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2380 LETTERS TO THE EDITOR

hominis (5), contrary to Dr. Rosenblatt's allegation, the authors appear to have performed normal laboratory tests, including routine aerobic and anaerobic cultures ofblood, synovial fluid, urine, stool, and endocervix (all negative). Had the authors includedaphotomicrographof theorganism as "scientific documentation" or "illustration," most refer-ees probably would have suggested deletion because the parasite is so well described and easy to identify. Dr. Rosenblattappears toquestiontheintegrityandcompetence of theinvestigators. Is it because of their affiliationwith an institutioninJamaica? Probablythey seemore parasites in a monththan acomparablysized hospital in the United States in1 year.

NeitherInorsome 20 other investigators, reportingover 500 cases of B. hominis-associated gastroenteritis, and 2 withopposing views (16 cases) have any vested interest in the organism or its pathogenicity. All have reported their observations and experiences in peer-reviewed journals. Editors and referees of scientific and medical periodicals judge manuscripts ontheirmerit, scientific documentation, and proper interpretation. Expecting them to be narrow-minded is defeating their purpose.

I concur with Dr. Rosenblatt and several previous in-vestigators that more information is needed regarding the epidemiology, mechanism of pathogenicity, immunologic response, radiologicand endoscopic findings, and manage-mentofB. hominisinfections andhopethatthecontroversy surrounding this parasite's role in disease will stimulate researchtoelucidate theseparameters.

LITERATURECITED

1. Babcock, D., R. Houston, D. Kumaki, and D. Shlim. 1986. Blastocystishominis in Kathmandu, Nepal. N. Engl. J. Med. 313:1419.

2. Cohen, A. N. 1985. Ketoconazole and resistant Blastocystis hominisinfection. Ann. Intern. Med. 103:480481.

3. Guirges,S.Y., andN.S.AI-Waili. 1987.Blastocystis hominis: evidence for human pathogenicity and effectiveness of metro-nidazole therapy. Clin. Exp. Pharmacol. Physiol. 14:333-335. 4. Kain, K. C., M. A. Noble, H. J. Freeman, and R. L. Barteluk.

1987.Epidemiology and clinicalfeaturesassociated with Blas-tocystishominisinfection. Diagn. Microbiol. Infect. Dis. 8:235-244.

5. Lee, M. G., S. C.Rawlins, M.Didier, and K. DeCeulaer. 1990. Infective arthritis due to Blastocystis hominis. Ann. Rheum. Dis. 48:192-193.

6. Phillipps, B. P., and C. H. Zierdt. 1976.Blastocystis hominis: pathogenicpotentialin humanpatients and in gnotobiotes. Exp. Parasitol. 39:358-364.

7. Qadri, S.M.H., G.A.Al-Okaili,andF.Al-Dayel.1989. Clinical significance of Blastocystis hominis. J. Clin. Microbiol. 27: 2407-2409.

8. Russo,A.R.,L.Stone,M.E.Taplin,H.J.Snapper,andG.V. Doern.1988. Presumptive evidence for Blastocystis hominis as acauseofcolitis. Arch. Intern. Med. 148:1064.

9. Sangiorgi, G. 1930. Pathogenicity of Blastocystis hominis. Pathologica 22:173-176.

10. Sheehan, D. J., B. G. Raucher, and J. C. McKitrick. 1986. Association of Blastocystis hominis with signs and symptomsof humandisease. J. Clin. Microbiol. 24:548-550.

11. Taylor,D.N.,R.Houston, D. R.Shlim, M.Bhaibulaya, U.L. Ungar, and P. Echeverria. 1988. Etiology of diarrhea among travellersandresidentsinNepal. J. Am. Med. Assoc. 260:1245-1248.

12. Yakimoff, W.L. 1923. Sur laquestion desBlastocystis. Bull. Soc. Pathol. Exot. Fil. 161:326.

13. Zierdt, C.H., C.T.Donnolley, J. Muller,andG. Constantopou-los.1988. Biochemical and ultrastructural study of Blastocystis hominis. J. Clin. Microbiol. 26:965-970.

S.M. HussainQadri

DepartmentofPathology and Laboratory Medicine KingFaisal Specialist Hospital and Research Centre P.O.Box3354

Riyadh 11211, SaudiArabia

Selective

Staphylococcal

Broth

We compliment Dr. Cookson et al. on their extremely

informative articleonstaffcarriage ofepidemic

methicillin-resistant Staphylococcus aureus (MRSA) (3). The authors

make an extremely pertinent statement: "we used broth enrichmentculturingtoincreasethesensitivity of detection of EMRSA [epidemic MRSA] carriage; in fact, without it carriage would have been entirely missed in eight of our

nurses." Theuseof this most sensitive culturemethod for thedetectionof MRSA inepidemiologicalsurveillance can-not be overemphasized. In a recent review of MRSA (1), eachof the epidemiological investigations cited used direct plating methods and showed that the carriageratefor MRSA

was low. It is our contention that the use of insensitive

culturemethods for MRSAinepidemiologicalsurveillance is

one possible reason for the low carriage rates for MRSA reported in the literature.

Inacomparison of plated media, includingBaird-Parker,

Trypticase soy with5% sheep blood (BAP), andchocolate

agarwith staphylococcalbroth, wehave been ableto dem-onstratetheisolationof almost three timesasmanypositive

S. aureus cultures as by any plated agar method (unpub-lished data). Recently, one ofus reported that a selective

staphylococcal broth (Difco Laboratories, Detroit, Mich.)

proved superior to direct plating for the recovery of S. aureus, resulting in

improved

recovery ratesof

20%

(nares)

and

66%

(vaginal vestibule) (4). Referring

to these

data,

Campos

(2)

suggested

the use of a broth enrichment for

detecting MRSA in surveillance cultures. We have also

compared

staphylococcal

broth with direct

plating

for the

recovery of MRSA on BAP. In an attempt to

identify

carriers of

epidemic MRSA,

124

intensive-care-unit

and 14

operating-room

employees

had cultures of the nares. Four

employees

(2.9%)

carried MRSA.

Ail

four MRSA isolates

were

found

in the

selective

brothcultures,whileonlytwoof

the four

(50%)

were detected by direct

plating.

MRSA could be detected only on repeat cultures of

specimens

from these four

employees

by the

selective

culture tech-nique.

