0095-1137/90/010076-07$02.00/0
Copyright ©1990, American Society for Microbiology
Three-Year
Experience with
Sonicated
Vascular Catheter Cultures
in a
Clinical Microbiology
Laboratory
ROBERT J. SHERERTZ,lt* ISSAM I.
RAAD,l
ANUSHABELANI,l
LILIA C.KOO,l
KENNETH H.RAND,'
DEANA L.PICKETT,2 SARA A. STRAUB,2 AND LORETTA L. FAUERBACH2DivisionofInfectiousDiseases, DepartmentofMedicine, University of Florida School of
Medicine,'
andDepartment of Infection
Control,
ShandsHospital,2
Gainesville,
Florida32610Received12July 1989/Accepted18September 1989
Using a quantitative sonication method, we cultured 1,681 consecutive vascular catheters submitted toa clinical microbiology laboratory in a 36-month period. A total of 46% of the cultures werepositive; the most commonorganismsisolated werecoagulase-negative staphylococci (36.4%), Pseudomonas aeruginosa (13.9%), enterococci (10.0%), yeasts (9.2%), Staphylococcus aureus (5.8%), and Enterobacter species (4.4%). The frequencies of positive blood cultures within 48 h prior to a positive catheter culture result were as follows: Candida albicans(68.4%),S. aureus(60%),Enterobactercloacae(42.9%), Staphylococcusepidermidis (32.1%), P.aeruginosa(27.7%), and enterococci (23.3%). The sonication method allowed quantification of the number of CFUremoved froma catheter for between 102 and 107 CFU. For catheter cultures in which :102 CFUgrew, alinearregressionequation could be calculated: (risk of positive blood culture for the same organism) = 14
[loglo(number
oforganisms removedfrom the catheter)] - 21 (r = 0.93). For catheter cultures in which <102 CFUgrew, positive blood cultures for the same organism were strongly associated with a proven infection at asitedistant from the catheter (P =0.001) or probablecontamination (S. epidermidis). Our findings indicate that thistechnique hasconsiderable potentialfor use in clinical microbiology laboratories to aid in thediagnosisofvascular catheter infections and for clinicalinvestigations into thepathogenesisof these infections.
The quantitative relationship between catheter-related
vascular infections and the number of organisms on the
catheter was first demonstrated by the roll-plate culture technique developed by Maki et al. (11). They found that greaterthan 14colonies growingon aplate correlated with insertion siteinfections andthat greater than 1,000 colonies
correlated with catheter-related bacteremias caused by the same organism. These results have been verified by other
investigators(1, 4, 5, 8, 13, 15, 18). Asusefulas theroll-plate
technique has been in obtaining a betterunderstanding of catheter-related vascularinfections, a possible limitation is its inabilitytoquantifymore than 1,000coloniespercatheter segment.
Culturetechniquesthatremoveorganisms from catheters into broth followed by serial dilutions have allowed the recovery andquantification ofa greater number oforganisms than theroll-platetechniquehas (2, 3). Earlier methodsused
in clinical studies involved flushing the catheter with broth
(3) and centrifugingthecatheterinbroth (2). Large numbers
oforganisms removed by either technique are statistically associated with catheter-related vascular infections (P <
0.05).
In this study we used a water bath sonication technique thatwasfirstdescribed and used in vitro by Constantinou et al. (D. Constantinou, G. G. Geesey, and M. Wardle, Abstr. Annu. Meet. Am. Soc. Microbiol. 1981, L13, p. 80). Using
thismethod, we have shown that a wide range of
organisms
canbereproduciblyremovedfromdifferenttypes of vascu-lar catheters in vitro (D. M. Forman, R. J. Sherertz, R.
Johnson,L. C. Koo, and S. O. Heard,Program Abstr. 24th Intersci. Conf. Antimicrob. Agents Chemother., abstr. no.
* Correspondingauthor.
tPresentaddress: Division of InfectiousDiseases,Department of Medicine,BowmanGray School of Medicine,Wake Forest Univer-sity,Winston-Salem, NC 27103.
369, 1984). Subsequently, we used this technique in a
prospective study of Swan-Ganz catheters and found that
removal ofgreaterthan103organisms from the catheterwas
associated with
positive
blood cultures for the same organ-ism(P< 0.025) (7).Encouraged by these results, webegan culturing all vascular catheters submitted to the clinicalmicrobiology laboratory by using sonication in broth fol-lowed by serial dilutions and report here our 36-month experience with this method.
(This investigationwaspresentedin partpreviously [A.K.
Belani,R.J.Sherertz,L. C.Koo, J. M.Getchius, andK. H.
Rand,Abstr. Annu. Meet. Am. Soc.Microbiol. 1985, L2, p.
379; R. J. Sherertz, A. Belani, and K. H. Rand, 26th ICAAC, abstr. no. 1132,1986].)
