mrsa on tourniquets and keyboards

3
a sensitivity of 97.7%, a specificity of 99%, a posi- tive predictive value of 97.1% and a negative pre- dictive value of 99.5%. The two broths identified similar numbers of meticillin-susceptible S. aureus (328 vs 331/2033) but, as expected, only five strains were isolated from the agar plates. MRSA susceptibility to teicoplanin was estimated using E-test in 643 isolates from 169 patients. Six hundred and twenty-two isolates were susceptible by both standard and modified tests. Seven isolates had minimum inhibitory concentrations above the breakpoint by both tests, and 14 isolates were susceptible by the standard test but resistant by the modified test. Comparing the standard and modified tests, the sensitivity was 33% and the specificity was 100% (positive predictive value 100%, negative predictive value 97.8%). The concentration of salt did not affect S. aureus isolation rates in this study. Despite many screening media combinations being available, it is difficult to select one that is clearly superior to the rest. 3 Com- parative studies often use laboratory isolates rather than freshly collected specimens with a mixed bacterial flora. Pre-enrichment in salt- containing broth (6.5%) before plating on solid media has been shown to increase yields. 3 How- ever, a 2.5% salt concentration in aztreonam broth has been reported to be more sensitive in detecting MRSA than mannitol salt agar. 6 Mannitol agar with 7% salt may have a higher sensitivity than reduced salt formulations, but some find that more MRSA are inhibited at 7% salt broth than at 2.5%. 4,7 This study confirms earlier findings that the heavy inoc- ulum test has higher sensitivity and specificity in detecting GISA than a 0.5 McFarland method. 5 E-test has a similar performance to agar incorpora- tion and is superior to VITEK and disc testing. 8 Until the costs of molecular screening methods become more affordable, a balance has to be sought between speed of results and false- negative results. A plate method is adequate for critical care when a result is needed quickly to prevent cross-infection. When the detection of GISA is clinically important, e.g. bacteraemia in an intensive care unit, the heavy inoculum E-test should be used. References 1. Cepeda JA, Whitehouse T, Cooper B, et al. Isolation of patients in single rooms or cohorts to reduce spread of MRSA in intensive-care units: prospective two-centre study. Lancet 2005;365:295e304. 2. Cepeda J, Hayman S, Whitehouse T, et al. Teicoplanin resistance in methicillin-resistant Staphylococcus aureus in an intensive care unit. J Antimicrob Chemother 2003;52:533e534. 3. Safdar N, Narans L, Gordon B, Maki DG. Comparison of culture screening methods for detection of nasal carriage of methicillin-resistant Staphylococcus aureus: a prospective study comparing 32 methods. J Clin Microbiol 2003;41: 3163e3166. 4. Jones EM, Bowker KE, Cooke R, Marshall RJ, Reeves DS, MacGowan AP. Salt tolerance of EMRSA-16 and its effect on the sensitivity of screening cultures. J Hosp Infect 1997;35:59e62. 5. Walsh TR, Bolmstrom A, Qwarnstrom A, et al. Evaluation of current methods for detection of staphylococci with reduced susceptibility to glycopeptides. J Clin Microbiol 2001;39: 2439e2444. 6. Gurran C, Holliday MG, Perry JD, Ford M, Morgan S, Orr KE. A novel selective medium for the detection of methicillin- resistant Staphylococcus aureus enabling result reporting in under 24 h. J Hosp Infect 2002;52:148e151. 7. Zadik PM, Davies S, Whittaker S, Mason C. Evaluation of a new selective medium for methicillin-resistant Staphyloc- cocus aureus. J Med Microbiol 2001;50:476e479. 8. Charlesworth R, Warner M, Livermore DM, Wilson APR. Com- parison of four methods for detection of teicoplanin resistance in methicillin-resistant Staphylococcus aureus. J Antimicrob Chemother; in press. A.P.R. Wilson a, * S. Hayman a J.A. Cepeda a M. Singer b G. Bellingan b a Department of Clinical Microbiology, University College London Hospitals, London, UK b Bloomsbury Institute of Intensive Care Medicine, Department of Medicine, University College London, London, UK E-mail address: [email protected] Available online 3 July 2006 * Corresponding author. Address: Department of Clinical Microbiology, University College London Hospitals, 46 Cleveland Street, London W1T 4JF, UK. Tel.: þ44 207 380 9516; fax: þ44 207 636 6482. ª 2006 The Hospital Infection Society. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.jhin.2006.05.003 MRSA on tourniquets and keyboards Madam, Several studies have examined bacterial contami- nation rates on items in hospital wards, reporting bacterial prevalences of meticillin-resistant 86 Letters to the Editor

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Page 1: MRSA on tourniquets and keyboards

a sensitivity of 97.7%, a specificity of 99%, a posi-tive predictive value of 97.1% and a negative pre-dictive value of 99.5%. The two broths identifiedsimilar numbers of meticillin-susceptible S. aureus(328 vs 331/2033) but, as expected, only fivestrains were isolated from the agar plates.

