Letters, 9/13

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University of Alberta
Edmonton, Alberta
Canada

Lance Peterson, MD, epidemiologist and director of microbiology and infectious diseases research, and Tom Thomson, PhD, director of the microbiology laboratory and division head of clinical pathology, NorthShore University HealthSystem, Evanston, Ill., reply:
Your initial comment regarding inappropriate prescribing of antibiotics for patients whose urine cultures are reported with organism identification and antibiotic susceptibilities but who do not have urinary tract infection is a result of many physicians who send urine for culture inappropriately. A major reason for this is that many physicians consider both the urinalysis and the urine culture a diagnostic test and have linked a wide variety of clinical symptoms to the potential presence of a UTI, then conclude an infection is present whenever the laboratory reports the culture as positive for any growth. Such vague symptoms include fatigue, increased confusion in a mentally impaired patient, and dehydration in a long-term care facility resident. We feel that it is the responsibility of the clinical laboratory physician or medical microbiologist to determine how test reporting affects patient care in their practice and modify either the testing or the reporting so that laboratory results are used most appropriately. In our initial review of how the urine culture report was being used at our inpatient facilities we determined that by raising the reporting threshold to ≥10⁵cfu/mL we improved the likelihood that this report indicated the presence of a clinically significant health-care–associated UTI by 74-fold.¹ In that study, patients with urine cultures growing ≤10⁵cfu/mL had less than a six percent chance of having a clinically significant UTI, strongly suggesting that reporting these results as potentially positive was not appropriate for our organization.¹

We also agree that lower microbial counts can occur in patients with clinically significant infection. However, this pertains to patients with signs and symptoms compatible with UTI and no other source of infection; we do not believe that nonspecific deterioration with no evidence of any infection is a relevant sign or symptom. Since a very large number of elderly persons and those residing in long-term care will have some bacteriuria, reporting low colony counts in these patients after hospital admission in the setting of no findings relating to the urinary tract or to some generalized response to infection is not useful and only adds to excessive antimicrobial use. Interestingly, it has also been proposed that the threshold for reporting a positive urine culture be raised for critically ill children,² in a way that is very similar to our new approach. As noted in the Infectious Diseases Society of America guideline, the evidence for any use of a colony count threshold as low as 10³cfu/mL is very weak and based on “opinions of respected authorities … clinical experience, descriptive studies, or reports of expert committees” rather than well-done scientific study.³

Proposing to “ensure cultures are sent appropriately, from patients with symptoms/signs compatible with UTI, and that the specimen is collected so as to minimize contamination” is highly desirable but perhaps unachievable in most practices. In today’s busy practice it is unusual for many providers to document specifically why a urine culture is sent, and the laboratory staff do not have the time to review documentation in the medical record for each urine specimen received; most laboratory staff do not even have access to the patient’s health record. An interesting report assessed the problem of using evidence-based medicine (EBM) for primary care providers. The authors found that practitioners considered “barriers to implementing EBM at the point of care were time constraints, work overload, a busy urban setting, and patients [or relatives] demanding redundant treatment.”⁴ As we move into the future it may well be possible to develop electronic physician prompts that assist the practitioner in deciding when a urine specimen should or should not be sent, but that technical achievement is still a few years away.

To ensure patient safety, we are prospectively reviewing for one year each patient record where bacteria are grown in low numbers from urine specimens and reported as “negative for nosocomial UTI” in order to detect any patient who needs therapy but did not receive it. During the first three months of our new reporting approach, 211 records with low colony counts were reviewed and we found five patients with possible UTI, all of whom were begun on empirical treatment, a rate and outcome consistent with our initial report.¹ Importantly, there were two unintended consequences that followed an inadvertent laboratory result using the previous reporting format when lower counts were sent to the medical record. The first was a patient who was then treated for a UTI while having no clinical findings of infection using a cephalosporin and who developed acute renal injury from the drug; they declined short-term dialysis and chose hospice care where the patient died. The second was a patient, again with no symptoms and a reported low colony count urine culture, who was given a fluoroquinolone and then developed Clostridium difficile infection. It is important for all practitioners to remember that excess antimicrobial agent use not only leads to increasing resistance to these agents but can have severe consequences for individual patients.

At this point in time, our change to a more rational reporting system for hospitalized patients with suspected health-care–associated UTI is working as planned and improving the quality of care for our patients. We feel it is the responsibility of laboratory-based director leadership to continually ensure that the tests being provided and the results reported are appropriate for the practice setting.

1. Kwon JH, Fausone MK, Du H, Robicsek A, Peterson LR. Impact of laboratory reported urine culture colony counts on the diagnosis and treatment of urinary tract infection (UTI) for hospitalized patients. Am J Clin Pathol 2012;137:778–784.
2. Langley JM. Defining urinary tract infection in the critically ill child. Pediatr Crit Care Med 2005;6(3 suppl): S25–29.
3. Hooton TM, Bradley SF, Cardenas DD, Colgan R, et al. Diagnosis, prevention, and treatment of catheter-associated urinary tract infection in adults: 2009 international clinical practice guidelines from the Infectious Diseases Society of America. Clin Infect Dis 2010; 50:625–663.
4. Shuval K, Shachak A, Linn S, Brezis M, et al. The impact of an evidence-based medicine educational intervention on primary care physicians: a qualitative study. J Gen Intern Med 2007;22:327–331.

Setting the bar

I give a lot of infectious disease lectures around the country and read a lot of the trade journals. Many of the “medical” articles in these other publications make me cringe as they are often written by people from companies with an agenda to sell products and can often be against current medical guidelines.

I read your article on “Sizing up ‘mega’ multiplex panels for respiratory viruses” (May 2013) and it is just pleasant to see things well written with the proper medical outcomes. I appreciate what you do and wish other magazines would follow your lead. Time and again, CAP TODAY sets the bar where it should be.

Norman Moore, PhD
Director of Scientific Affairs, Infectious Diseases
Alere

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