variations in the frequency of mrsa infections across acute nhs hospitals, 2001-2006 paul fenn dev...

Variations in the frequency of MRSA infections across acute NHS hospitals, 2001-2006

Paul FennDev VencappaAlastair GrayOliver RiveroNeil Rickman

Background This study originated as part of research on the relationship

between liability risk-sharing measures and patient safety in the NHS [funded under the ESRC Public Services Programme]

Data on risk sharing measures available from the NHS Litigation Authority

Discounts available for risk management standards; hypothesis – financial incentives improve (or signal) patient safety measures, including hospital hygeine

MRSA surveillance data collected by Health Protection Agency since 2001 has progressively extended the panel of data that can be analysed alongside other DoH administrative datasets

Permits a wider set of hypotheses to be tested using panel data estimation methods in relation to the factors driving MRSA infection rates across hospitals and over time

Changes in length of stay, casemix and bed utilisation could plausibly affect the rate of hospital infections

Trends

Staphylococcus aureus bacteraemia reports (HPA, 2007)

MRSA bacteraemia reports from 2001 to 2006

01

23

45

67

89

10R

ate

per

10,0

00 F

CE

s

020

0040

0060

0080

00T

otal

MR

SA

rep

orts

2001 2002 2003 2004 2005 2006Year

Total MRSA reports Rate per 10,000 FCEs

MRSA infection rates by HC region from 2001 to 2006

46

810

46

810

46

810

2000 2002 2004 20062000 2002 2004 20062000 2002 2004 2006

East Midlands East of England London

North East North West South Central

South East South West West Midlands

MR

SA

infe

ctio

ns p

er 1

0,00

0 F

CE

s

YearGraphs by geo_local

Mean length of stay by HC region from 2001 to 2006

2.5

33.

54

2.5

33.

54

2.5

33.

54

2000 2002 2004 20062000 2002 2004 20062000 2002 2004 2006



South East South West West MidlandsMea

n le

ngth

of

stay


Mean bed utilisation rates by HC region from 2001 to 2006

.8.8

5.9

.8.8

5.9

.8.8

5.9

2000 2002 2004 20062000 2002 2004 20062000 2002 2004 2006




Mea

n be

d ut

ilisa

tion

rate


Distributions

Distributions of MRSA infections, NHS Acute Trusts

2001 2002 2003 2004 2005 2006 Total Nos.

0 3 3 2 4 4 3 19 1-10 21 17 22 20 19 18 117

11-20 24 29 19 23 20 30 145 21-30 29 23 32 31 33 35 183 31-40 29 33 24 18 25 22 151 41-50 13 15 14 18 13 16 89 51-60 9 10 15 13 16 14 77 61-70 6 5 8 11 10 11 51 71-80 7 9 2 6 8 7 39 81-90 5 5 7 6 2 4 29

91-100 9 5 6 7 7 4 38 101-110 2 5 6 5 5 4 27 111-120 2 2 1 1 3 1 10 121-130 2 2 4 3 0 0 11 131-140 0 0 3 0 1 0 4 141-150 2 2 0 0 1 0 5 151-160 1 1 0 1 0 0 3 161-170 1 2 1 0 1 0 5 171-180 0 0 0 0 0 1 1 181-190 1 1 1 0 0 0 3 191-200 1 0 0 1 0 0 2 201-210 0 0 1 0 0 0 1

Total 167 169 168 168 168 170 1,010 Source: MRSA Surveillance System, Department of Health