MRSA susceptibility to teicoplanin was estimatedusing E-test in 643 isolates from 169 patients. Sixhundred and twenty-two isolates were susceptibleby both standard and modified tests. Seven isolateshad minimum inhibitory concentrations above thebreakpoint by both tests, and 14 isolates weresusceptible by the standard test but resistant bythe modified test. Comparing the standard andmodified tests, the sensitivity was 33% and thespecificity was 100% (positive predictive value100%, negative predictive value 97.8%).

The concentration of salt did not affect S. aureusisolation rates in this study. Despite many screeningmedia combinations being available, it is difficult toselect one that is clearly superior to the rest.3 Com-parative studies often use laboratory isolatesrather than freshly collected specimens witha mixed bacterial flora. Pre-enrichment in salt-containing broth (6.5%) before plating on solidmedia has been shown to increase yields.3 How-ever, a 2.5% salt concentration in aztreonam brothhas been reported to be more sensitive in detectingMRSA than mannitol salt agar.6 Mannitol agar with7% salt may have a higher sensitivity than reducedsalt formulations, but some find that more MRSAare inhibited at 7% salt broth than at 2.5%.4,7 Thisstudy confirms earlier findings that the heavy inoc-ulum test has higher sensitivity and specificity indetecting GISA than a 0.5 McFarland method.5

E-test has a similar performance to agar incorpora-tion and is superior to VITEK and disc testing.8

Until the costs of molecular screening methodsbecome more affordable, a balance has tobe sought between speed of results and false-negative results. A plate method is adequate forcritical care when a result is needed quickly toprevent cross-infection. When the detection ofGISA is clinically important, e.g. bacteraemia in anintensive care unit, the heavy inoculum E-testshould be used.

References

1. Cepeda JA, Whitehouse T, Cooper B, et al. Isolation ofpatients in single rooms or cohorts to reduce spread of MRSAin intensive-care units: prospective two-centre study. Lancet2005;365:295e304.

2. Cepeda J, Hayman S, Whitehouse T, et al. Teicoplanin resistancein methicillin-resistant Staphylococcus aureus in an intensivecare unit. J Antimicrob Chemother 2003;52:533e534.

3. Safdar N, Narans L, Gordon B, Maki DG. Comparison ofculture screening methods for detection of nasal carriageof methicillin-resistant Staphylococcus aureus: a prospectivestudy comparing 32 methods. J Clin Microbiol 2003;41:3163e3166.

4. Jones EM, Bowker KE, Cooke R, Marshall RJ, Reeves DS,MacGowan AP. Salt tolerance of EMRSA-16 and its effect on thesensitivity of screening cultures. J Hosp Infect 1997;35:59e62.

5. Walsh TR, Bolmstrom A, Qwarnstrom A, et al. Evaluation ofcurrent methods for detection of staphylococci with reducedsusceptibility to glycopeptides. J Clin Microbiol 2001;39:2439e2444.

6. Gurran C, Holliday MG, Perry JD, Ford M, Morgan S, Orr KE. Anovel selective medium for the detection of methicillin-resistant Staphylococcus aureus enabling result reporting inunder 24 h. J Hosp Infect 2002;52:148e151.

7. Zadik PM, Davies S, Whittaker S, Mason C. Evaluation ofa new selective medium for methicillin-resistant Staphyloc-cocus aureus. J Med Microbiol 2001;50:476e479.

8. Charlesworth R, Warner M, Livermore DM, Wilson APR. Com-parisonof fourmethods for detectionof teicoplanin resistancein methicillin-resistant Staphylococcus aureus. J AntimicrobChemother; in press.

A.P.R. Wilsona,*S. Haymana

J.A. Cepedaa

M. Singerb

G. Bellinganb

aDepartment of Clinical Microbiology, UniversityCollege London Hospitals, London, UK

bBloomsbury Institute of Intensive Care Medicine,Department of Medicine, University College

London, London, UKE-mail address: [email protected]

Available online 3 July 2006

* Corresponding author. Address: Department of ClinicalMicrobiology, University College London Hospitals, 46 ClevelandStreet, London W1T 4JF, UK. Tel.: þ44 207 380 9516; fax: þ44207 636 6482.

