INFECTION
Diagnosis
of
Urinary Tract
Infection
The Interpretation of Colony Counts David A. Slosky, M.D.,* James
K.
Todd, M.D.†
The results of 787 consecutive suprapubic specimens in children were studied. Ninety-two patients with 128 positive cultures were reviewed. Sixtyfive children had documented urinary tract infection (UTI) proven by other cultures. Of these, 55 per cent had colony counts less than the traditional 100,000 colony forming units/ml., and 9 per cent had colony counts less than
10,000. Organisms usually regarded as "contaminants" (Staphylococcus epidermidis, mixed organisms) were occasionally proven to cause UTI.
THE fection (UTI)
DIAGNOSIS of
urinary tract inin children requires laboratory documentation of the persistence of bacteria in what normally is a sterile urinary _
Since bacterial contamination can during the urine collection process, strict criteria for the interpretation of quantitative culture results must be established to prevent the consequences of overdiagnosis (unwarranted expense, medication, irradiation, or surgery), and also of underdiagnosis (progressive renal disease due to infection). This study deals with the results of 787 suprapubic urine cultures in children and apples them to previously described diagnostic criteria. tract.
occur
From: The Department of Pediatrics, University of Colorado Medical Center, and the Children’s Hospital of Denver, Denver, Colorado. * Department of Medicine, Duke University, School of Medicine, Durham, North Carolina. t The Children’s Hospital, 1056 E. Nineteenth Ave., Denver, Colorado 80218. Correspondence to: James K. Todd, M.D., The Children’s Hospital, 1056 E. Nineteenth tlve,, Denver,
CO 802 IS.
Materials and Methods The
patients selected for this retrospective study were all children who had a suprapubic bladder aspiration at Colorado General Hospital between January, 1971, and June, 1973. The indications for the suprapubic bladder aspirations were: child severely ill, had had equivocal culture results with other collection methods, had a structural or functional urinary tract abnormality, or was a newborn with suspected septicemia. The urine specimens were quantitatively streaked with a 0.01 ml loop and plated on blood and l~IacConkey agar. This method permits accurate enumeration between 100 and 10,000 colony forming units/ ml; counts greater than 10,000 colony forming units/ml are estimated. During the study period, 787 suprapubic urine cultures were done; of these, 659 were sterile. There were 92 children with 1 . suprapubic cultures which had bacterial growth. Patients were listed as being in the &dquo;documented infection&dquo; group when a second positive suprapubic culture grew the
sheep
698
Downloaded from cpj.sagepub.com at Purdue University on June 14, 2015
FIG. 1 Distribution «f~ cases as
comparedtodocu-
mcntation of infection and
colony
count.
organism, or a dean voided or catheterized specimen had greater than 100,000 colonies per ml of the same organism. The &dquo;no infection&dquo; group was defined as those patients who had a second clean-catch midstream specimen, or a catheterized or a suprapubic culture which did not grow the same organism, or was sterile. Of patients with a single positive suprapubic culture 44 per cent did not have repeat cultures and were tabulated as &dquo;suspected infection.&dquo; same
fection&dquo;). Thirty (46 per cent) of the 65 children studied with documented urinary tract infections had colony counts between 10,000 and 100,000 colony forming units/ml of urine, and 6 (9 per cent) had colony counts less than 10,000 colony forming units/ml. Three of these 6 patients with colony counts less than 100,000 colony forming units/ml were being treated with antibiotics, which may have suppressed organism growth, and one additional child had recent
urinary
surgery (cutaneous culcounts less than 10,000
tract
ureterostomy). Of the 12 suprapubic
Results Table I demonstrates the age and sex distribution of the 92 children with 128 positive suprapubic cultures. The numbers of positive cultures and the numbers of documented infections were similar for each age division. As has been previously noted, the infant, pre-school, and school-age infections occurred primarily in girl, whereas in the newborn, the boys predominated. Figure I shows the distribution of quantitative culture results and their relation to 65 documented infections and 6 false positive cultures (&dquo;no in-
tures
with
TABLE 1.
colony
Aae and Sex Z3istribiation nf G’h~lt~ren ‘
Confirmed
witli
Citltzcre Re,5ult5
699
Downloaded from cpj.sagepub.com at Purdue University on June 14, 2015
TABLE 2.
