Each year, there are more than 1 million ED visits for urinary tract infection (UTI) in the United States.1 Antibiotic treatment for UTIs is avoidable in a significant proportion of patients. Emergency physicians tend to overdiagnose and overtreat because asymptomatic bacteriuria is very common in all age groups, urine cultures are frequently ordered without an appropriate indication, and urinalysis results are often misinterpreted. In this column, my aim is for you to reflect on your practice when it comes to UTI diagnosis and treatment.
Explore This IssueACEP Now: Vol 37 – No 01 – January 2018
Which Historical Features Are Useful?
No single clinical symptom, sign, or lab test is accurate enough to rule in or out a UTI.2 Only about half of patients who present with dysuria and frequency will have a UTI. However, for those patients who present with dysuria and frequency and do not have any symptoms suggesting vaginitis or cervicitis (vaginal irritation, bleeding, and discharge), the likelihood of a UTI increases to more than 90 percent, with a positive likelihood ratio (+LR) of 24.6.2 Other helpful historical features include a self-diagnosed UTI, which has a +LR of 4 (as good as a positive dipstick), and cloudy urine appearance in a noncatheterized patient, which has a specificity of 96 percent for UTI.2
Which Patients Require a Workup?
Urine tests are not required for the majority of patients with suspected lower UTI, as it is a clinical diagnosis and the urine tests can be misleading, resulting in over- and undertreatment. Urine tests are usually not necessary for very-low-risk patients or for patients with a very convincing clinical presentation, as your posttest probability will not be changed significantly.
Indications for urine tests for suspected lower UTI include those patients with an intermediate pretest probability for UTI, immunocompromised patients, a history of multiple courses of antimicrobial therapy, a history of antibiotic resistance, or a history of multiple drug allergies. Remember that even a urine culture has a 5 percent false-positive rate due, in large part, to asymptomatic bacteriuria and a 25 percent false-negative rate due to antibiotic use and sample overdilution.2
Think About Differential Diagnosis of Pyuria
Not all pyuria is caused by UTI. Pyuria can result from a wide array of conditions. Dehydration, acute renal failure, sexually transmitted infections, appendicitis, diverticulitis, and the presence of a bladder catheter can all cause white blood cell counts of more than 5 cells/mL on microscopy. While pyuria on its own has a sensitivity as high as 94 percent, its specificity is poor unless combined with positive nitrite. Pyuria and positive nitrite in the setting of a clinical history for UTI has a specificity of 100 percent. However, if microscopy in isolation is used, the result is overtreating 44 percent and undertreating 11 percent of UTIs.4 The urine dipstick is even worse. If the dipstick is used in isolation, UTIs are overtreated 47 percent and undertreated 13 percent.
Interpreting Epithelial Cells and Bacteria on Urine Microscopy
The classic teaching is that more than five epithelial cells per high-powered field represents an uncontaminated sample.4 However, while a “contaminated” sample may negatively affect the ability to obtain a reliable culture, it does not affect the accuracy of the dipstick or microscopy to the same degree. While bacteria seen on microscopy is predictive of a positive culture, it is not necessarily diagnostic of a UTI, as the positive culture could represent a contaminant or asymptomatic bacteriuria. Just as bladder catheters can cause pyuria, they can cause bacteriuria without UTI as well.5
Which Patients Require Antibiotics for Asymptomatic Bacteriuria?
According to the Infectious Diseases Society of America, asymptomatic bacteriuria is not linked to long-term adverse outcomes, and treatment does not decrease the rate of symptomatic UTI.6 Asymptomatic bacteriuria is very common in all age groups and is often misdiagnosed as a UTI. Antibiotics for asymptomatic bacteriuria should only be considered in patients undergoing an invasive urologic procedure and in pregnant patients.
There is no evidence that routine prophylactic antibiotic treatment in patients with bladder catheters in the emergency department reduces the incidence of UTI.7 It is important to remember that nearly all patients with an indwelling catheter are colonized with two to five organisms within two weeks of placement, and the number of white blood cells found is not predictive of UTI.5 Candida is commonly found in the urine of catheterized patients. Do not treat with antifungals unless the patient is neutropenic or has risk factors for systemic candidiasis. Conservative management, which includes replacement or removal of the catheter and observation, will suffice for most.
Approach to Altered Older Patient with Abnormal Urine Microscopy
Clinically stable older patients with acute altered mental status (AMS) without other signs or symptoms of UTI who are found to have bacteriuria and/or pyuria in the emergency department should be observed for resolution of confusion for 24–48 hours without antibiotics.8,9 Attributing AMS in an older patient to a UTI in the absence of other signs and symptoms of UTI can result in premature closure and missing life-threatening alternative causes of AMS. The diagnosis of UTI in the altered older patient should be thought of as a diagnosis of exclusion.
