patient. • The effect of patient movement was not significantly associated with the risk of MRSA acquisition in hospital, after adjustment for age and length of stay or age, renal failure or wounds/ulcers. SIRN - November 2014

  29. Conclusions • This study indicated that cross-transmission of MRSA can take place in Scottish hospitals despite the implementation of Universal MRSA Screening. • However, concurrent exposure to MRSA in the same ward is not the only source of this cross transmission. • Other sources of transmission which include transmission from outside the ward or via hospital staff or environment are possibly important in the general hospital population. • Therefore, infection prevention, control measures and additional inventions for controlling MRSA in the hospital will be required. SIRN - November 2014

  30. Limitations • Lack of good quality data on patient movement between wards. • It was demonstrated that using imputation is feasible however the conclusions may not be robust. • The missing data means that there is the potential to underestimate the presence of MRSA in the wards. • More robust conclusions would be obtained using data from a hospital where • all patients were screened on admission and discharge and • dates of patient movement between wards and • date of discharge was recorded. SIRN - November 2014

  31. Limitations • Relatively low numbers of patients acquiring MRSA while in hospital. • Acquisition rates are low and so studies with a greater number of cases are required to assess the separate effects of number of wards, length of stay, and patient movement. SIRN - November 2014

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