Althoughthe useofanenrichment broth for culturesin the laboratory is routine, in

practice

most laboratories do not usebrothenrichment for

epidemiological

surveillance.The

factthat62%of

positive

individuals in theCookson

evalua-tionand50%in ourevaluation wouldnothavebeen

detected

without the use ofan enrichment broth culture

technique

strongly suggests the need to use this culture method for

epidemiological

surveillance.

J. CLIN.MICROBIOL.

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LETTERS TO THE EDITOR 2381

LITERATURE CITED

1. Brumfitt, W., and J.Hamilton-Miller. 1989.Methicillin resistant Staphylococcus aureus.N.Engl. J. Med.320:1188-1196. 2. Campos, J. M. 1988. Detection ofS. aureus colonization using a

selective medium. Diagn. Test. Alert 4:23.

3. Cookson, B., B. Peters, M. Webster, I. Phillips, M. Rahman, and W. Noble. 1989. Staff carriage of epidemic methicillin-resistant Staphylococcus aureus. J. Clin. Microbiol. 27:1471-1476.

4. Sautter,R.L., W. J. Brown, and L. H. Mattman. 1988. The use ofa selective staphylococcal broth vs. direct plating for the recovery of Staphylococcus aureus. Infect. Control Hosp. Epi-demiol. 9:204-205.

Robert L. Sautter Lester W.Wells

Departmentof Pathology Harrisburg Hospital

Harrisburg,Pennsylvania 17101 Author's Reply

I am glad that Sautter and Wells approve of the use of broth enrichment andagreethat the method hasoften been ignored in studies of methicillin-resistant Staphylococcus aureus (MRSA), although the increased sensitivity ofthe method in thedetection ofS. aureus was noted many years ago. Polakoffet al. (5)detected additional sites ofS. aureus carriage in 361 patients screened with abroth enrichment method: 18(22%)nasal, 22(92%) axillar,74(92%)hand, and 9 (56%) perineal carriers. The method can be made ex-tremelycost-effective ifmultiple swabs areimmersed inthe samebroth,asoneoften needstoknow whether, rather than where, a subjectcarries MRSA(3).

However, there are other issues thatmustbe discussed. Lidwell (4) has suggestedthatthe carriage detectedby broth alone might be light and perhaps temporary, but such detectionmayrevealreservoirsormodes oftransmission of MRSA(2) andpatients otherwise thoughttobe clearduring or following decontamination (3). Moreover, the potential forpatientstobecome infected isnotnecessarily relatedto the amount of S. aureus carriage (8) or whether it is intermittent orpersistent (7).

Brothculture also reducestheincidence of false-negative cultures duetopoorly takenswabs, delayed swabtransport tothelaboratory,unevendistribution of S.aureusorganisms at a site (6), and contamination from an unscreened site. Many of these possibilities were thought tobe relevant to our own

findings

(B. Cookson and I. Phillips, J. Appl. Bacteriol. Symp. Supply, in press), in which broth enrich-mentalone detected MRSA carriage in subjects infected (9 of 26), colonized (17 of 40),oronly transiently carrying(44of 51) MRSA.

Anothercriticism of broth enrichment is thedelay in the issue of the final report vis-à-vis the time required for reporting direct swab culture. However, MRSA detection usually requiresaselective medium, e.g., added methicillin

at5

mg/liter,

anddirect cultureonsuchmedia often requires

48 hofincubation (inup to40%of cases in myexperience). Incubation in abroth increases the inoculum sizesothat a result willusuallybe seen after 24 h of incubation on such a

medium. Thus, there is often no difference between the two methods in the time taken toobtain aresult.

Unfortunately,broth enrichment detects large numbers of staff transiently carrying MRSA (Cookson and Phillips, in press), usually because screening isdoneafteraduty period (2). Time is better spent inspecting staff for lesions (often minor ones can be heavily colonized). Transient MRSA staff carriage is a fact of life often missed in previous studies becauseof thefailuretousebroth enrichmentorthetiming of screening(2). Certainmeasures should be considered to control continuedspread via this route. These might include the wearing of masks for dressing procedures and the cohortingof staff to MRSA patients,dependingon resources and the sort of patients on the involved wards. A more recentapproach, whichIhaveusedsuccessfullyin a number of surgical wards,isselectivecohortingortargettednursing, in which certain high-risk procedures (e.g., wound dress-ings)are performed on MRSApatients only by designated staff, who must not

perform

such procedures on

patients

clearof MRSA. Decontamination of staff after aperiod of nursing MRSA patients also hastobeconsideredif thestaff are toperform close contactproceduresonpatientsclear of MRSA in another wardor

hospital during

thenext24 h. This isofparticularrelevance to agency staff(1).

LITERATURE CITED

1. Cookson, B.D. 1988. Problems of agencystaff incurrent prob-lems withmethicillin-resistantStaphylococcus aureus.J. Hosp. Infect. 4:381-392.

2. Cookson, B.,B.Peters, M. Webster,I. Phillips,M.Rahman,and W.Noble. 1989. Staff carriage of epidemic methicillin-resistant Staphylococcusaureus.J.Clin. Microbiol. 27:1471-1476. 3. Cookson, B. D., M. Webster, and I. Phillips. 1987. Control of

epidemic methicillin-resistant Staphylococcus aureus. Lancet i:696.

4. Lidwell,O.M.1982.Some aspects of the transfer andacquisition ofStaphylococcusaureusin hospitals, p. 175-202. In A. Mac-donald and G.Smith(ed.), Thestaphylococci: proceedingsof the AlexanderOgston CentennialConference. AberdeenUniversity PressLtd., Aberdeen, Scotland.

5. Polakoff, S.,I. D. G.Richards, M. T.Parker, andO. M. Lid-well. 1967. Nasal and skin carriage ofStaphylococcus aureus by patients undergoing surgical operation. J. Hyg. 65:559-566.

6. RidleyM. 1959. Perinealcarriage ofStaph. aureus. Br.Med. J. 1:270-274.

7. Sewell, C. M., J. Clarridge, C. Lackn,E.J. Weinmann,andE.J. Young. 1982. Staphylococcalnasal carriage and subsequent in-fection in peritoneal dialysis patients. J. Am. Med. Assoc. 248:1493-1495.