Distributions of MRSA infection rates by HC region

010

2030

010

2030

010

2030

0 10 20 30 0 10 20 30 0 10 20 30




Per

cent

MRSA infection rates/10,000 FCEsGraphs by geo_local

Drivers

Activity levels and casemix 2001-2006

2001 2002 2003 2004 2005 2006 Total

Finished consultant episodes 65098 70261 74359 76596 80573 83632 75246

Mean length of stay (days) 3.585 3.491 3.453 3.263 2.995 2.790 3.258

Bed utilisation rate 0.837 0.844 0.847 0.843 0.840 0.836 0.841

Proportion general medicine 0.219 0.238 0.252 0.248 0.247 0.235 0.240

Proportion general surgery 0.097 0.103 0.105 0.104 0.104 0.102 0.103

Proportion gynaecology 0.033 0.035 0.035 0.033 0.033 0.034 0.034

Proportion obstetrics 0.035 0.036 0.038 0.038 0.038 0.038 0.037

Proportion paediatrics 0.068 0.070 0.071 0.068 0.074 0.074 0.071

Proportion trauma/ orthopaedics 0.106 0.114 0.116 0.115 0.113 0.114 0.113

Proportion urology 0.020 0.022 0.022 0.022 0.021 0.021 0.021

Proportion other surgery 0.062 0.065 0.066 0.066 0.064 0.065 0.065

Proportion other medicine 0.257 0.282 0.280 0.290 0.289 0.304 0.284

Source: Hospital Episode Statistics by specialty, Department of Health

Direct measures to control MRSA, 2003-2007 2003: CMO provides specific directions on actions that

should be taken to reduce healthcare associated infections: better surveillance, improved techniques for use of catheters, tubes and

instruments, higher standards of hygiene in clinical practice, more prudent use of antibiotics, and a range of managerial and organisational changes

2004: “CleanYourHands” campaign launched by the NPSA 2004: DoH directs additional resources towards NHS trusts

with particularly high MRSA rates 2006: new Health Act introduced

detailed hygiene code for NHS organisations to assess and manage infection risks, implement clinical care protocols, and provide training

2007: “Deep Clean” initiative launched by DoH

CNST risk management standards, 2001-2006

Year Risk management standards Total 0 1 2 3 2001 20 117 26 1 164 2002 21 111 29 3 164 2003 7 115 39 5 166 2004 0 110 46 10 166 2005 0 88 68 10 166 2006 0 88 70 10 168

Total 48 629 278 39 982

CNST discount: 0% 10% 20% 30%

Source: NHS Litigation Authority

Standard 1 2 3 4 5

Criterion Governance

Competent &Capable

Workforce

SafeEnvironment

ClinicalCare

Learning fromExperience

1 Risk management strategy

Corporate induction Secure environment Patient identification Incident reporting

2 Policy on procedural documents

Local induction of permanent staff

Child protection Patient information Raising concerns

3 Risk management committee(s)

Local induction of temporary staff

Vulnerable adults Consent Complaints

4 Risk awareness training for senior management

Supervision of medical staff

in training

Moving & handling Clinical record-keeping standards

Claims

5 Risk management process

Risk management training

Slips, trips & falls Transfer of patients Investigations

6 Risk register Training needs analysis Inoculation incidents Medicines management

Analysis

7 Responding to external recommendations specific to the organisation

Medical devices training

Maintenance of medical devices & equipment

Blood transfusion Improvement

8 Clinical records management

Hand hygiene training Harassment & bullying Resuscitation Best practice - NICE, NCEs & national guidance

9 Professional clinical registration

Moving & handling training

Violence & aggression Infection control Best practice - NSFs & high level enquiries

10 Employment checks Supporting staff involved in an incident, complaint or claim

Stress Discharge of patients Being open

Source: NHSLA April 2007

Estimation

Estimating equation

= number of reported MRSA infections, hospital i, year titx

2ln( )itit it i it

it

xd u v

T 1βρ

= number of finished consultant episodes, hospital i, year titT

= vector of activity and casemix variables, hospital i, year titρ

= error term, hospital i, year titv

= vector of CNST risk management standards, hospital i, year titd

= unobserved effect, hospital iiu

Estimation Issues

Zero observations [xit = 0] Some hospitals omitted from analysis Solution: assume count data process

and estimate using QMLE or MLE

2ln( )itit it i it

it

xd u v

T 1βρ

Estimation Issues

Clustered sampling [it is not iid in pooled regression] Can lead to over-acceptance of

hypotheses relating to β1 and β2 Solution: use cluster-robust standard

errors

2ln( )itit it i it

it

xd u v

T 1βρ

Estimation Issues

Unobserved heterogeneity [ui ≠ 0] Omitted variable bias and/or inefficiency

if hospital effects unmodelled Solution: use panel data estimation

methods (random effects; fixed effects; first differencing)