MATERIALS ANDMETHODS
Catheter culture technique. The study was
performed
in theShandsHospital,a476-beduniversity referral hospitalat theUniversity ofFlorida, Gainesville.Allvascular catheters submitted to the clinical laboratory for culture during a3-year
period
werestudied. No attempt was made tostan-dardizethe methodof catheterinsertion, catheterremoval,
orcathetertransport to thelaboratory,as wewereinterested
in whether the sonication culture method was valid under
realistichospital conditions.
Each catheter was placed in 10 ml oftryptic soy broth (Difco Laboratories, Detroit, Mich.), sonicated for 1 min
(55,000 Hz, 125 W; Ultrasonic Industries, Inc., Plainview,
N.Y.), and then vortexed for 15 s. A0.1-ml sample ofthe broth was added to either 0.9 ml (1:10 dilution, first 12
months)or 9.9 ml (1:100dilution, last 24months) ofsaline and vortexed. Then,0.1 mlof these dilutions and 0.1 ml of thesonicated broth were surfaceplated byusing a wireloop
onTrypticase soy agar with5% sheep blood (BBL Microbi-ologySystems, Baltimore,Md. [Div. BectonDickinson and Co.]) and MacConkey agar (BBL Microbiology Systems).
76
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The
plates
and theoriginal
broth containing the catheter were incubated aerobically in 5%C02
for48 h at37°C,
and then the number oforganisms
was quantitated. Accuratecolony
counts(CFU)
couldbe madeforbetween102
and106(1:10 dilution)
or107(1:100dilution) CFU. Counts belowthis range(growth
in brothonly)wereclassified as less than102
CFU,
andcountsabovethis range(toonumerous to count atthe
highest dilution)
werecalled either106or107
CFU forthe twodilutions, respectively.
Organisms
werethen identifiedby
routinemicrobiologicaltechniques,
except that the coagulase-negative staphylo-cocci were not determined to thespecies
levelduring
thefirst 24 months of the study period. During the last 12
months,
107 catheter cultures grew coagulase-negativestaphylococci,
and thespecies
of allof theseorganisms
weredetermined
by using
the MicroScan Gram-Positive Combo Panel(Baxter
HealthcareCorp.,
Sacramento, Calif.). Forcoagulase-negative staphylococci,
when both blood and catheterculturesgrew thesameorganism,
theantimicrobialsusceptibility
andbiotype
data were compared to try toexclude the
possibility
ofcontamination.Blood cultures.
During
the 36-month study period, theblood culture results were reviewed for each
patient
from whomacatheter(s)
was obtained andcultured todetermineany
relationship
thatmight
exist between the twotypes of cultures. Blood cultureswereperformed by using
the BAC-TEC460system(Johnston Laboratories,
Inc.,Becton Dick-inson andCo., Cockeysville, Md.).
Because oftheretro-spective
nature of thisanalysis,
we couldnot be certain of therelationship
between the timethe catheterwasinsertedandthe time thebloodculturesweredrawn. Toincrease the
likelihood that blood culture results
might
reflect anyasso-ciated catheter
infection,
we chose to consideronly
those blood culturesthatwere drawn within 48 hprior
tocatheterremoval. This interval was selected because
virtually
all types ofvascular cathetersreported
intheliterature areleft inplace
forgreater than 48 h(6).
Clinical data collection. A
retrospective
medical chartreviewwas carriedout tolookfor clinical correlations with
the catheter culture results. We focused on non-burn
pa-tients who had
positive
catheter cultures and anassociatedblood
cultures)
withintheprevious
48 h. Burnpatients
were excludedbecause ofourinability
toestablish whetheraburnwoundinfection existed based
only
onretrospective
medical chart review.Of
106patients
who fit thesecriteria,
104(98%)
had charts available for review. Data collected for this purpose included
diagnosis,
antibiotictherapy,
documenta-tion of infecdocumenta-tions at othersites,
evidence of catheter inser-tion site infecinser-tion(erythema,
pain, tenderness,
purulence),
the type ofcatheter
inserted,
and the presence ofimmuno-suppression.
Definite infections atother locations were defined based onthe
following
criteria:aculturegrowing
asingle organism
which was the same as the bloodstream isolate and
(i)
pneumonia
documentedby
a chest X ray andphysician
evaluationplus
a sputumculture with atleast 2+(0
to4+scale) growth
on theplate, (ii)
aurinary
tract infection definedby
thegrowth
ofmore than100,000
CFU/mlfromaclean-catchurine
sample
or morethan1,000 CFU/ml
froma catheterized urinesample,
or(iii)
anintra-abdominal
infec-tiondiagnosed
by aphysician.
Data
analysis.
Colony
counts wereexpressed
asgeometric
means because ofa wide range of datumpoints.
To deter-mine whetheraquantitative relationship
existedbetween the numberoforganisms
removed from cathetersby
sonication and thefrequency
ofpositive
blood cultures for the sameorganism, catheter culture results were grouped by powers of 10(e.g., .102 to
<103, 2103
to<104).