8. Yu, V. L., A. Goetz, M. Wagener, P. B. Smith, J. D. Rihs, J. Hanchett,andJ. J.Zuravleff. 1986.Staphylococcusaureusnasal carriage and infection in haemodialysis: efficacy of antibiotic prophylaxis. N.Engl. J. Med. 315:91-95.

B. D. Cookson

Divisionof Hospital Infection Central Public HealthLaboratory Public HealthLaboratory Service 60ColindaleAvenue

LondonNW9 5HT England

VOL. 28,1990

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JOURNAL OFCLINICAL MICROBIOLOGY'.July 1989. p. 1471-1476 0095-1137/89/071471-06$02 .00/0

Copyright © 1989. American SocietyforMicrobiology

Staff

Carriage

of

Epidemic Methicillin-Resistant

Staphylococcus

aureus

BARRY COOKSON,1: BARRY PETERS,'- MARGARETWEBSTER,' IAN PHILLIPS,1 MARY RAHMAN.- ANDWILLIAM

NOBLE-Diviision

ofMicrohiologyl

aliidllnstitlte oj Derfil(ZtologV . UMDS,

St.

Thoinas'

Hospitall

LondIon

SEl

7EH,

England

Received2') December1988/Accepted 10March 1989

Twenty-six nurses were repeatedly screened for carriage of epidemic methicillin-resistant Staphylococcus aureus(EMRSA) immediately before and after duty periodsinwhich they solely attended sixpatients widely

colonized withtwo EMRSA strainsdistinguishable by plasmid analysis. EMRSAcarriage wasdetected in 13

nurses. Three EMRSA carriage patterns emerged: transient carriage in 12 nurses, when the EMRSA was

isolated fromnoses orfingers ofnursesafterduty butwasgonebefore theirnextday's duty; short-term nasal carriage, seen on occasion in 4 of these 12 nurses, when EMRSA carriage wasdetected on twoconsecutive

screens; and persistent nasal carriage, seen in 1 nurse only, when the EMRSA was seen on more thantwo

consecutive occasions.Ailbutoneof these incidents ofcarriage couldbeexplained by close patient, ratherthan environmental, exposure and occurred despite an intensive control programme. Transient or short-term

carriage innursesprobably resulted in transfer of the EMRSA between patients. Staff decontamination should

be consideredfollowingaperiod of cohort nursing of EMRSA patients, especially ifstaff membersareshortly

tonurse unaffected patients. Our findings may explainsomeof the difficultiesincontrolling EMRSA.

In recent years nosocomial outbreaks of methicillin- and

multiple-antibiotic-resistant Staphvlococciisaureus (MRSA)

have become a major infection control problem. Although

MRSA strains have notbeen showntobemorevirulent than

otherstrains of S. auraes,(12, 18), very highmortality rates

forpatientswith MRSA infectionshave been reported from severalcenters (2, 16).Our inability to treatthese infections

atanearly stagewithfirst-choice antibiotics and the limited choice anddelayinappropriate systemic chemotherapypose

serious therapeutic problems. Many hospitals in the United Kingdom, includingtwo inour own HealthAuthority, have

experienced a number of outbreaks ofpatient colonization

and infection withepidemic MRSA (EMRSA) which

resem-ble Australian strains (6, 22). EMRSA strains may spread

readily, and some hospitals have found them particularly

difficult to contain (3). Others have commented on the

paucityof information onMRSAcarriageor on the relative

importance of the environment and staff in MRSA spread (4). We reported the phenomenon oftransient MRSA

car-riage (5) during our first EMRSA outbreak. The establish-ment ofan isolation ward forEMRSA patients with cohort nursing provided an opportunity to study the dynamics of the first stages in the spread of EMRSA.

(Part of this work was presented in a poster at the Proceedings of the Third European Congress of Clinical Microbiology, TheHague, TheNetherlands, 1987,abstr.no.

63, p. 34.)

MATERIALS AND METHODS

Study population. Six patients (see Table 1) carrying the

EMRSA were transferred to a ward designated for them at

the South Western Hospital, a hospital with predominately

elderly-care patients situated about 3 mi (ca. 4.8 km) from St. Thomas' Hospital. The ward had acentral corridor with

* Correspondingauthor.

Present address: Department of Immunology. St. Mary's

Hos-pital MedicalSchool. London W2 1PG. England.

eight single-bed rooms, a nurses' office, clean and dirty

utility rooms, and a patients' day room. There was no

controlled ventilation.Althougheachroomhad itsownwash basin, communaltoiletand bathroom facilitieswereused for

ambulant patients and individual commodes were used for those confined totheir rooms (patients D andV).

Twenty-six nurses and two domestic staff members worked solelyon this ward during the 7-week study period.

There werealso twophysiotherapists, who had administra-tive duties butnopatientcontactelsewhere,andtwodoctors allocated, although not solely designated, topatients in the isolation ward.

Three of the patients(D, R, and V)were involved inone

outbreak with a chloramphenicol-susceptible EMRSA, and

three (C, H, and M) were involved in an outbreak with a

chloramphenicol-resistant EMRSA (see Table 1). All were

elderly-care patients, except for patient C. who was

trans-ferred froman acute-care ward.

Decontamination regimen. All patients were

decontami-nated each day with a total-body wash with triclosan

(Aquasept; Hough Hoseason)andtwotriclosanapplications

to the face, nose, axilla, and groin, and chlorhexidine dressings(Bactigras;Smith andNephew)wereappliedtoall infected lesions. Staff members were decontaminated with

four nasal applications of neomycin and chlorhexidine (Naseptin; ICI) and a total-body wash with chlorhexidine

gluconate (Hibiscrub; ICI) only when they left thewardfor the final time.

Screening. Patients were screened for MRSA at least weekly with peptone water-moistened swabs from nose,

throat, perineum, catheter sites, and any abnormal skin or

wounds. Nurses took their own peptone water-moistened nasalswabs before andaftereach8-to 10-hduty period for the 7 weeks, and 240 finger swabs were taken in the last 3

weeks of the study. The physiotherapists were screened

immediately before and after each of 12 physiotherapy sessions involving all patients. The domestic and medical staff memberswerescreenedatthebeginningand endofthe

1471

(4)

1472 COOKSON ET AL.

study, and the latter were also screened after examining patients on two occasions. At least once weekly, nose, throat, and perineal swabs were taken from each nurse and examined for methicillin-susceptible S. auireus (MSSA).