C~M/WMM r~ f)r~rtnis’rrzs aH~Cc~K~
Cotints iri l’~cttr·rits 7i,ith
C~M/!’rm~
L&dquo;rine Ciilttire Resz~d~s
* No tnf’ection~-initial culture result not confirmed by subsequent cultures. t Infectic~ri-initial culture result confirmed by subsequent cultures.
Pyuria is often seen in children with febrile illnesses unassociated with urinary tract infection and is absent in almost 50 per cent of those with significant bacteriuria.&dquo; The economic and medical consequences of overdiagnosis of UTI may be very signifyicant, as children may be subjected to needless antibiotic usage, office visits, radiologic procedures, urologic manipulation, and surgery. Thus, Kunin~ and Stamey,~ in two recent books on UTI, emphasize the concept that the diagnosis of UTI should always be
colony forming unit~lml, 6 proved to be false positive results, in that subsequent cultures and other findings did not document infection. In contrast, no instances with colony counts greater than 10,000 colony forming units/ml could be shown
to
be
tracts.
erroneous.
Organisms traditionally assumed to be contaminants (Staphylococcus epidermidis-4 patients, and diptheroicls---I patient) were usually associated with low colony counts and &dquo;no infection&dquo; (Table 2), though two boys had documented urinary tract infections caused by ,S. ~ e~rcderrrc~dis with colony counts greater than 100,000 colony forming units/ml. Also, contrary to commonly accepted diagnostic criteria, seven infections (11I per cent) could be documented to be caused by mixed bacterial species (more than one organism). Five of these children had significant urinary tract abnormalities (ureteropyelocaliectasis-4 ; renal transplant-I). Discussion
According to a recent survey,~ a majority of pediatricians and family physicians accept a history of symptoms of dysuria associated with pyuria as being diagnostic of urinary tract infection. Kunin6 has demonstrated that many children with significant UTI resulting in renal scarring may remain asymptomatic, and Kbhlerl has shown that most children with &dquo;classic&dquo; UTI symptoms (dysuria, increased frequency) have sterile urinary
based
‘
positive urine culture, growing than 100,000 colony forming units/ml greater on at least two separate cultures, when the clean-catch midstream technique is used. Multiple cultures are needed to rule out the 7 to 12 per ceno,’ of patients whose bladder urine is sterile but who give a urine specimen significantly contaminated by the perineal flora, even when collected in a conscientious manner by a trained and competent nurse. Bag urine specimens are even less reliable.’ Thus, the traditional 100,000 colony forming ~.znitslml cutoff point has been selected, not because patients do not have urinary tract infections with colony counts less than 100,000 colony forming units/ml, but because this number helps to reduce the incidence of false positive results due to perineal contamination of the urine specimen.’ Pryles8. has demonstrated that most normal patients with urinary tract infections will on a
700
Downloaded from cpj.sagepub.com at Purdue University on June 14, 2015
‘
have
extremely high urine colony counts (greater than 1,000,000 colony forming units/ml) in concentrated first morning urine specimens but, during the day, with fluid diuresis and frequent voiding, the colony counts may often fall below 100,000 colony forming units/ml. Thus, physicians relying on a colony count of greater than 100,000 to establish the colony forming units/ml diagnosis of urinary tract infection, although more accurate than those who rely on no culture at all, may still miss infection if random, rather than first-morning concentrated urine specimens are cultured. In adults, this false
negative
rate
may be
as
high
as
28
per cent.3 In the present series, 55 per cent c~f’ children with urinary tract infection documented by suprapubic aspiration of the bladder had colony counts less than the traditional 100,t~4~ colony forming units/ml, and 9 per cent had colony counts less than 10,000 colony forming units/ml. Eleven percent had documented infection with mixed organisms, and two others grew ~S. e~iderrnir~as, which, had they been noted on a clean-catch midstream specimen, might have been disregarded as due to contamination. To adequately ensure minimization of errors in the diagnosis of urinary tract infection, children in screening programs, or with mild signs and symptoms possibly related to the urinary tract, should have concentrated urine
specimens cultured to ensure adequate diagnosis. Random specimens, other than firstmorning concentrated specimens, which grow less than 100,000 colony forming units/ml may still be associated with true infection. Clean-catch midstream cultures growing greater than 100,000 colony forming units/r~l should always be repeated to confirm infection, as contamination, even at these high
les-els, may be frequent.:J,6 Mixed cultures, and specimens growing S. e¡Jidennidis, cannot necessarily be assumed to be due to contamination, especially in boys and children with urinary tract abnormalities. Children with moderate-to-severe clinical signs and symptoms’ for whom immediate diagnosis and therapy are needed should have tests of a suprapubic or catheter obtained urine.’ Those who have true infection with colony counts less than 100,000 colonies per ml will not be o~~ez-loc~~ed, and those who do not have urinary tract infections but who would have a clean-catcli midstream urine specimen contaminated with greater than 100,000 colonies per ml will be eliminated. References 1.