Themeannumber oforganisms(log1,)
ineach group was calculated to be used asthe xcoordinate. For these same groups, the percentage of catheter culture isolates that had blood culturesgrowing the sameorganismwasusedasthe y coordinate. Thexand y pairs from each quantitative catheter culture group were then used to perform linear regression, which was accom-plished by a least-squares method.Predictive values for positive blood cultures were calcu-lated for the six mostcommon catheter culture isolatesby using 2 by 2 tables. Cell a contained the number of catheter cultures growing the organism in question in the high-titer range with associatedpositive blood cultures for the same organism within the previous 48 h. Cell b contained the number of catheter cultures growing the organism in ques-tion in the high-titer range with associated negative blood cultures for the organism in question. Cell c contained the
number of catheter cultures growing the organismin ques-tion in the low-titer range with associated positive blood cultures for thesameorganism within the previous 48 h. Cell d contained the number of catheter cultures growing the
organismin question in the low-titer range with associated
negative blood cultures for theorganism inquestion. Thus, thepositivepredictive valuewasequalto[(a)I(a+b)] x 100, and thenegative predictivevaluewasequalto[(d)l(c+d)] x 100.
The Student t test or Mann-Whitney rank sum test was used to analyze the quantitative culture data. Differences between proportions were tested bythe chi-square test or theFisherexact test.Allstatisticaltests weredoneby using
TrueEpistat software (Epistat Services, Richardson, Tex.)
on a microcomputer (PC XT; International Business Ma-chines).
RESULTS
Catheter cultures.Duringthe36-monthperiod, 1,681 cath-etersfrom 355patientswerecultured(Fig. 1).Burn patients
(92
[25.9%])
madeupthesingle largestgroupofpatients, and significantlymorecatheter cultureswereperformedperburnpatientthan per non-burnpatient (12.2 + 13.0versus 1.9 ± 1.7cathetercultures,respectively;P<0.0001). Thisfinding
was undoubtedly related to a burn unit protocol which specified that ail vascular catheters in burn patients be
changed (usuallyover aguidewire)atleast every 3daysand sentfor culture. Non-burnpatients weresignificantly more
likelyto have apositivecatheterculturethan burnpatients
were (292 of508 non-burn patient catheters [57.5%] versus 482 of 1,173 burn
patient
catheters[41.1%]; chi-square
=37.7;P<0.001). Inprospective studies ofvascular catheter
infections in burnpatients (10) and non-burn patients (11),
Makietal.foundthat burn
patients
haveamuchhigher
riskof catheter-related infection (16of 50 burnpatientcatheters grew greaterthan 14CFUversus25 of250 non-burn
patient
catheters;P<0.001).Thiscouldmeanthatourburnpatient populationwasdifferent from theirpatient populationorthat thefrequentchangingof catheters inourburn unitdecreased the riskof infection. Alternatively, and morelikely, it mayonly indicate that the riskofa
positive
catheterculturewashigherinournon-burnpatientsbecausethose catheterswere cultured because of
suspected
infection rather than because ofaburnunitprotocol.Therewere more cathetersfromwhicha
single organism
grew (590 catheters
[76.3%])
than from which multipleorganisms
grew. There were 184 catheters withon April 12, 2020 by guest
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355 Patents (1681 Catheters) 1681 Caihetes
92 Burn Pcatlents
~1
1173 Catheters
482 Pos 691 Neg
263 Nonbum Patlents
J1
508 Catheters
292 Pos 216 Neg
907Caiheters nogrwth
489Ccihetes
nooesockitd
kbl
bbod
culture418Caihotes had associted bboodculture
774 Caltheter
culture posmve
369Cthote noaooclated
\ 6 blood cultures 405Caihetei
hod seoëlated bboodcultures
544Caiheter Organime
220/292 Catheters
had aoclated blood cultures
In 106 poatents. Charter were avdlable for 104 patients
(216 catheters).
FIG. 1. Catheterculture results bypatient group. The box rep-resentsthe dataobtained from medical chart review.
bial cultures; in126catheter cultures twoorganismsgrew, in 43 catheter cultures three organisms grew, in 14 catheter
culturesfourorganismsgrew, and in 1 catheter culture five organisms grew. Burn patients were less likely than
non-burnpatients to have polymicrobial catheter cultures (20.7
versus 28.8%, respectively; chi-square = 6.02; P = 0.01).
One patient, a formernurse, used a syringe to self-induce bacteremias which disappeared when her vascular access was discontinued. Three of her four positive catheter cul-tures werepolymicrobial, includingtwocultures with colony countsof2105 CFU.