Swabs were usually transported and processed on the same day. All media were made with Columbia agar base (CM331;OxoidLtd.). Swabs for MRSAscreeningwerefirst inoculated directly on mannitol salt agar (CM85; Oxoid) containing 5 mg of methicillin per liter (MSM) and then placed in salt broth (no. 2 CM67, with 7.5% added sodium chloride;Oxoid), which was subculturedon MSM after24h. These subcultures were incubated at 37°C, the plates were examined after 24 and 48 h, and mannitol-fermenting colo-nies were tested for coagulase. Swabs for the screening of MSSA were inoculated directly on blood agar with a 10-pg methicillin disk (BAM) and then placed in salt broth, which was subcultured after 24 h on BAM; all BAM plates were incubated for 48 h at 30°C, and any staphylococcal colonies were tested for coagulase.

Antibiotic susceptibilities of all S. aureus isolates were determined on lysed blood agar by the

comparative

disk diffusion method.

Each nurse recorded the procedures she

performed

each dayonpredesigned forms,sothat acquisitionof the EMRSA could be correlated with activity. The degree of staff EMRSA exposure was divided into three grades, and the overallgrade for each day was defined by the

highest

grade ofprocedure performed on thatday.

(i) Grade 1 was superficial contact-brief exposure to a contaminated environment but no direct contact with a

colonized or infected patient, e.g.,

delivering

meals or

speakingto a patient.

(ii) Grade 2 was casual contact-patient contact but no manipulation of colonized or infected sites, e.g., helping patients to wash and dress themselves.

(iii) Grade 3 was close contact--physical contact with infected orcolonized sites, e.g., changing wound

dressings,

bathing widely colonized patients, or urethral catheteriza-tion. Our infection control policy included theuse of aprons and gloves for all contact

procedures,

but apart from chest physiotherapy, masks were not used by stafffor any close-contactprocedureswith these

patients.

Theinfection control team repeatedly emphasized the

importance

of

appropriate

hand decontamination with chlorhexidine

preparations

(Hi-biscrub and Hibisol; ICI) after

patient

contact but did not

inform staff members of their carriage unless it was

persis-tent (see Results).

Environmental screening. The environment was screened onceeach weekbefore ward

cleaning,

whichwas

performed

oncedaily duringthe first 2weeks and twice

daily

thereafter. Airfrom eachpatient's room, the nurses'

station,

corridors. and the day room was sampled with a

portable

air

sampler

(Surface Air System; Cherwell

Laboratories);

180 liters of air was sampled in 1 min on MSM and BAM

plates.

In the last 3 weeks of the study 900 liters of air was

sampled

in 5 min; phenolphthalein phosphate (SR31;

Oxoid)

agar

plates

were substituted for BAM plates. Peptone water-moistened swabs were used to sample floor dust,

windowsills,

bed-steads, andpointsoffrequenthandcontact,suchasthe

drug

trolley, nurses' patient card index system,

telephone,

taps, doorhandles andlightswitches.These swabswere

plated

on MSM and then placed in salt broth. BA and MSM settle plates(4.5-in. [ca. 11.4-cm]diameter) wereleftatfloor level

for2h, 2and8ft(ca.61and244cm,

respectively)

from each

patient's bed, and others were left in the

corridor,

nurses' office, utilityrooms, andday room.

Weekly

MSMsweepor

impression plates

weretakenat

patients'

bedclothes and on

30 occasions in the last 3 weeks from nurses'

disposable

aprons andclothes.

Strain identification. The

identity

ofEMRSA isolates was

confirmed

by

a characteristic antibiotic

susceptibility

and

phage

typing

pattern

(6).

Plasmid

analysis

was

performed

as

previously

described

(7)

on all EMRSA isolates from staff

membersonEMRSAisolatesfrom

patients

atthestartofthe

study

and whenever the

chloramphenicol

susceptibility

pat-tern

changed. Phage

typing

was also

performed

on MSSA

isolates

by

the

Staphylococcus

Reference

Laboratory

of the Central Public Health

Laboratory,

Colindale,

London,

En-gland.

Statistical

analysis.

An

unpaired

t testwasusedtocompare the mean of the number of

days

of each

activity grade

and the mean of the number of each

grade

of

procedure

per-formedoneach

day

fornurseswhocarriedtheEMRSA with the

corresponding

means for nurses who never carried it.

Days

ofcarriage wereassumedtofollowaPoisson

distribu-tion,

with the mean

being dependent

on the numberofeach

grade

of

procedure

performed.

The interaction ofthe

num-berof

procedures

(grade

2or

3)

performed by

each nurse on

each

patient

was then

investigated

with the computer pro-gram GLIM3.77

(GLIM

system release

3.77, 1985,

C. D.

Payne, ed.,

Numerical

Algorithms Group,

Oxford).

RESULTS

Strain identification.

All

MRSA

phage typed

weakly

with

phage

85atRTD100

(routine

testdilution x

100)

and with the

experimental phages

88A and 932.

Plasmid

analysis,

unlike

chloramphenicol

susceptibility testing, reliably

distinguished

between thetwooutbreak strains

(Fig.

1).

Chloramphenicol-susceptible

isolates from

patients

D,

V,

and R

always

contained a ca.

1-megadalton

(MDa)

cryptic

plasmid

and

were

designated

CY. Plasmid

analysis

of isolates from

patients

C,

M, and H, with the

chloramphenicol-resistant

EMRSA,

always

revealed a ca. 3-MDa

plasmid,

and these

isolates were

designated

CR.

However,

a

minority

popula-tion of

chloramphenicol-susceptible

isolates was

occasion-ally

detected fromsomesiteson

patients

C and

M,

and these

had

merely

lost the 3-MDa

chloramphenicol

resistance

plas-mid

(designated

CR-).

Patient EMRSA carriage. Table 1

gives

details of

patient

colonizationand infectionwith the EMRSA and the approx-imate time taken to

perform

wound

dressings.

The most

heavily

colonized

patient,

D, died on

day

23 of the

study.

Table 1 alsolists the residual sites colonized after the first2 weeks of decontamination. The decontamination

regimen

produced

adiminution in theextentof EMRSAcolonization

by

week 3 in all

patients

except V, in whom the

triclosan

caused folliculitis and had to bediscontinued.

Environmental

screening.

Environmental EMRSA isolates were obtained

only

in thefirst four

weekly

screensandwere

neverisolatedfrom theroomof

patient

Morinanyof the slit

samples

of ward air.

