Urine source
UTI antibiotic resistance is measured in your own urine isolates, not a national average
Urine is the highest volume specimen most laboratories process, which makes it the one source where a facility almost always has enough isolates to cut by unit, by quarter and by organism.
Short answer
UTI antibiotic resistance is local. A national figure for Escherichia coli against ciprofloxacin cannot tell you what to start in your emergency department, because your own outpatient and inpatient urine populations differ from each other, let alone from the country. The answer is a urine-source antibiogram built from your own isolates.
Why the urine cut is the one worth making first
Empiric treatment of urinary tract infection is where a local antibiogram changes prescribing fastest, because the decision is made constantly, usually without culture results in hand, and usually by clinicians who are not infectious disease specialists. Nitrofurantoin, trimethoprim-sulfamethoxazole and a fluoroquinolone are the recurring options, and the choice between them is entirely a question of local susceptibility.
It is also the cut with the most data behind it. Urine is typically the largest single specimen source in the laboratory, so a urine-only antibiogram will usually clear the 30-isolate reporting threshold in every cell that matters, and often clears it quarter by quarter as well.
Outpatient urine and inpatient urine are two different reports
A facility-wide Escherichia coli line blends a community population with a catheterised inpatient population that has seen far more antibiotics. The blend is not wrong, it is simply not the number either prescriber needs. Splitting by unit usually widens the fluoroquinolone gap noticeably, and it is the gap, not the average, that should drive the empiric guideline.
The builder on the homepage does exactly this on a synthetic dataset: set the source to urine, then move the unit filter between outpatient and intensive care and watch the ciprofloxacin column re-tint.
- Outpatient urine, for the community guideline and the urgent care order set
- Inpatient and long term care urine, where prior exposure is heavier
- Catheter-associated isolates, if your export flags them
- Escherichia coli alone, since it dominates the source and drives the guideline
Nitrofurantoin is the reason the organism split matters
Nitrofurantoin concentrates in urine and is a first line agent for uncomplicated cystitis caused by Escherichia coli. It is not a reasonable option for Proteus mirabilis, and its usefulness against Klebsiella pneumoniae is limited. An antibiogram that reports one nitrofurantoin figure across all urinary isolates hides all of that.
Reporting organism by organism, with the isolate count under each number, is what makes the difference visible. That is why every tile in the builder carries its own n.
Related reading: empiric therapy driven by local data, the annual hospital antibiogram. The four steps from susceptibility testing data to an antibiogram cover the method end to end.
Questions
On this page's topic
How many urine isolates do I need for a useful cut?
Aim for at least 30 isolates in each organism and drug cell you intend to report, which is the CLSI M39 guidance and the default threshold in the builder. Most facilities clear it easily for Escherichia coli in urine, and clear it for the next two or three organisms across a full year.
Should I exclude repeat isolates from the same patient?
Yes. Recurrent urinary tract infection means repeat cultures from the same patients, and those patients are more likely to carry resistant organisms. The first isolate per patient rule exists precisely for this source.
Can I separate catheter-associated isolates?
If your export carries a field that identifies them, it becomes another filter. If it does not, the unit cut is usually the practical proxy.
More on antimicrobial resistance reporting
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- CLSI breakpoints A breakpoint revision can move a susceptibility rate by several points without one organism...
- WHONET WHONET is good software, it is free, and it is the global default for a reason. This page is...
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