A total of 1,032 organisms were isolated from the 774
culture-positive catheters (Table 1). During the study 107
strains ofcoagulase-negative staphylococciweredetermined
to the species level. The frequencies of isolation were as
follows: Staphylococcus epidermidis, 77
(72.0%);
Staphylo-coccuscapitis, 21 (19.6%); Staphylococcus haemolyticus,4
(3.7%);
Staphylococcuswarneri, 4(3.7%);
andStaphylococ-TABLE 1. Frequencyof microorganism isolation from 774 sonicated catheter cultures
Organism Frequencya %
Coagulase-negative staphylococci 376 36.4
Pseudomonasaeruginosa 143 13.9
Enterococci 103 10.0
Yeasts 95 9.2
Staphylococcusaureus 60 5.8
Enterobacter species 45 4.4
Escherichia coli 40 3.9
Corynebacteriumspecies 34 3.3
Alpha-hemolytic streptococci 27 2.6
Serratia species 19 1.8
Klebsiella species 18 1.7
Bacillus species 18 1.7
Acinetobacterspecies 12 1.2
Proteusspecies 10 1.0
Other 32 3.1
aAtotal of1,032organismswereisolated.
337 Oranisms
ln br nyI 207 Organim
gmw> or* 100 cu
FIG. 2. Catheter culture results in relationshiptobloodculture results. The box represents the source of data used for linear regression analysis.
cus hominis, 1 (0.9%). The frequencies of isolation of 93
yeastisolateswere asfollows:Candidaalbicans, 65(69.9%);
Candida tropicalis, 20 (21.5%); Candida parapsilosis, 3
(3.2%); and other, 5(5.4%).
Relationship between positive catheter cultures and blood cultures. Blood cultureswere done within 48h of catheter removal in 49% (823 of 1,681) of the catheter cultures. Withinthisgroup, therisk ofablood culture
being positive
was greater if the catheter culturewas positive (292 of405
catheter cultures
[72.1%])
than if itwas negative (86 of418 catheter cultures[20.6%];
P < 0.0001). A total of 544organisms
weregrownfromthe405 catheters withpositive
cultures; for175(32.2%)
oftheseorganisms inthe catheter cultures therewere associated blood cultures thatgrewthesame organism.
Ananalysiswasdonetodetermine whether any
quantita-tive relationship existed between the number oforganisms removedby sonicatedcathetercultureand thefrequencyof associated blood cultures growing the sameorganism. The dataanalyzedcamefrom the207catheter cultures from both burn and non-burnpatients
that grew greaterthanorequalto102 CFU and that had associated blood cultures in the previous 48 h (Fig. 2). The number of catheter cultures in
each quantitative group was as follows:
102
to<103,
53cultures; 103to
<104,
54cultures;104
to<105,
34cultures;105
to <106,34cultures;106 to<107,
18 cultures; and2107,
14 cultures. The following linear regression equation was
calculated: (frequency of positive blood cultures) = 14 x
[loglo(number
ofCFU removed from the catheter)]-21(r=0.93;
r2
=88%,
adjusted for degreesof freedom). Thelinearregression
line is drawn in Fig. 3, along with the 95%confidence bands.
The
regression analysis
combined data from burn andnon-burnpatientsbecause ananalysisofeach group
individ-ually(datanotshown)demonstrated
nearly identical results.
There was nodifferencein the
regression
analysis whether thebloodcultures werepositiveonthedaythe catheterwasw
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o
0
.0 w
r-Oc
CLcm
Do
0 ,0
_-
-,sO
-£
ou
Co
mR
8
7
S LL
c4.
(3
O
2.
0
0)
c
cO
0,
-J
.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0
Log 10(QuantftativeCatheter CultureCFU)
FIG. 3. Quantitative relationship betweenthe number of
organ-ismsremovedfrom 207 catheters by sonicationand the frequency of
positive bloodculturesfor the sameorganism. The solid lineis the
linearregression line, and the dashed linesarethe95%confidence
limits.
removedor1or2days previously.Cathetercountsclassified
as<102 (positive in broth only)wereexcluded because they
could represent any catheter count between 1 and 99. Catheter culturesgrowing coagulase-negative staphylococci during the first 2 years of the study were also excluded
becausethey werenotdeterminedtothespecies level, and therefore, it could not be determined whether the blood culturewas growing thesameorganism.
Therelationship between positive blood cultures and the sixmostcommonorganisms (Table 1) isolated from catheter cultures is shown in detail in Fig. 4. The frequencies of blood culturesgrowing the sameorganisms asthe catheters were
as follows: C. albicans, 68.4%; Staphylococcus aureus,
60%; Enterobacter cloacae, 42.9%; Staphylococcus epider-midis, 32.1%; Pseudomonas aeruginosa, 27.7%; and
Strep-tococcusfaecalis, 23.3%. Catheter cultures positive for C. albicansweremorelikelytohave associated positive blood cultures than any other organism except Staphylococcus
aureus(P' 0.05). Staphylococcusaureuswas morelikelyto
have associated positive blood cultures than Staphylococcus epidermidis, P. aeruginosa, andStreptococcusfaecaliswere
(P<0.001). Catheter cultures positive for C. albicanswere
remarkable in anotherrespect. Sixty-one percent(11 of 18) of catheter culturesgrowing C. albicansin brothonlywere associated withpositive blood cultures for C. albicans (Fig. 4). This frequency was higher than that for any other
organismgroup but only statistically higher than those for Staphylococcus epidermidis,P.aeruginosa,and
Streptococ-cusfaecalis (P c 0.03).