Boehm, J. J., and Haynes, J. L.: "midstream
catch" urines. Am. J.
Bacteriology of Dis. Child 111:
366, 1966.
T. F., and Meyers, A.: Survey of management of urinary tract infections in
2. Dolan,
office child-
3.
hood. Pediatrics 52: 21, 1973. .: Diagnosis of urinary tract Dove, G. A., et al infections in general practice. Lancet 2: 1281,
4.
Kass, E.
1972.
of the
H.: Bacteriuria and diagnosis of infection urinary tract. Arch. Intern. Med. 100:
709, 1957.
Köhler, L., Fritz, H., and Schersten, B.: Health control of the four-year-old child: A study of bacteriuria. Acta Paediatr. Scand. 61: 289, 1972. 6. Kunin, C. M., Southhall, I., and Paquin, A. J.:
5.
Epidemiology of urinary
tract infections. N.
Engl.
Med. 817, 1960. J. 263: 7.
—:
Detection, Prevention, and Management of Tract Infections. Philadelphia, Lee &
Urinary
Febiger, 8.
1972.
Pryles, C. V., and Lustik, B.: Laboratory diagnosis of urinary tract infections. Pediatr. Clin. North Am. 18: 233, 1971.
9.—: Comparative study of urine obtained from children by percutaneous suprapubic aspirations of the bladder and by catheter. Pediatrics 24: 938, 1959. 10. Stamey, T.: Urinary Tract Infections. Baltimore, Williams and Wilkins, 1972.
701
Downloaded from cpj.sagepub.com at Purdue University on June 14, 2015
Diagnosis
of
Urinary Tract
Infection
The Interpretation of Colony Counts David A. Slosky, M.D.,* James
K.
Todd, M.D.†
The results of 787 consecutive suprapubic specimens in children were studied. Ninety-two patients with 128 positive cultures were reviewed. Sixtyfive children had documented urinary tract infection (UTI) proven by other cultures. Of these, 55 per cent had colony counts less than the traditional 100,000 colony forming units/ml., and 9 per cent had colony counts less than
10,000. Organisms usually regarded as "contaminants" (Staphylococcus epidermidis, mixed organisms) were occasionally proven to cause UTI.
THE fection (UTI)
DIAGNOSIS of
urinary tract inin children requires laboratory documentation of the persistence of bacteria in what normally is a sterile urinary _
Since bacterial contamination can during the urine collection process, strict criteria for the interpretation of quantitative culture results must be established to prevent the consequences of overdiagnosis (unwarranted expense, medication, irradiation, or surgery), and also of underdiagnosis (progressive renal disease due to infection). This study deals with the results of 787 suprapubic urine cultures in children and apples them to previously described diagnostic criteria. tract.
occur
From: The Department of Pediatrics, University of Colorado Medical Center, and the Children’s Hospital of Denver, Denver, Colorado. * Department of Medicine, Duke University, School of Medicine, Durham, North Carolina. t The Children’s Hospital, 1056 E. Nineteenth Ave., Denver, Colorado 80218. Correspondence to: James K. Todd, M.D., The Children’s Hospital, 1056 E. Nineteenth tlve,, Denver,
CO 802 IS.