ª 2006 The Hospital Infection Society. Published by ElsevierLtd. All rights reserved.

doi:10.1016/j.jhin.2006.05.003

86 Letters to the Editor

MRSA on tourniquets and keyboards

Madam,

Several studies have examined bacterial contami-nation rates on items in hospital wards, reportingbacterial prevalences of meticillin-resistant

Page 2: MRSA on tourniquets and keyboards

Letters to the Editor 87

Staphylococcus aureus (MRSA) ranging from 0% toas much as 25e26% in selected environments,such as an MRSA outbreak or in intensive care units(ICUs).1e4

Most studies of bacterial contamination of com-puter keyboards have only examined keyboards inICUs rather than general wards, with one studydemonstrating that 49% of bacterial isolates wereMRSA.1,5 Re-usable tourniquets are also used fre-quentlyby largenumbersofhealthcareprofessionals;however, only one study has demonstrated the pres-ence of MRSA (reporting a prevalence of 29%)6 andtwo studies have found no MRSA.2,7 Despite not beingable to detect MRSA, Golder et al.7 identified otherpotential bacterial pathogens, including meticillin-sensitive S. aureus (MSSA) and Gram-negative bacilli,on 34% of tourniquets, and Rourke et al.2 identifiedMSSA on 5% of sampled tourniquets.

We undertook a study of the prevalence of MRSAon keyboards in general clinical areas and ontourniquets in frequent clinical use in a centralLondon teaching hospital.

Forty-four keyboards were sampled, using theenter key and the spacebar. Subsequently, Colom-bia blood agar (Oxoid, Basingstoke, UK) and ORSAplates (Oxoid) were inoculated with each swaband incubated at 37 �C in CO2 for 48 h for colonyidentification.

Fifty-two re-usable tourniquets were obtainedfrom 27 doctors from various specialities, 13 phle-botomists and 12 nurses. The donating healthcareprofessionals also completed a questionnaire abouttheir tourniquet usage.

Both surfaces of each tourniquet were pressedseparatelyon tonutrientagar (Oxoid)andORSAplates(half of each plate being used for each side of thetourniquet). In each case, a 5-cm length, 5 cm fromthe tourniquet buckle, was examined. Subsequently,the tourniquets were agitated in 10 mL of sterile waterfor 1 min, and 0.1 mL (one drop) of the solution wasthen transferred to nutrient agar and ORSA plates.Bacterial colony purification and subculture identi-fication were performed. MRSA isolates were sent tothe Laboratory of Healthcare Associated InfectionCentre for Infections for phage typing.

MSSA was found on nine of the 44 keyboardssampled, and four keyboards were positive for MRSA;three of phage type Epidemic (E-MRSA)-15 and oneof phage type Epidemic (E-MRSA)-16. MSSA wasidentified from 30 tourniquets and MRSA wasidentified on three (phage types 15 and 16).

Donors estimated the age range of the tourni-quets to be from two to 104 weeks, with the meanfor doctors being 11 weeks, nurses 93 weeks, andphlebotomists 32 weeks. Tourniquet usage alsovaried greatly with a mean daily usage of 11 times

(range 1e30). Interestingly, while all the healthcareprofessionals believed that re-using tourniquetsposed an infection risk, only 35.5% had ever cleanedthem, and 54.8% said that they refrained from usingtheir tourniquet on known infectious patients.

Our data add to the evidence that re-usabletourniquets and keyboards in general wards couldact as fomites for MSSA and MRSA. In agreementwith other tourniquet studies,2,6,7 we identifiedMSSA and, like Berman et al.,6 we were also ableto isolate MRSA, although at a lower prevalence.A possible explanation for the higher prevalencesof MRSA and MSSA reported here compared withmost other studies may be that our tourniquetswere pressed on to culture medium and agitatedin water rather than being subjected to impressionplating alone as used by Golder et al.7 and Rourkeet al.2 (Berman et al.’s6 method was not specified).

The isolation of MSSA and MRSA from bothtourniquets and keyboards in general clinical areasis of uncertain significance. It is recognized that thehospital environment can become contaminatedwith pathogens from infected patients, but therole that this may have in subsequent infection isdifficult to establish.8 However, the presence ofMSSA and MRSA on keyboards and tourniquets couldlead tohealthcare professionals re-inoculating theirhands even after washing, thus allowing the trans-mission of S. aureus to patients or other surfaces.

On the basis of our findings, we suggest thateasily cleanable keyboards or transparent plasticcovers may aid the fight against nosocomial in-fections. Likewise, tourniquets should either becleaned regularly or disposable alternatives shouldbe made available.

References

1. Bures S, Fishbain JT, Uyehara CF, Parker JM, Berg BW. Com-puter keyboards and faucet handles as reservoirs of nosoco-mial pathogens in the intensive care unit. Am J InfectControl 2000;28:465e471.