For these same six organisms, predictive values of
posi-tive andnegative catheter culture results forapositive blood
culture with the same organism were calculated (Tables 2
and 3). For C. albicans and Staphylococcus aureus, the
predictive values ofapositive catheter culturewere -60%,
no matterhowmany CFUgrewfrom thecatheter, whereas for the other fourorganisms the predictive values did not reach this level until at least 105 CFU were grown. The predictive value ofatotally negativetestwasexcellent for all
six organisms (.98%). For positive catheter cultures the negativepredictive value didnotvarymuch, ranging from 57
to 87% for E. cloacae, P.aeruginosa, Streptococcus faeca-lis, and Staphylococcus epidermidis and from 37to57%for Staphylococcusaureusand C. albicans.
For cathetercultures thatwerepositive in broth only (223
of405), blood culturesthatgrewthesameorganismoccurred
6
5
4
3~
2
1
_. 0
o
-X
. ~ ~~
- -r , D
*D0 0 3~~~ O O
Ô
aC
COD* O o O CD
-æ*:
___
- -
s
m
s
tB°~~~
8 ~ r mm
CD
be .e . e o
FIG. 4. Relationship between positive blood cultures and the numberoforganismsremovedfrom cathetersbysonication forthe
six mostcommon organisms causingvascular catheter infections. Symbols:*,positive bloodcullture for thesameorganismdone in the 48hbefore the catheterculture; O,negativeblood culture for the cathetercultureorganisminthe 48 h before the catheter culture.
frequently (non-burn patients,
20 of 70 catheter cultures[28.6%];
burnpatients,
42of 153 cathetercultures[27.4%]).
Thisratewassimilarfor blood cultures that grew
organisms
that were different from those that grew in the catheter cultures
(non-burn
patients,
13of 70 blood cultures[18.6%];
burn
patients,
27 of 153 blood cultures[17.6%])
and for catheter cultures in which there was nogrowth (non-burn
patients,
16of 75 catheter cultures[21.3%];
burnpatients,
63 of 331 catheter cultures[19.0%]).
Thesefindings
collectively
suggestthat manyofthesepositive
blood cultures may have littletodo with the vascular catheter.Seventeencatheter cultures grew
Staphylococcus
epider-midis and had associated
positive
blood cultures for acoagulase-negative staphylococcus (Fig. 4).
Susceptibility
testing
andbiotyping (MicroScan)
wereperformed
forall'17catheterculture
isolates,
but bothwereperformed
foronly
9TABLE 2. Predictive values ofpositivesonicatedvascular catheter cultures forpositivebloodcultures
Predictive value(%)for thefollowing Organism cathetercultureresults:
>° _102 103 2104 2W
Candida albicans 68.4 75.0 81.8 81.8 80.0 Staphylococcusaureus 60.0 69.2 68.2 77.8 80.0 Staphylococcus epider- 32.1 37.5 44.4 66.7 66.7
midis
Streptococcusfaecalis 23.3 41.2 36.4 36.4 37.5 Pseudomonasaerugi- 27.7 31.3 43.5 43.8 63.6
nosa
Enterobacter cloacae 42.9 50.0 45.5 42.9 60.0
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TABLE 3. Predictivevaluesofnegative sonicatedvascular catheterculturesforpositivebloodcultures
Predictive value(%)for thefollowingcatheter Organism cultureresults:
>0 .102 103 i104 .io5 Candida albicans 98.8 38.9 37.0 37.0 35.7 Staphylococcus 99.3 57.1 50.0 54.5 52.0
aureus
Staphylococcus 99.3 72.4 74.3 75.0 70.0 epidermidis
Streptococcus 98.4 86.7 76.2 73.6 73.2 faecalis
Pseudomonas 98.7 75.8 81.0 77.6 79.6
aeruginosa
Enterobacter clo- 99.4 66.7 60.0 57.1 60.0 acae
of theblood culture isolates. For the nine pairs of organisms (catheter culture and blood culture) for which both
suscep-tibilities and biotypes wereavailable, five pairswere
identi-cal (differing by <1 antibiotic susceptibility orbiotype) and
four pairs were different. For the five identical pairs, the
mean quantitative catheter culture result was 4.4 ± 1.9
(standard deviation) versus2.2 ± 0.6CFU for the others (P
= 0.06by the Student ttest). This suggeststhat when low numbers of Staphylococcus epidermidiswereremoved from
the catheter by sonication and the associated blood culture
was positive for Staphylococcus epidermidis, one or the
otherisolate waslikelytobea contaminant.
