Urine culture for women for medical student

2.  9 million doctor visits/year!
 Customary urine test is the dip stick and the mid-stream culture of
voided urine. Up to 77% of cystitis cases are cultured
 Traditionally- >100,000 (10⁵)CFUs was called diagnostic of either
UTI (bladder infection present) or asymptomatic bacteruria.
 More recently as little as 100 CFUs in a voided sample has been
positively correlated with coliform (such as E. coli) bladder infection
 The problem with this cut off: Many labs will call 0 to 10,000 CFUs
(<10⁴) as a negative culture

3. The way the urine test is done, diluting
out the urine 1000 times, there may be
no growth on the agar plates despite a
bladder infection being present

4. What does the results of the urine culture tell you ?
202 paired samples of mid stream collected urine cultures and catheterized bladder cultures in young
woman who had symptoms of uncomplicated cystitis, no features of pyelonephritis
70% of bladder cultures positive
78% of voided mid-stream cultures positive
As few as 10 CFUs of mid-stream cultures of E. coli or Klebsiella pneumoniae– highly correlated with a
true bladder infection ( 93% PPV).
In contrast – 22% of mid- stream cultures grew enterococcus or Group B strep- at even 100,000 (10⁵
CFUs) – there was no correlation with bladder cultures- These bugs were not found in the corresponding
bladder culture, but E.coli was still cultured in the bladder (but not in the mid-stream culture) in 62% of
these cases !
Take Home Message:
I. a young woman with classic cystitis symptoms can have a documented bladder infection, but her
midstream urine culture can still be a false negative test ( too few CFUs to be detected on standard urine
cultures)
II. Positive mid-stream cultures for enterococcus and Group B strep are most likely contaminants
III. In uncomplicated cases- obtaining cultures as a guide to therapy can be counter productive: either not
treating patients with actual infection, or treating patients for the wrong bacteria.

5.  Ask the patient “do you feel like you have a bladder
infection- do you have both a sense of urgency and burnig
when you urinate?”
 Do a dip stick and treat only if leukocytes or nitrite positive?
 Send the urine for culture, wait 2 days, and treat the patient
only if >100,000/ml colonies

6.  Symptoms only: +dysuria, +frequency, no discharge or
irritation:***90% chance of cystitis***
 Dipstick: leukocyte esterase + and/or nitrite + only 75%
sensitive, so symptoms more important even if dip is negative
 Culture:10⁵ (100,000) bacterial CFU- traditional criterion of
UTI- 50% sensitive -will miss up to half of cases of UTI –
counts of 100 to 10,000 colonies – all at levels that may be
called as “no growth” by micro lab. Least sensitive diagnostic
test

7.  **Rarely progresses to severe disease even if untreated:
goal is to ameliorate symptoms
 In selecting therapy, efficacy as well as “ecologic collateral
damage” (selecting for antibiotic resistant bacteria, C. difficile
colitis) should be considered equally- fluoroquinolones
should be avoided, except in pyelonephritis
 Nitrofurantoin, Septra, fosfomycin are therefore first line
agents
 New Study- still >50% of Rxs are for Cipro, most of the time
for > than 3 days. Septra #2, nitro #3 , fosfomycin-no Rx

9.  Definition: presence of bacteria >100,000
cfu/ml in urine of an individual without signs
or symptoms of UTI.
 This definition is independent of the presence
or absence of pyuria, odor, cloudy urine

10.  Very Common:
i. Young healthy women : 3 to 5%
i. Pregnant women: 2 to 9.5%
ii. Women aged 65-80 years: 18 to 43%
iii. Women > 80 years: up to 43%
iv. Men 65-80 years: 2 to 15%
 Causes:
Obstructive uropathy, neuromuscular
disease, perineal soiling in dementia, etc

11.  Traditional teaching:
the presence of bacteriuria defines a population at
risk, therefore:
Eliminating the “asymptomatic UTI” (oxymoron)
minimizes the risk for a clinically symptomatic
disease
Modern Teaching:
 NO benefit to treatment (except in pregnancy and
before urologic procedure). Term changed to
“asymptomatic bacteriuria”

12.  3 to 5% of young women have ABU
 What role does this have in recurrent UTI’s? Many women get
follow-up urine studies and re-treatment after initial therapy
for UTI.
 Study in Clinical Inf. Disease -9/15/2012:
673 healthy non-pregnant woman followed after first UTI for one year.- all
were treated again at any time if had symptomatic UTIs. urine cultures were
also obtained at 3, 6 and 12 months-if positive but if patient asymptomatic
only half were treated, other half were not

13.  Results after one year of observation:
Those treated for ABU- 46.8% had a symptomatic UTI later
during the year
Those not treated for ABU- only 13.1% had another UTI!
Conclusion: The paradoxical result was increased incidence of
symptomatic UTIs in patients given antimicrobials for
asymptomatic bacteruria!

14.  Bacterial interference- the inability of pathogenic
bacteria to set up a bladder infection due to
blockage by commensal bacteria colonizing the
bladder- was disrupted by the treatment of ABU.
Conclusion :The human microbiome is a potent
defense mechanism against superinfecting
pathogenic bacteria. Applies to the bladder, as well
as the GI tract and other sites.

15.  Antibiotic treatment of ASB does not reduce frequency of
symptomatic UTI
 Treatment of ASB in diabetes does not reduce adverse
outcomes, improve glucose control, or reduce symptomatic
UTIs
 It does lead to untreatable drug resistant bacteria, c.diff,etc
 Only exceptions are pregnancy where asymptomatic
bacteriuria is associated with pyelonephritis, growth
retardation, neonatal death… and patients undergoing
urologic procedures (such as prostate bx)

16.  Many older patients get screening u/a’s and reflex cultures even
when they don’t have urgency and burning symptoms. They are
then treated for a “UTI”. This is a too common mistake…
 “older patients should not be tested or treated for UTI unless
they have symptoms”
 If you are treated for a true UTI: no follow-up test of cure should
be performed
 Antibiotics:
have side-effects
can cause future problems like yeast infection and colitis
lead to drug resistant bacteria
are a waste of money

17.  Think twice before ordering a urine culture- go by symptoms
and signs. Only culture in possible pyelonephritis, unclear
diagnosis, complicated cases or treatment failure
 Consider Macrodantin or Septra as first line therapy,
quinolones if they are ill
 Mid-stream culture results with enterococcus and GBS can be
deceiving – rarely cause of UTI. Most likely still E. coli
 If the patient is asymptomatic –if it ain’t broke, don’t fix it!