Settle

plates

in the first 3 weeks indicated alow contamination rate of between1and 2 CFU of EMRSA per h in the roomsof

patients

D and R, inone

instance

immediately

aftera

change

of

patient

D's

dressings.

Only

onesurface swab was

positive

on adirect

culture;

two

colonies of EMRSA were isolated from the taps and door

handle ofthe room of

patient

C, the most mobile of

all

the

patients.

All other

positive

results were from broth enrich-ment cultures of swabs. These indicated

widespread

but low-level EMRSAcontamination inthedust in the roomsof

(5)

STAFF CARRIAGE OF EMRSA 1473

FIG. 1. Ethidium bromide-stained plasmid agarose gel. Lane 1

contains themolecular size standards;al plasmidswereof thesizes

previously reported (7). Theca. 20-MDa plasmid carriesgenes for

resistance to ethidium bromide. propamidine isethionate. several aminoglycoside antibiotics, and often trimethoprim and penicillin (6). CY isolates have ca. 20- and 1-MDa cryptic plasmids. CR isolates have ca. 20- and 3-MDa chloramphenicol resistance plas-mids;anopencircularform of suchaplasmid isalsopresent. CR-isolateshave only theca.20-MDaplasmid. CRCY isolates have the ca. 20-, 3-, and 1-MDaplasmids.

cm) from the bed of patient D. Less contamination was

found in the rooms of patients V and H. where only horizontal surfaces less than 2 ft (ca. 61 cm) from the bed

were positive, and that of patient C where, in addition, a

windowsill 8 ftaway waspositive. EMRSAwasnotdetected

on the nurses' clothes or aprons. The environmental EMRSAisolateswereofaplasmidtypeconsistent withthat found forthe patientin that room.

Staff carnage. Neither physiotherapist acquired the

EMRSAdespite close patientcontact. However, the

proce-duresthey performed, suchasmobilizationorchest

physio-therapy,wererarely classifiableasgrade 3.Themedicalstaff

memberswerealsoclear of carriage,buttheirenvironmental

and patient contact was minimal. The domestic staff

mem-TABLE 2. EMRSAcarrigeand dutydaysof nurses 1 to 13 No.ofacquired No.of dutv No.of clear screens: EMRSA of activitydayswith

of

plasmid

type: grade:

Nursegre

Before After the

carriage lastcarnage CR CY CR CY 1 2 3

episode` episode

1" 17. 33NF 8 1 2 O 6 12 10

2'> 10 34 1 0 0 1 8 il

3 39,.1.33, 8 2 4 0 0 7 14

il

41" 1.27 5 1 1 0 0 8 9

5'" 2+.6. 3. 6 0 8 O O 8 10

11F, 3F. 1F.IF

6 1+.42 4 1 2 0 0 10 12

7 4+.5, 5.31 4 3 2 O O 12 9

8h 0+, 1,3.1. 4 1 4 1 0 2 7

9 11.7 36 0 2 0 7 15 6

10"' 19 S 1 0 0 0 6 5

il 1.13 26 1 1 0 0 10 12

12 13 8 1 0 0 0 6 6

13' ' 0 0 8

`All nasal and transient carrigeexceptas follows:NF. nasal andfinger

carriage; F.fingercarriage alone: +. short-termEMRSA carriage. ' Also carriedanS. aureusisolate resistantonlytopenicillin.

Persistentcarrier.

bers werealso clear of carriage despitetheirenvironmental contact.

A total of 870 screens were performed on the 26 nurses, and EMRSA carriagewas detected on 50occasions in 13of them. Threecarriage patternswereobserved in the 13nurses (Table 2).

(i) Transient carnage. Nasal or finger EMRSA carriage wasdetectedimmediately after a duty period butwaslostby thenextday. Thistypeofcarriagewas seenon32occasions innurses1 to 12andwasmostlynasal;EMRSAwascultured ononly 5 occasions from two nurses' fingers.

(ài) Short-term nasal carnage. EMRSA was detected on two consecutive occasions. In three of the four nurses in whom this type of carriage was observed, the EMRSA was detected before and after the same duty period.

Only 4 of the 40 instances of transient or short-term carriage were detected by direct culturing, andin each less than 17 colonies of EMRSA were grown. Table 2 includes details of the number of clear screens before each culture and after the last culture of EMRSA.

TABLE 1. Patient sitescolonized or infected with the EMRSA and EMRSA transmission to staff performing grade 3 procedures

No.ofgrade3 7c ofgrade3

Site(s) colonizedorinfected by EMRSA" procedures performed proceduresperformed Approxtime (h)

Patient (no. of dressingschanged) %(- of dressings taken to change

bynurses: changed)bynurses1 dressings to12 resulting in

Initially After wk 2 14to26 1to12 EMRSAacquisition

V N,ThP.U,R,H+.S+ Ail 17(4) 71(48) 6(4) 1

D N,Th, P.S+, H+, H+ 37 (12) 103(72) 13 (13) 3.5

R N.Th, P, U, R,S+.H+, H+ H+, H+ 28 (10) 73 (41) 7 (12) 1.5

C N. Th, PU.S. A+ A+ 13 (8) 47 (26) 11(12) 1

H N. S, U+ T+ 24 (7) 59 (14) 10 (29) 0.5

M N,P,Th,R. U+ P.R. U+ 31 (5) 33 (7) 0 (0) 0.5

'A,Abdominal wound; H. heel sore;N.nose;P.perineum;R.rectum;S. sacrailsore:T.toesores; Th. throat; U.urethra. +.Infected site.-. The patient died.

(6)

1474 COOKSON ET AL.

(iii) Persistent nasal carriage. EMRSA was isolated on three or more consecutive occasions. This typeofcarriage was seen in only one nurse (nurse 13);EMRSA wasisolated onfour and then sixconsecutiveoccasions, although in only two of these occasions was EMRSA detected by direct culturing. This nurse wassubsequently foundtobecarrying the chloramphenicol-resistant EMRSA in her throat and perineum and to be taking a course of trimethoprim and sulfamethoxazole for a urinary tract infection. Hercarriage was subsequently cleared with mupirocin (Bactroban; Beecham Pharmaceuticals). One chloramphenciol-suscep-tiblestrain was isolated from thisnurse(Fig. 1,CR-)but,as with the isolates from patients C and M, this was a CR isolate which had lost the chloramphenicol resistance plas-mid. No other nurses carried the EMRSA at other sites in their weekly screens. We were unable to determine when nurse 13 became a persistent carrier, so she was excluded from the data on EMRSA acquisition. EMRSA carriagewas detected in6% of the screens of the 25 nursesthusanalyzed and 11% of the screens ofnurses 1 to 12.