2. Rourke C, Bates C, Read RC. Poor hospital infection controlpractice in venepuncture and use of tourniquets. J HospInfect 2001;49:59e61.

3. Guinto CH, Bottone EJ, Raffalli JT, Montecalvo MA,Wormser GP. Evaluation of dedicated stethoscopes as apotential source of nosocomial pathogens. Am J InfectControl 2002;30:499e502.

4. French G, Rayner D, Branson M, Walsh M. Contamination ofdoctors’ and nurses’ pens with nosocomial pathogens. Lancet1998;351:213.

5. Hartmann B, Benson M, Junger A, et al. Computer keyboardand mouse as a reservoir of pathogens in an intensive careunit. J Clin Monit Comput 2004;18:7e12.

6. Berman DS, Schaefler S, Simberkoff MS, Rahal JJ. Tourni-quets and nosocomial methicillin-resistant Staphylococcusaureus infections. N Engl J Med 1986;315:514e515.

Page 3: MRSA on tourniquets and keyboards

immersion, making it difficult to tell the differencebetween the letters. However, this problem couldbe solved easily and keyboards are cheap. Whenthey are worn out, they could simply be replaced. Ihave not yet tried this on a cordless keyboard.

Reference

1. Wilson APR, Hayman S, Folan P, et al. Computer keyboardsand the spread of MRSA. J Hosp Infect 2006;62:390e392.

N. SimmonsE-mail address: [email protected]

Available online 10 July 2006

ª 2006 The Hospital Infection Society. Published by ElsevierLtd. All rights reserved.

doi:10.1016/j.jhin.2006.05.002

88 Letters to the Editor

7. Golder M, Chan CL, O’Shea S, Corbett K, Chrystie IL, French G.Potential risk of cross-infection during peripheral-venousaccess by contamination of tourniquets. Lancet 2000;355:44.

8. Barg NL. Environmental contamination with Staphlococcusaureus and outbreaks: the cause or the effect? Infect ControlHosp Epidemiol 1993;14:367e368.

C. Fellowes*R. Kerstein

J. ClarkB.S. Azadian

Chelsea and Westminster Hospital, London, UKE-mail address: [email protected]

Available online 7 July 2006

* Corresponding author. Tel.: þ44 208 846 7259; fax: þ44 208846 7260.

ª 2006 The Hospital Infection Society. Published by ElsevierLtd. All rights reserved.

doi:10.1016/j.jhin.2006.04.018

Computer keyboards and the spread of MRSA

Madam,

Recent correspondence from Wilson et al. re-garding computer keyboards and their place inthe spread of meticillin-resistant Staphylococcusaureus has prompted me to write this letter.1

About 1 year ago, my computer keyboard stoppedworking properly; the contacts inside were obvi-ously dirty. My information technology adviser toldme to put it through my dishwasher at home andallow it to dry out before reconnection. I did assuggested, and dried the keyboard out on top of theboiler. Afterwards, the keyboard worked perfectly.Furthermore, as the water had been close to 70 �Cfor several minutes, most, if not all, of the vegeta-tive bacteria on the keys would have been killed.

Keyboards are made of plastic, rubber and metalcontacts. Once they have been disconnected fromcomputers, they are not electrically charged. Con-sequently, they can then be immersed in hot waterand, if allowed to dry out thoroughly, can be usedagain. Could this not be used as a simple andeffective method of disinfection?

The only problem I can see is that the labels onthe keys may be washed off with repeated

Virus diffusion in isolation rooms

Madam,

We note that Kao and Yang’s numerical analysisconfirms the generally held opinion that isolationrooms should be negatively pressurized, witha piston ventilation system that promotes horizon-tal air flow over the patient and away from anyhealthcare workers (HCWs) present in the room.1

We also note, with interest, that by off-settingthe extract grilles behind the patient, it appearsto be possible to concentrate any infectious parti-cles produced to one side of the bed, thus leavingthe other side relatively free of contamination.This finding may be of some importance becauseit would enable a ‘safe zone’ (or, perhaps morecorrectly, a safer zone) to be created close tothe patient. The creation of such a zone wouldbe a significant advance because it would enablenurses and doctors to attend to the patient’s needsin relative safety, provided that they stayed withinthis area. Perhaps the area of the safe zone couldbe marked out on the floor?

In order to create a truly safe zone to the side ofthe patient, it would be necessary to ensure thatlarge respiratory droplets (>50 mm) are removed aswell as smaller droplet nuclei (<10 mm). Theselarger droplets, which may contain infectiousvirus, tend to fall to the ground within 1e2 mof the patient, whereas the smaller droplets