Materials and Methods The
patients selected for this retrospective study were all children who had a suprapubic bladder aspiration at Colorado General Hospital between January, 1971, and June, 1973. The indications for the suprapubic bladder aspirations were: child severely ill, had had equivocal culture results with other collection methods, had a structural or functional urinary tract abnormality, or was a newborn with suspected septicemia. The urine specimens were quantitatively streaked with a 0.01 ml loop and plated on blood and l~IacConkey agar. This method permits accurate enumeration between 100 and 10,000 colony forming units/ ml; counts greater than 10,000 colony forming units/ml are estimated. During the study period, 787 suprapubic urine cultures were done; of these, 659 were sterile. There were 92 children with 1 . suprapubic cultures which had bacterial growth. Patients were listed as being in the &dquo;documented infection&dquo; group when a second positive suprapubic culture grew the
sheep
698
Downloaded from cpj.sagepub.com at Purdue University on June 14, 2015
FIG. 1 Distribution «f~ cases as
comparedtodocu-
mcntation of infection and
colony
count.
organism, or a dean voided or catheterized specimen had greater than 100,000 colonies per ml of the same organism. The &dquo;no infection&dquo; group was defined as those patients who had a second clean-catch midstream specimen, or a catheterized or a suprapubic culture which did not grow the same organism, or was sterile. Of patients with a single positive suprapubic culture 44 per cent did not have repeat cultures and were tabulated as &dquo;suspected infection.&dquo; same
fection&dquo;). Thirty (46 per cent) of the 65 children studied with documented urinary tract infections had colony counts between 10,000 and 100,000 colony forming units/ml of urine, and 6 (9 per cent) had colony counts less than 10,000 colony forming units/ml. Three of these 6 patients with colony counts less than 100,000 colony forming units/ml were being treated with antibiotics, which may have suppressed organism growth, and one additional child had recent
urinary
surgery (cutaneous culcounts less than 10,000
tract
ureterostomy). Of the 12 suprapubic
Results Table I demonstrates the age and sex distribution of the 92 children with 128 positive suprapubic cultures. The numbers of positive cultures and the numbers of documented infections were similar for each age division. As has been previously noted, the infant, pre-school, and school-age infections occurred primarily in girl, whereas in the newborn, the boys predominated. Figure I shows the distribution of quantitative culture results and their relation to 65 documented infections and 6 false positive cultures (&dquo;no in-
tures
with
TABLE 1.
colony
Aae and Sex Z3istribiation nf G’h~lt~ren ‘
Confirmed
witli
Citltzcre Re,5ult5
699
Downloaded from cpj.sagepub.com at Purdue University on June 14, 2015
TABLE 2.
C~M/WMM r~ f)r~rtnis’rrzs aH~Cc~K~
Cotints iri l’~cttr·rits 7i,ith
C~M/!’rm~
L&dquo;rine Ciilttire Resz~d~s
* No tnf’ection~-initial culture result not confirmed by subsequent cultures. t Infectic~ri-initial culture result confirmed by subsequent cultures.
Pyuria is often seen in children with febrile illnesses unassociated with urinary tract infection and is absent in almost 50 per cent of those with significant bacteriuria.&dquo; The economic and medical consequences of overdiagnosis of UTI may be very signifyicant, as children may be subjected to needless antibiotic usage, office visits, radiologic procedures, urologic manipulation, and surgery. Thus, Kunin~ and Stamey,~ in two recent books on UTI, emphasize the concept that the diagnosis of UTI should always be
colony forming unit~lml, 6 proved to be false positive results, in that subsequent cultures and other findings did not document infection. In contrast, no instances with colony counts greater than 10,000 colony forming units/ml could be shown
to
be
tracts.
erroneous.