NoEMRSAacquisition was detectedafter any of14grade 1activity days and after only 1 of 196 grade2 activity days. In marked contrast, grade 3 activity days were associated with all other incidents of transient or short-term EMRSA carriage. There was no significantdifference in the number ofgrade2 (P = >0.2) or three (P = >0.2) activity days for nurses 1 to12, whocarried the EMRSA, and nurses14to26, who did not. However, nurses1 to 12did perform far more wounddressings (P<0.02)andgrade 3activities (P<0.001) on grade 3 days than did nurses 14 to 26 (Table 1). The number of grade 3 procedures performed significantly (P <0.001) increased the mean number of days of EMRSA carriage by nurses, but the differences between patients were notsignificant (P > 0.05).

Table 2 shows the plasmid patterns of the EMRSA ac-quired by nurses 1to 12. Plasmidanalysis confirmed that all thechloramphenicol-susceptible strains had the CY pattern. Thus, we wereable to show that thetwo EMRSA outbreak strains had been acquired at different times in seven of the nurses rather than that there was continued carriage of the CR strain with plasmid loss. Nurse 5 is

particularly

worthy ofcommentin thatsix of hereightCY strainsweredetected solely at the end of duty periods in which she treated only patientswith the CY EMRSA plasmid profile. It was impos-sible to ascertain in two of the four incidents of short-term carriage whether the EMRSA strains had been

reacquired

or

persisted during the duty period, as they had the same plasmid pattern (CR).In athird incident (nurse8)the strains differed in plasmid patternin thatone wasCR and theother was CRCY (containing both cryptic and chloramphenicol resistanceplasmidsandacquiredfrompatient V;seebelow). It appearsthatthis patternwasderivedfrom in vivo

plasmid

transfer between the strains with patterns CR and CY rather than that the two strains were detected at the same site, althoughthesestrains havenotappearedtobe very stableon serial subcultures, even on media containing 50 mg of chloramphenicol per liter.

In 33of the instancesof staff EMRSAacquisition,plasmid analysis enabled us to implicate procedures on

specific

patients. EverypatientexceptMwasinvolved

(Table

1).

and patientD was responsibleformost ofthetransmission

(Fig.

2), but moregrade3 procedureswere

performed

onher. No obvious relationship could be observed between EMRSA transmission to staff and the length ofthe wound

dressing

procedureortheextent of EMRSAcolonization ofpatients. Forinstance,thegreatest percentageofdressingprocedures

No. of EMRSA transmissions

12

-10

-

8-6

-PattentDdled

1 2 3 4 5 6 7

Week of Study

Key _D

eylC MR MV EMH Total

Patient codes

FIG. 2. Patients implicatedeach week in EMRSA transmission

tonursingstaff. The histogramcodes represent eachpatient (Table 1) that could be implicated in that study week for an EMRSA transmissionto a nurse.The dotted line represents the totalofsuch

transmissions.

followed

by

EMRSA transmission to staff occurred with

patient

H, a

minimally

colonized

patient,

who

required only

brief wound

dressing

of infected toe sores. MSSA was

detected in nurse 13 and six other nurses in whom the EMRSA was also detected

(Table 2).

Phage

typing

distin-guished

amongallthe

isolates,

except thoseofnurses 5and

8.

EMRSA transmission betweenpatients.

Acquisition

of the CR EMRSA in

patient

R's sacral sore and

perineum

and

patient

V'ssacralsore

(both

patients

werecarriersoftheCY

strain)

occurred in week 1of the

study.

A

chloramphenciol-resistant strain with the CRCY pattern wasalso isolated at this time from

patient

V's

perineum.

The

acquired

strains did notestablish themselveson these

patients

in that

they

were

not isolated from screens

repeated

48 h later or from

subsequent

screensin thenext6weeks. Nurse

13,

colonized

with the EMRSA with the CR

plasmid profile,

did not

perform

any

procedures

on either of these

patients,

and the

EMRSA was

thought

to have been transmitted to these

patients by

nurses with transientor short-term

carriage.

DISCUSSION

Ithasoften been

suggested

thatcertain

epidemic

strains of S.aiireushavea

special

ability

tocolonize

patients

and staff

(20)

and that certain MRSA strains

(EMRSA)

are among these

(6).

There is little information on the

carriage

and transmissionofMRSA,and inarecentreviewofthe

subject

CasewellandHill

(4)

hadto

extrapolate

from theconclusions of studies ofthe carriage of

MSSA,

but even in these there

has been no

comparable

attempt to correlate staffcarriage

withduties

performed.

Inthis

study

we were

presented

with

an

opportunity

to examinestaff EMRSA

acquisition

andthus

the

early

stages of its

spread.

A number of factors contributed towards the success of

this

study.

Firstly,

nurse

cooperation

was achieved

by

intensive education and the useof

personal

activity

sheets.

Secondly,

many wound

dressing procedures

were of such a

long

duration that thenurses involved would often

perform

grade

3

procedures

on

only

one

patient

on any

given day.

Thirdly,

the

twice-daily

screening of each nurse

yielded

(7)

STAFF CARRIAGE OF EMRSA 1475

much more detailed information than that obtained in most

other studies, in which intermittent

screening

has been the

norm.

Fourthly,

we used broth enrichment

culturing

to

increasethe

sensitivity

ofdetection of EMRSA carriage; in

fact,

without it carriagewould have been

entirely

missed in

eight

ofour nurses.

Finally, plasmid

analysis

enabled us to

distinguish

amongtheoutbreak strains and

clarify

thesource

of

carriage.

We were fortunate that the strains did not

extensively

cross-colonize the

patients

and that the cryptic

plasmid

wassuch astable marker. Theemergenceofathird EMRSA

plasmid

type

(CRCY)

during

the

study

is

interest-ing, especially

as it is very rare in the United

Kingdom

(J.

Naidoo,

personal

communication).

However, this pattern

predominated

in MRSAfromoneof the Australian

hospitals.

where similar ifnotidentical strains have been described(6,

23).