2ln( )itit it i it

it

xd u v

T 1βρ

Estimation Issues

Endogeneity [E(ditvit) ≠ 0] Simultaneity bias Solution: use IV or GMM estimation

methods Internal instruments: lagged values of dit External instruments: claims experience of

hospital

2ln( )itit it i it

it

xd u v

T 1βρ

Results

(1) (2) (3) (4) (5) (6) Pooled

OLS RE GLS

FE OLS

Poisson QMLE

RE NB-ML

FE NB-ML

Ln(length of stay) 0.652*** 0.610*** 0.500** 0.884*** 0.769*** 0.476* (4.43) (5.29) (3.15) (5.52) (5.31) (2.20) Ln(bed utilization rate) -0.222 -0.122 -0.0754 -0.122 -0.0247 -0.0419 (-0.53) (-0.48) (-0.26) (-0.31) (-0.07) (-0.11) CNST level2 -0.0401 -0.0310 -0.0157 -0.0406 -0.0217 -0.0233 (-0.86) (-0.94) (-0.42) (-0.95) (-0.67) (-0.46) CNST level3 -0.206* -0.137 -0.0816 -0.160 -0.114 -0.00986 (-2.10) (-1.68) (-0.87) (-1.66) (-1.59) (-0.06) Proportion general surgery 0.233 0.926 3.196* 1.431 1.706 3.929* (0.18) (0.98) (2.18) (1.46) (1.88) (2.03) Proportion gynaecology -1.002 -1.193 -3.313* -1.658 -1.387 -2.223 (-1.34) (-1.70) (-2.10) (-1.77) (-1.93) (-1.00) Proportion obstetrics -1.088* -1.673** -3.938** -1.617* -2.488** -3.940* (-1.99) (-3.10) (-2.90) (-2.00) (-3.15) (-2.15) Proportion paediatrics -0.637 -0.696 -0.897 -0.582 -0.475 0.269 (-1.38) (-1.75) (-1.14) (-0.99) (-1.03) (0.17) Proportion trauma & orthopaedics -0.474 -0.575 0.896 -0.461 -0.707* 1.209 (-1.43) (-1.83) (0.70) (-1.23) (-2.23) (0.66) Proportion urology -0.904 -1.431 -1.325 -0.403 -1.244 -0.810 (-0.35) (-0.67) (-0.38) (-0.18) (-0.64) (-0.18) Proportion other surgery 1.375** 1.150*** 0.384 1.364*** 0.835* 0.187 (3.29) (3.56) (0.73) (3.34) (2.38) (0.27) Proportion other medicine 0.215 0.126 -0.0957 0.111 0.0863 -0.126 (0.98) (0.75) (-0.40) (0.56) (0.53) (-0.38) Proportion psychiatry -1.338 -1.603** -1.295* -1.319 -1.698** -0.969 (-1.85) (-2.84) (-2.00) (-1.92) (-3.11) (-1.08) Single specialty hospital -0.946*** -0.829*** -0.915*** -0.763*** (-4.37) (-5.84) (-4.73) (-4.32) Teaching hospital 0.205** 0.191** 0.211*** 0.212*** (3.05) (2.88) (3.40) (3.51)