Organisms traditionally assumed to be contaminants (Staphylococcus epidermidis-4 patients, and diptheroicls---I patient) were usually associated with low colony counts and &dquo;no infection&dquo; (Table 2), though two boys had documented urinary tract infections caused by ,S. ~ e~rcderrrc~dis with colony counts greater than 100,000 colony forming units/ml. Also, contrary to commonly accepted diagnostic criteria, seven infections (11I per cent) could be documented to be caused by mixed bacterial species (more than one organism). Five of these children had significant urinary tract abnormalities (ureteropyelocaliectasis-4 ; renal transplant-I). Discussion
According to a recent survey,~ a majority of pediatricians and family physicians accept a history of symptoms of dysuria associated with pyuria as being diagnostic of urinary tract infection. Kunin6 has demonstrated that many children with significant UTI resulting in renal scarring may remain asymptomatic, and Kbhlerl has shown that most children with &dquo;classic&dquo; UTI symptoms (dysuria, increased frequency) have sterile urinary
based
‘
positive urine culture, growing than 100,000 colony forming units/ml greater on at least two separate cultures, when the clean-catch midstream technique is used. Multiple cultures are needed to rule out the 7 to 12 per ceno,’ of patients whose bladder urine is sterile but who give a urine specimen significantly contaminated by the perineal flora, even when collected in a conscientious manner by a trained and competent nurse. Bag urine specimens are even less reliable.’ Thus, the traditional 100,000 colony forming ~.znitslml cutoff point has been selected, not because patients do not have urinary tract infections with colony counts less than 100,000 colony forming units/ml, but because this number helps to reduce the incidence of false positive results due to perineal contamination of the urine specimen.’ Pryles8. has demonstrated that most normal patients with urinary tract infections will on a
700
Downloaded from cpj.sagepub.com at Purdue University on June 14, 2015
‘
have
extremely high urine colony counts (greater than 1,000,000 colony forming units/ml) in concentrated first morning urine specimens but, during the day, with fluid diuresis and frequent voiding, the colony counts may often fall below 100,000 colony forming units/ml. Thus, physicians relying on a colony count of greater than 100,000 to establish the colony forming units/ml diagnosis of urinary tract infection, although more accurate than those who rely on no culture at all, may still miss infection if random, rather than first-morning concentrated urine specimens are cultured. In adults, this false
negative
rate
may be
as
high
as
28
per cent.3 In the present series, 55 per cent c~f’ children with urinary tract infection documented by suprapubic aspiration of the bladder had colony counts less than the traditional 100,t~4~ colony forming units/ml, and 9 per cent had colony counts less than 10,000 colony forming units/ml. Eleven percent had documented infection with mixed organisms, and two others grew ~S. e~iderrnir~as, which, had they been noted on a clean-catch midstream specimen, might have been disregarded as due to contamination. To adequately ensure minimization of errors in the diagnosis of urinary tract infection, children in screening programs, or with mild signs and symptoms possibly related to the urinary tract, should have concentrated urine
specimens cultured to ensure adequate diagnosis. Random specimens, other than firstmorning concentrated specimens, which grow less than 100,000 colony forming units/ml may still be associated with true infection. Clean-catch midstream cultures growing greater than 100,000 colony forming units/r~l should always be repeated to confirm infection, as contamination, even at these high
les-els, may be frequent.:J,6 Mixed cultures, and specimens growing S. e¡Jidennidis, cannot necessarily be assumed to be due to contamination, especially in boys and children with urinary tract abnormalities. Children with moderate-to-severe clinical signs and symptoms’ for whom immediate diagnosis and therapy are needed should have tests of a suprapubic or catheter obtained urine.’ Those who have true infection with colony counts less than 100,000 colonies per ml will not be o~~ez-loc~~ed, and those who do not have urinary tract infections but who would have a clean-catcli midstream urine specimen contaminated with greater than 100,000 colonies per ml will be eliminated. References 1.
Boehm, J. J., and Haynes, J. L.: "midstream
catch" urines. Am. J.
Bacteriology of Dis. Child 111:
366, 1966.
T. F., and Meyers, A.: Survey of management of urinary tract infections in
2. Dolan,
office child-
3.
hood. Pediatrics 52: 21, 1973. .: Diagnosis of urinary tract Dove, G. A., et al infections in general practice. Lancet 2: 1281,
4.
Kass, E.
1972.
of the
H.: Bacteriuria and diagnosis of infection urinary tract. Arch. Intern. Med. 100:
709, 1957.
Köhler, L., Fritz, H., and Schersten, B.: Health control of the four-year-old child: A study of bacteriuria. Acta Paediatr. Scand. 61: 289, 1972. 6. Kunin, C. M., Southhall, I., and Paquin, A. J.:
5.
Epidemiology of urinary
tract infections. N.
Engl.
Med. 817, 1960. J. 263: 7.
—:
Detection, Prevention, and Management of Tract Infections. Philadelphia, Lee &
Urinary
Febiger, 8.
1972.
Pryles, C. V., and Lustik, B.: Laboratory diagnosis of urinary tract infections. Pediatr. Clin. North Am. 18: 233, 1971.
9.—: Comparative study of urine obtained from children by percutaneous suprapubic aspirations of the bladder and by catheter. Pediatrics 24: 938, 1959. 10. Stamey, T.: Urinary Tract Infections. Baltimore, Williams and Wilkins, 1972.
701
Downloaded from cpj.sagepub.com at Purdue University on June 14, 2015