Our

study, although

detailed, was not

designed

to avoid the

possibility

of it

causing

an alteration in the nurses' behavior

(the

Hawthorne

effect)

in that weeducated

highly

motivated nurses in the

importance

ofcorrect

procedures

and hand

hygiene

and

they

screened themselves.

Despite

this,

the incidence of transient and short-term carriage was

unexpectedly high.

EMRSA

acquisition

was almost

totally

related to close

patient

contact,

especially

wound

dressing.

rather than

walking

into a contaminated environment or

having

minorcontactwitha

patient

(grade

1or2

activities).

Seven of twelve nurses carried each

epidemic

strain at

different

times,

supporting the

hypothesis

of continued

ac-quisition

rather than intermittent detection of EMRSA

car-riage.

This

hypothesis

was also

supported by

the

large

number of clear screens between each EMRSA carriage

episode

in many of our nurses and

by

the fact that the EMRSA was

predominantly

detected

after,

rather than

before,

a

duty period.

We did not

perform

regular

finger

sampling

or screening

immediately

beforeandafter

procedures

in this

study

andso

cannot comment on the exact method of EMRSA

acquisi-tion. The observation that EMRSA transmission was not

simply

relatedtotheextentof

patient

colonization butcould follow

simple dressing

procedures

on

minimally

colonized

patients

made itdifficult to

predict

which

patient

was

likely

to transmit the

organism.

S. aureus carriage on

fingers

has been correlated with

perineal

carriage

(11),

which was not evident in either ofourtwo nurseswith

finger

carriage,and with nasal carriage

(17),

as was observed in one nurse. Nor did

they

have any colonization of minor lesions or overt

infectionwith the EMRSA. The

persistence

of MRSAonthe hands of

nursing

staff and its

subsequent

clearance

by

simple

handwashing

ordisinfection have been demonstrated

previ-ously

(21).

The EMRSA mayhave been

acquired

fromdirect contact with contaminated wounds or

dressings

and

bed-clothes,

as Hare

(10)

hypothesized.

We feel that this is

unlikely

in that

gloves

were

usually

worn for contact with

patients, judging by

the

large

numbers thatwereusedduring the

study.

We could not demonstrate contamination of nurses' clothes. It is more

likely

that the EMRSA was

acquired

frominhaledairborne EMRSA

particles

suchaswe have observed

during physiotherapy

on apatient with exfo-liative dermatosis

(5)

and after wound

dressing

and bedmak-ing

(B.

D. Cookson,

unpublished

observations). EMRSA transmission would then

presumably

follow transfer from the nose tothe hands.

The definitions used in other studies have differed from

ours because of the lower

frequency

of

subject

sampling used. The first allusion that we found to brief S. (lure(s

carriage

was in a

weekly

study

of nasal carriage in 500

medical studentsover a3-to12-monthperiod(9); 42%c of the students were 'occasional' carriers in that the organism wasdetectedinless than 10% of theirscreens.Theseisolates were ofa phage type different from that previously found, and these workers postulated that these students' noses

were not trueS. auraeshosts but acted rather like filters of the inspired air.

The further elucidation by this study of the phenomenon oftransientorshort-term EMRSAcarriage hasanumber of implications. These forms of carriage probably caused the two instances of EMRSA transfer from one patient to anotherinthat the patients had no contact with each other, the persistent carrier (nurse 13) had no contact with these patients. the environmental contamination did not extend outsidetheroomsof thesepatients, and nofomites could be implicated. We are also convinced that they have contrib-uted tothe failureof standard isolationtechniquestocontrol EMRSA spread. These observationsjustify the use of des-ignated staffwhen the consequences of EMRSA transmis-sion may be especially serious, such as in an intensive-therapy unit(5) or aburn unit (16).

Transient MRSAcarriage in agency staff members might also result in interhospital spread, as these staff members often work in more than one hospital in a 24-h period. A central agency coordinatesthe employment ofallouragency nurses and ensures that we do not employ staff members who haveworked on EMRSA patients elsewhere unlessthey havebeen screenedand decontaminated. A similarapproach is adopted with our own staff nurses who have had close contactwith EMRSA patients.

AIl threetypes ofcarriage shouldbe consideredin MRSA clearance studies with antibiotics or disinfectants. Such studiesrarelystate whether screens were performedonstaff members immediately afterthey had performed procedures on patients. Thus. transient carriers may have been misla-beled aspersistent carriers, leadingto erroneousconclusions as tothe efficacy ofspecific decontamination regimens. We have not previously found chlorhexidine, povidone iodine, orhexachloropheneused alone to be effective ineradicating the EMRSA from wounds. The relationship between staff EMRSA acquisition and wound dressings emphasizes the importance of rapid elimination from wounds. We agree with others (24) that thrice-daily triclosan total-body washes or baths are poorly accepted by patients. Furthermore, tri-closan did not eradicate the EMRSA from our patients' wounds,although only minimal wound exposure would have occurred duringa bath, since dressings were not removed.

Although it was clear that the performance of close-contact (grade 3) procedureswas the mostimportant differ-ence betweennurses1 to 12andthose who did not carry the EMRSA, we could not be certain that other additional factors did not exist. Others have pointed out the possible roles of human leukocyte antigen type (13) and bacterial interference (19) in the carriage ofS. aureus. Only weekly screenswereperformedforcarriage ofMSSA, sowecannot be certain of the dynamics ofbacterial interaction, but it is interestingthat ailthecarriersof MSSA were also carriers of the EMRSA. Bacterial interference might have discouraged the establishment ofprolonged EMRSA colonization, but is unlikely tobe the soleexplanation in that half of nurses 1 to 12 did not carry such S. aureus strains. The association between antibiotic administrationand MRSA acquisition in patientshas beenalludedtopreviously (8); it might alsohave been a factor in staffacquisition, as in nurse 13.

(8)

1476 COOKSON ET AL.

azjreus (1, 14, 15). Areas immediately around the beds of our EMRSA patients usuallyharbored the organism. In contrast, the more outlying areas were clear, despite the use of these areas formobilization and rehabilitation. People commonly blame the environment as the source of EMRSA spread, but we demonstrated that walking into a contaminated environ-ment alone didnot lead to EMRSA acquisition. In situations similarto ours, we are confidently able to predict that staff members are unlikely to acquire EMRSA unless a close-contact (grade 3)procedure is performed. We have therefore concentrated our efforts on those procedures most likely to cause EMRSA transmission by the designation of nursing staffand have minimized the control measures imposed on the other staff.