Choosing Antibiotics for UTI
Choose a narrow-spectrum antibiotic with the safest side effect profile, taking local resistance patterns into consideration whenever possible. The antibiotic choice should reflect its ability to eradicate E. coli, the most common bacteria found in 70 percent to 95 percent of lower UTIs, rather than more infrequently colonized bacteria such as Pseudomonas, which are found predominantly in patients with upper UTI, immunocompromised patients, or those with genitourinary anatomical abnormalities. Fluoroquinolones, such as ciprofloxacin, that Pseudomonas are susceptible to should be avoided for the treatment of lower UTI because resistance to ciprofloxacin is increasing globally.10 Note also that a three- to six-day duration of therapy is sufficient for the majority of patients with lower UTI.11 Fosfomycin has the advantage of requiring only a single oral dose, but it should be reserved for outpatient management of multidrug-resistant recurrent UTIs.12
Are Urinary Anesthetics Such as Phenazopyridine Recommended?
While phenazopyridine may provide symptomatic relief for UTI, it has the potential to cause serious side effects such as hemolysis in patients with G6PD deficiency and methemoglobinemia.13
Take-Home Points for UTIs
- UTI is a clinical diagnosis, not a laboratory one. Dysuria and urinary frequency in the absence of symptoms of vaginitis/cervicitis is diagnostic.
- No single clinical symptom, sign, or lab test is accurate enough to rule in or out UTI.
- Most patients with a clinical picture consistent with lower UTI do not require urine tests.
- The indications for urine tests for suspected lower UTI include those with moderate pretest probability, immunocompromised patients, history of multiple courses of antimicrobial therapy, history of antibiotic resistance, and history of multiple drug allergies.
- While the finding of bacteria on microscopy is predictive of a positive culture, it is not necessarily diagnostic of UTI, as the positive culture could represent contaminant or asymptomatic bacteriuria.
- A common pitfall is treating nonpregnant patients with asymptomatic bacteriuria with antibiotics. Asymptomatic bacteriuria is very common in all age groups and is often misdiagnosed as UTI.
- Do not routinely treat catheterized patients with pyuria or Candida in their urine.
- A common pitfall is to assume that the cause of AMS in an older patient is a UTI upon finding pyuria or bacteriuria on urinalysis, leading to premature closure and missing a more serious diagnosis.
- Three- to six-day duration of therapy is sufficient for the vast majority of lower UTIs.
- Niska R, Bhuiya F, Xu J. National hospital ambulatory medical care survey: 2007 emergency department summary. Natl Health Stat Rep. 2010;(26):1-31.
- Aubin C. Evidence-based emergency medicine/rational clinical examination abstract. Does this woman have an acute uncomplicated urinary tract infection? Ann Emerg Med. 2007;49(1):106-108.
- Lammers RL, Gibson S, et al. Comparison of test characteristics of urine dipstick and urinalysis at various test cutoff points. Ann Emerg Med. 2001;38(5):505–512.
- Lane DR, Takhar SS. Diagnosis and management of urinary tract infection and pyelonephritis. Emerg Med Clin North Am. 2011;29(3):539-552.
- Stark RP, Maki DG. Bacteriuria in the catheterized patient. What quantitative level of bacteriuria is relevant? N Engl J Med. 1984;311(9):560-564.
- Nicolle LE, Bradley S, Colgan R, et al. Infectious Diseases Society of America guidelines for the diagnosis and treatment of asymptomatic bacteriuria in adults. Clin Infect Dis. 2005;40(5):643-654.
- Garnham F, Smith C, Williams S. Best evidence topic report. Prophylactic antibiotics in urinary catheterisation to prevent infection. Emerg Med J. 2006;23(8):649.
- Beveridge LA, Davey PG, Phillips G, et al. Optimal management of urinary tract infections in older people. Clin Interv Aging. 2011;6:173-180.
- Nicolle LE. Asymptomatic bacteriuria in institutionalized elderly people: evidence and practice. CMAJ. 2000;163(3):285-286.
- Bouchillon S, Hoban DJ, Badal R, et al. Fluoroquinolone resistance among gram-negative urinary tract pathogens: global smart program results, 2009-2010. Open Microbiol J. 2012;6:74-78
- Lutters M, Vogt-Ferrier NB. Antibiotic duration for treating uncomplicated, symptomatic lower urinary tract infections in elderly women. Cochrane Database Syst Rev. 2008;(3):CD001535.
- Sultan A, Rizvi M, Khan F, et al. Increasing antimicrobial resistance among uropathogens: is fosfomycin the answer? Urol Ann. 2015;7(1):26-30.
- Dart RC, ed. Medical Toxicology. 3rd ed. Philadelphia: Lippincott Williams & Wilkins; 2004.