Estimation with exogenous regressors

Note: Region and year dummies omitted

(1) (2) (3) (4) (5) Pooled

linear GMM

RE EC2SLS

FE linear GMM

Pooled nonlinear GMM

q-diff nonlinear GMM

Ln(length of stay) 0.653*** 0.620*** 0.506** 0.862*** 0.836*** (4.60) (5.41) (3.14) (5.52) (3.62) Ln(bed utilization rate) -0.212 -0.125 -0.0915 -0.118 0.5293 (-0.53) (-0.49) (-0.31) (-0.31) (1.20) CNST level2 -0.0114 -0.108 -0.107 -0.051 (-0.12) (-1.54) (-0.54) (-0.57) CNST level3 -0.290** -0.224 -0.212 -0.328*** -0.0523 (-3.17) (-1.49) (-0.41) (-4.21) (-0.81) Proportion general surgery -0.103 0.808 3.089* 1.211 -2.5777 (-0.08) (0.86) (2.08) (1.30) (-1.28) Proportion gynaecology -0.829 -0.984 -3.157 -1.661 -2.8448 (-1.16) (-1.39) (-1.86) (-1.80) (-1.32) Proportion obstetrics -1.206* -1.569** -4.013** -2.009* -3.166* (-2.31) (-2.91) (-2.92) (-2.51) (-1.99) Proportion paediatrics -0.692 -0.689 -0.826 -0.698 -1.0807 (-1.54) (-1.76) (-0.97) (-1.24) (-1.08) Proportion trauma & orthopaedics -0.569 -0.544 1.153 -0.689* -0.6474 (-1.73) (-1.76) (0.87) (-2.00) (-0.68) Proportion urology -0.884 -0.915 -0.594 0.416 -12.387 (-0.35) (-0.43) (-0.16) (0.20) (-1.89) Proportion other surgery 1.215** 1.169*** 0.460 1.001** 0.0501 (3.05) (3.68) (0.82) (2.67) (0.05) Proportion other medicine 0.172 0.151 -0.0539 -0.019 -0.3767 (0.86) (0.90) (-0.21) (-0.10) (-1.19) Proportion psychiatry -1.415 -1.635** -1.305* -1.381* -4.096** (-1.95) (-2.87) (-2.00) (-2.00) (-3.60) Single specialty hospital -0.928*** -0.831*** -0.801*** (-4.40) (-5.97) (-4.62) Teaching hospital 0.228*** 0.194** 0.235*** (3.49) (3.01) (4.06)

Estimation with endogenous regressors

Note: Region and year dummies omitted

Unexplained reduction in MRSA rate relative to 2001

-20.00%

-15.00%

-10.00%

-5.00%

0.00%

5.00%

2001 2002 2003 2004 2005 2006

Pooled OLS

RE GLS

FE OLS

Poisson QMLE

RE NB-ML

FE NB-ML

Pooled GMM

RE EC2SLS

FE GMM

Nonlinear GMM

Conclusions

Conclusions Average length of stay is the main driver behind changes in

MRSA infection rates over time Of the 27% fall in MRSA rates between 2001/2 and 2006/7,

somewhere between 11% (short-run) and 19% (long-run) is attributable to the overall fall in length of stay over this period

Because the other factors we explored are either insignificant or have changed little over the period, the remaining fall in the MRSA rate is “unexplained” and could potentially be attributable to measures such as the NPSA’s “CleanYourHands” campaign

Casemix and location are important factors explaining differences in MRSA rates across acute hospitals

Hospitals with a higher proportion of surgical admissions have higher MRSA rates; hospitals with a higher proportion of O&G, paediatric, and psychiatric admissions have lower MRSA rates.

Acute hospitals in London, the South-East and the West Midlands have significantly higher MRSA rates than in other regions, after controlling for other factors including casemix and length of stay

Conclusions Controlling for casemix, location and length of stay,

single-specialty acute hospitals have much lower MRSA rates than other acute hospitals

Controlling for casemix, location and length of stay, acute teaching hospitals have higher MRSA rates than other acute hospitals (although this differential has weakened considerably since 2003)

There is some (inconclusive) evidence that hospitals achieving the highest CNST risk management standard (level 3) have lower MRSA infection rates

There is no evidence that, after controlling for location, variations in bed utilisation rates across acute hospitals have a significant effect on their MRSA infection rates

variations in the frequency of mrsa infections across acute nhs hospitals, 2001-2006 paul fenn dev...

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