It seems probable that many of our observations are common toall outbreaks of staphylococcal infection. How-ever, one must take care when extrapolating the results of this study to different circumstances. Other hospitals may have a more heavily contaminated environment. Con-versely, in an open ward, even with minimal environmental contamination, staff members may be at risk via the airborne route when passing close to an area where a close-contact (grade 3) procedure is being performed. Further studies of similar detail and intensity of screening, but with different environmental and staffing conditions, are required. Un-doubtedly, the use of plasmid analysis and an activity grading system wouldfacilitate such studies.

ACKNOWLEDGMENTS

Wethank theStaphylococcus Reference Laboratoryforthe phage typing, S. Chinn for the statistical analysis, and al the staffwho participated in this study.

LITERATURE CITED

1. Ayliffe, G. A. J., V. G. Aider, and W. A. Gillespie. 1959. The disinfection of bath water with hexachlorophene. Lancet ii: 456-458.

2. Boyce, J. M., M. Landrey, T. R. Deetz, and H. L. Dupont. 1981. Epidemiologicstudies ofanoutbreak of nosocomial methicillin-resistant Staphylococcus aureus infections. Infect. Control 2: 110-116.

3. Bradley, J. M., P. Noone, D. E. Townsend, and W. B. Grubb. 1985. Methicillin-resistant Staphylococcus aureus ina London hospital. Lanceti:1493-1495.

4. Casewell, M. W., and R. L. R. Hill. 1986. The carrier state:

methicillin-resistant Staphylococcius aureus. J. Antimicrob. Chemother. 18(Suppl. A):1-12.

5. Cookson,B.D.,M.Farrington,M.W.Webster,andI.Phillips. 1985. Methicillin-resistant

Staphylococcuis

aureus. Lancet ii: 218-219.

6. Cookson, B. D., and I. Phillips. 1988. Epidemic methicillin-resistant Staphylococcus aureus. J. Antimicrob. Chemother. 24(Suppl.C):57-65.

7. Cookson, B. D., H. Talsania,J. Naidoo, andI. Phillips. 1986. Strategies for typing and properties of epidemic methicillin-resistant Staphylococcus aureus. Eur. J. Clin. Microbiol. 5:

702-709.

8. Crossley, K., D. Loesch, B. Landesman, K. Mead, M. Chern, and R. Strate. 1979. An outbreak of infections caused by strains ofStaphlvlococcusaureusresistantto methicillin and aminogly-osides. 1. Clinical studies.J. Infect. Dis. 139:273-279. 9. Gould, J. C., and E. J. McKillop. 1954. The carriage of

Siaph-vlococcics pyogenes var aureus in the human nose. J. Hyg. 52:304-310.

10. Hare, R. 1960. The transmission of Staphylococcics aureus. Med. Press 6320:544-549.

11. Hare, R., and M. Ridley. 1958. Further studies in the transmis-sion ofStaphylococcusaureus. Br. Med. J. 1:69-73.

12. Keane, C. T., and M. T. Cafferkey. 1984. Re-emergence of methicillin-resistant Staphylococcuis aureus causing severe in-fection. J. Infect. 9:6-16.

13. Kinsman,O. S., R. Mackenna, and W. C. Noble. 1983. Associ-ation between histocompatibility antigens (HLA) and nasal carriage of Staphylococcus aureus. J. Med. Microbiol. 16: 215-220.

14. Lidwell,O. M. 1981. Some aspectsofthetransferand acquisi-tion ofStaphylococcus aureus in hospitals, p. 175-202. In A. Macdonaldand G. Smith(ed.). Thestaphylococci: proceedings of the Alexander Ogston Centennial Conference. Aberdeen University Press, Aberdeen, Scotland.

15. Lidwell, O.M., J. Davies, R. W. Paine, P. Newman, and R. E. O. Williams. 1971. Nasalacquisition ofStaphylococcusaureus in partlydividedwards. J. Hyg. 69:113-123.

16. Locksley, R. M., M. L. Cohen, T. C. Quinn, L. S. Tompkins, M. B.Coyle,J. M. Karihara, and G. W. Counts. 1982.Multiply antibiotic-resistant Staphylococciusaureuis: introduction,

trans-mission, and evolution ofnosocomial infection. Ann. Intern. Med. 97:317-324.

17. Noble, W. C.,H. A. Valkenburg, and C. H. L. Wolters. 1967. Carriage of Staphylococcus aureus in random samples of a

normal population.J. Hyg. 65:567-573.

18. Peacock, J. E.,Jr., D. R. Moorman, R. P. Wenzel, and G. L.

Mandall. 1981.Methicillin-resistantStiaphylococcus aureus: mi-crobiologic characteristics, antimicrobial susceptibilities and assessment ofvirulence ofanepidemic strain. J. Infect. Dis. 144:575-582.

19. Ribble, J. C. 1967. A mechanism ofbacterial interference in vitro. J. Immunol.98:716-723.

20. Shooter, R. A. 1981.Evolution of the hospital staphylococcus, p. 149-155. In A. MacdonaldandG. Smith(ed.),The staphylo-cocci:proceedingsof the AlexanderOgston Centennial Confer-ence.Aberdeen University Press, Aberdeen, Scotland. 21. Thompson,R. L., I.Cabezudo, and R. Wenzel. 1982.

Epidemi-ology of nosocomial infections caused by methicillin-resistant Staphlococcusaureus. Ann. intern. Med. 97:309-317. 22. Townsend,D.E., N. Ashdown, J.Bolton,andJ.M.Bradleyetai.

1987. Theinternationalspreadofmethicillin-resistant Staphylo-cOCCuSaureus. J. Hosp. Infect. 9:60-71.

23. Townsend,D.E.,W. B.Grubb,and N.Ashdown.1983.Genetics of drug resistance in methicillin-resistant Sulphylococcus au-reusfrom Australian hospitals.J. Hosp. Infect.4:331-337. 24. Tuffnell,D.J.,R.S. Croton,D. M.Hemingway,P. N.Hartley,

P. N. Wake, and R. J. P. Garvey. 1987. Methicillin-resistant

Stuphylococcus

aureus;the role ofantisepsis in thecontrolof

anoutbreak. J.Hosp. Infect. 10:255-259.

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