Clinicalcorrelations. The medical charts of 104 non-burn patients with 216 positive catheter cultures were reviewed (Fig. 1). The most common underlying medical problems weretrauma (13.5%) and cancer(13.5%). Seventy-two
per-centof thesepatients resided inanintensivecareunitatthe timeoftheir catheter infection(s); theyweremostcommonly on a general surgery (26.9%), pediatric (25%), or general
medicine (21.2%) service. Eight of the patients died during theirhospitalization. Immunosuppression wasrelatively
in-frequent, exceptfor theuseof steroids(17.3%). Thetypeof catheter used wasrecordedtooinfrequently toprovide any
usefuldata.
Of the 216 positive catheter cultures evaluated in the medical chart review, 24grew <102CFU (positive in broth
only) and had associated positive blood cultures for thesame
organism. Of these 24 catheter cultures, 11 (45.8%) were
associated with another definite site of infection with the same organism compared with 5 of 73 catheter cultures (6.8%; P< 0.0001by the Fisherexacttest) thatgrew >102
CFU.Of these 11 infections, 6wereendovascular in location (5werefrom other vascular catheters and1wasfroma case
of endocarditis) and 4 were urinary tract infections (all caused by C. albicans). Furthermore, for catheter cultures that were positive in broth only and that were associated
with negative blood cultures or blood cultures that grew
different organisms from the catheter, the incidence of a
documented infection caused by thesame organism asthat
isolated from the catheterwas much lower (12.1% [8 of 66
cathetercultures];P=0.001by the Fisherexacttest).These
data suggest that the true incidence of positive blood cul-tures caused by catheters with low numbers of organisms (i.e., in broth only)was verylow (probably <15%).
Although there was a very strong correlation between positive blood cultures for the catheter organism and the number of colonies removed from the catheter by sonica-tion, itwaspossible that antibioticuse mayhaveresultedin
TABLE 4. Clinicalfindings in non-burnpatientsassociated with vascularcatheter cultures
No.of catheter cultureswith theassociated clinicalfindings:
Organism Definite Catheter
Total +BC- othersite site Fever
infections purulence
Staphylococcus 15 12 0 6 12
aureus
Candida albicans 13 9 5 0 il
Enterobacterclo- il 6 2 3 9
acae
Staphylococcus 28 9 2 1 21
epidermidis
Pseudomonas 22 6 8 1 18
aeruginosa
Streptococcus 24 5 2 5 18
faecalis
aBlood cultures positive (+BC) for thesame organism as thecatheter
culture.
bInfection with the same organismat a site distant from the vascular
catheter.
false-negativeblood cultures.Of the catheter cultures which grew2105colonies(53of 216 cathetercultures), only1of 20 catheters with negative blood cultures was associated with antibiotic therapycompared with 13 of 26 (P = 0.001 by the
Fisherexact test) ifthe blood culture was positive for the sameorganismasthe catheter and 4of7if thebloodculture waspositivebutforadifferentorganism. Antibiotics
appar-ently were used because the patient had a positive blood
culture, appeared ill, or both and did not result in
false-negative bloodcultures.
We next focused on whether there were any clinical
findings that were unique to specific organisms. These re-sults are summarized in Table 4. For the three organisms that are the most common causes of catheter infections
reported in the literature (6) (Staphylococcus epidermidis,
Staphylococcus aureus, and C. albicans), there were two
interesting findings. Purulenceatthe catheterinsertion site was documented in the chart with 40% of Staphylococcus aureus catheter infections, a frequency which was signifi-cantly higher than that for purulence associated with C. albicans or Staphylococcus epidermidis infections (P <
0.05). C. albicans was more likely than the other two
organismstobeassociated withadefinitecauseof infection
at asite distantfrom the catheter(Ps 0.05).Thesefindings
must be viewed with caution because ofthe retrospective
mannerinwhichthese data wereobtained.
DISCUSSION
Useof theroll-plate methodforculturing vascular cathe-ters has greatly improved ourunderstanding ofthe
patho-genesis of vascular catheter infections (11). By using this
technique,it has beenpossibleto show associations between
colonization oftheskin and the number oforganisms on the catheter(19) and between thenumber oforganisms on the catheter andinsertion siteinflammation, insertionsite puru-lence, and catheter-related bacteremia (or fungemia) (11). As aresult, theconcept has been advanced that the majorityof vascular access infections develop because of organism
multiplicationattheinsertion site, withsubsequent multipli-cation around the catheter in the subcutaneous space and thenthe bloodstream(11).
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However, theroll-plate technique is capable of enumerat-ing fewer than 1,000 organisms; catheter cultures growing more than 1,000 CFU are lumped into a category of 103
organisms (11). Notably, in the original study of Maki et al. (11), in all four cases of catheter-related bacteremia quanti-tative catheter cultures grew-103organisms, but so did nine other catheter cultures obtained from patients withno asso-ciated bacteremia. This observation suggests that useful information could beobtained if theupperlimit of quantita-tion could be extended. Cleri et al. (3) studied this by
flushingthe lumenof the catheter three times with broth and doing serial dilutions. Fordifferent ranges ofcatheter organ-ism counts, they found the followingfrequencies of catheter-relatedbacteremia: <103, 0%;
103
to104, 28.6%(2of 7); 104to106,50% (6 of 12); >106, 100% (5 of 5). Bjornson et al. (2) have reported similarresults with acentrifugationtechnique followed by serial dilutions:
<103
organisms per catheter, 14.3% (2 of 14); 103to105,
55.6%(5 of 9);>i05, 100% (3 of3).
In aprevious prospective study ofSwan-Ganz catheters,
wefound that the sonication method for culturing vascular
catheters demonstrated an association between
catheter-related bacteremia and the number oforganisms removed from Swan-Ganz catheters (7). Forfour ofthe five catheters that were associated with catheter-related bacteremia, vas-cular catheter cultures grew greater than 103 organisms. Similarobservations havebeen made by otherinvestigators
who used the roll-plate method (12, 16). The present study solidifies the quantitative relationship between the number
oforganisms removed from avascular catheter by sonication and the incidence of bacteremia. Among the 207 catheter
cultures that grew .102 CFU and had an associated blood culture within 48 h prior to catheter removal, there was a correlation of 0.93 (r2 = 0.88) between the frequency of concordantpositivebloodcultures and the number of organ-isms recovered after sonication. These findings may mean that the number of organisms on the catheter represent
different points in time on the natural history curve for the
infection. Thus, likeurinarytract infections associated with bladder catheters, small numbers oforganisms may repre-sent earlystages ofinfection and largenumbers may repre-sent late stages ofinfection (20). This very strong
quantita-tive correlation also raises the possibility that the quantitation oforganisms in clinical microbiology
laborato-ries may help to discriminate between catheter-related pos-itive bloodculturesandbacteremiasorfungemiasfrom other sources. Furtherprospective investigationsarenecessary to address these considerations.
The most remarkable findings of this study were the strikingdifferences betweenthe microorganismsthatcaused
infection. While coagulase-negative staphylococci were the mostcommonisolates from vascularcatheters, these organ-isms, and Staphylococcus epidermidis in particular, were much less likely to have anassociatedpositive blood culture than Staphylococcus aureus and C. albicans were. This study provides the first hard data supporting the long-held
clinical impressions that Staphylococcus aureus and C.
albicans are unique causes of vascular access infections.
Catheter cultures growing Staphylococcus aureus had
sta-tistically higher catheter culture counts and a greater fre-quency ofassociated positive blood cultures than did cath-eter cultures growing any other organism group except the yeasts. Retrospectively, with Staphylococcus aureus infec-tions there was a greater frequency of purulence at the
catheterinsertion site and very little evidence of infectionsat other sites contributing to the process. This implies that
Staphylococcus aureus mayhave unique virulence charac-teristics that facilitate its growth in the environment sur-rounding the vascular catheter.
With C. albicans, as with Staphylococcus aureus, there was a high frequency of positive blood cultures associated
withcatheter cultures that grew greater than102 CFU (15of
20 cathetercultures [75%]); there was little evidence of C.
albicans infections at other sites (1 of8 catheter cultures [12.5%]). However, there was also a very high frequency of blood cultures positive for C. albicans associated with
catheter cultures that grew less than 102 CFU (11 of 18
[61%]), in conjunctionwithahighfrequencyof documented othersitesof infection(4of5 inthemedicalchartreview; P = 0.03 in comparison with >102 C. albicans by theFisher exact test). Bjornson et al. (2) found that a
significant
percentage ofpatients with C. albicans vascular infections
had no C. albicans detectable on the skin at the site of
catheter entry, raising the possibility that C. albicans reaches the catheter by a source otherthan theskin. Given the known ability of C. albicans to stick to fibrin and platelet matrices (9) andfibronectin (17), thissuggests thepossibility of hematogenous seeding of the catheters (14). Thus, the sonicated culture technique, by expanding the range of quantitation, can categorize organisms into groups that
suggest differences in the pathogenesis ofinfection.
The high positive predictive values for catheter-associated positive blood cultures (.60 to 80%) calculated for C.
albicans and Staphylococcus aureus strongly suggest that
catheters growing any titer of either of these organisms
should be considered infected and to contribute to the positive blood culture. The much lower positive predictive
values for Staphylococcus epidermidis, Streptococcus faecalis, and P. aeruginosa, when less than 102 of these
organisms were removed (23 to 32%), suggest that ahigher
cutoff value (>102 CFU) should be used to define catheter-related bacteremia. This was shown quite well when both catheters and bloodcultures grewStaphylococcus epidermi-dis; forcathetercultures withless than 102CFU, only one of four isolates had the same biotype and susceptibility as the bloodstream isolate versusfour of five isolates if the cathe-ters grew greater than 102 CFU. E. cloacae fell between these two groups of organisms, and it is not clear how it should be handled.
In conclusion, sonication is an effective means of remov-ing organisms from vascular catheters. It greatly increases the number oforganisms thatcan bequantitated, in compar-ison with the roll-plate technique. The close relationship
between the number of organisms removed and the risk of bacteremia in theprevious 48 h suggeststhat itmay be very useful in clinical microbiology laboratories. Perhaps the most important finding was that this technique provides
sufficient resolution to distinguish differences between or-ganisms in theirability to cause vascular access infections.
Further prospective investigations are indicated to explore
thepotentialof this method forculturing vascular catheters.
LITERATURE CITED
1. Adam, R. D., L. D. Edwards, C. C.Becker, andH. M. Schrom.
1982. Semiquantitative cultures and routine tip cultures on
umbilical catheters. Pediatrics 100:123-126.
2. Bjornson, H. S., R. Colley, R. H. Bower, V. P. Duty, J. T. Schwartz-Fulton, andJ. E. Fischer. 1982. Association between microorganism growth at the catheter insertion site and coloni-zation of the catheter in patients receiving total parenteral nutrition. Surgery 92:720-726.
3. Cleri, D. J., M. L. Corrado, and S. J. Seligman. 1980. Quanti-tative culture of intravenous catheters and other intravascular
on April 12, 2020 by guest
http://jcm.asm.org/
inserts. J. Infect. Dis. 141:781-786.
4. Collignon, P., R. M. Chan, and R. Munroe. 1987.Rapid diag-nosis of intravascular catheter-related sepsis. Arch. Intern. Med. 147:1609-1612.
5. Collignon, P. J., N. Soni, I. Y. Pearson, W. P. Woods, R. Munro, and T. C. Sorrell. 1986. Is semiquantitative culture of central vein catheter tips useful in the diagnosis of catheter-associated bacteremia?J. Clin. Microbiol. 24:532-535.
6. Hampton, A. A., and R. J. Sherertz. 1988. Vascular-access infections in hospitalized patients. Surg. Clin. North Am. 68: 57-71.
7. Heard,S. O., R. F. Davis, R. J. Sherertz, M. S. Mikhail, R. C. Gallagher, A. J. Layon, and T. J.Gallagher. 1987. Influence of sterile protective sleeves onthe sterility of pulmonary artery catheters. Crit. Care Med. 15:499-502.
8. Linares, J., A. Sitges-Serra, J. Garau, J. L. Perez, and R. Martin. 1985. Pathogenesis of catheter sepsis: a prospective study with quantitative andsemiquantitative cultures on cathe-terhub and segments. J.Clin. Microbiol.21:357-360.
9. Maisch, P. A., and R. A. Calderone. 1980. Adherence of Candida albicans to a fibrin-platet matrix formed in vitro. Infect. Immun. 27:650-656.
10. Maki, D. G., F. Garrett, and H. W.Sarafin. 1977. A semiquan-titativemethod foridentification of catheter-relatedinfection in the burn patient.J. Surg. Res. 22:513-520.
11. Maki, D. G., C. E. Weise, and H. W.Sarafin. 1977. A semiquan-titative culture method for identifying intravenous-catheter-relatedinfection. N. Engl. J.Med. 296:1305-1309.
12. Meyers, M. L., T. W. Austin, and W. J. Sibbald. 1985.
Pulmo-nary arterycatheterinfections. Aprospective study.Ann.Surg. 201:237-241.
13. Moyer, M. A., L. D. Edwards, and L. Farley.1983. Comparative culture methods on 101 intravenous catheters. Arch. Intern. Med. 143:66-69.
14. Rotrosen, D., R. A. Calderone, and J. E. Edwards. 1986. Adherence of Candida species to host tissues and plastic surfaces. Rev. Infect. Dis. 8:73-85.
15. Sherertz, R. J., R. J. Falk, K. A.Huffman, C. A. Thomann, and W. D. Mattern. 1983. Infections associated with subclavian Uldall catheters. Arch. Intern. Med. 143:52-56.
16. Singh, S., N. Nelson, I.Acosta, F. E. Check, and V. K. Puri. 1982.Catheter colonizationand bacteremia withpulmonary and arterial catheters. Crit.Care Med. 10:736-739.
17. Skerl, K. G., R. A. Calderone, E. Segal, T. Sreevalsan, and W. M. Scheld.1984.Invitrobinding of Candida albicans yeast cells to humanfibronectin. Can.J. Microbiol.30:221-227. 18. Snydman, D. R., S. A. Murray, S. J. Kornfield, J. A.Majka,and
C. A. Ellis. 1982. Total parenteral nutrition-relatedinfections. Prospective epidemiologic study using semiquantitative meth-ods.Am.J. Med.73:695-699.
19. Snydman, D. R., B. R. Pober, S. A. Murray, H. F. Gorbea, J. A. Majka, and L. K. Perry. 1982.Predictive value of surveillance skin culturesintotal-parenteral-nutrition-relatedinfection. Lan-cetii:1385-1388.
20. Stark, R. P., and D. G. Maki. 1984.Bacteriuria inthe catheter-izedpatient. What quantitative level of bacteriuriais relevant? N.Engl.J. Med. 311:560-564.