When evaluating patients for infection, it is essential to first consider potential sources of infection. Many clinical sites (sputum, urine, wounds, or ulcers) are not sterile. Isolating an organism from a nonsterile site does not equate to infection and may lead to inappropriate antimicrobial use. For example, a positive sputum culture reflects the organism’s colonization of the respiratory tract and not pneumonia, unless it is associated with other clinical and radiographic findings. Similarly, obtaining a blood culture from a CVC poses the risk of isolating a contaminant or colonizing a catheter hub (unless paired blood cultures are done with an evaluation of time to positive blood cultures). Similarly, many patients may have asymptomatic bacteriuria (especially the elderly), and a positive urine culture is not necessarily indicative of a urinary tract infection especially in patients with indwelling UCs.
Obtaining any culture needs to be based on a suspicion of infection of the site cultured. Cultures from nonsterile sites may trigger inappropriate antimicrobial use and risk patient harm.
Why Send Urine Cultures Only When Necessary?
Obtaining urine cultures in patients with indwelling UCs can lead to inadvertent increased antimicrobial use, thus resulting in more antimicrobial resistance, Clostridium difficile infection, and adverse drug effects. Thus, the appropriate use of urine cultures enhances patient safety. In addition, the inappropriate use of urine cultures may lead to an increase in observed CAUTI events based on surveillance definitions, although not clinically relevant. Since the presence of bacteriuria is one of the elements necessary for the National Healthcare Safety Network (NHSN) definition of CAUTI, obtaining unnecessary urine cultures in the presence of fever attributed to another source may falsely increase the NHSN CAUTI rate, thereby overestimating CAUTI events. In addition, CAUTI is publicly reported, and patients will be able to compare hospitals based on their CAUTI rates. Patients may perceive hospitals with higher CAUTI rates as providing less than optimal care. The practice of obtaining urine cultures without appropriate indications may falsely increase the publicly reported CAUTI rates, even if the patients do not have clinical signs and symptoms.
Indications for Urine Cultures
Many clinicians order urine cultures in catheterized patients who are asymptomatic. There are very few indications for urine cultures in asymptomatic catheterized patients. The Infectious Diseases Society of America (IDSA) indications for screening patients for bacteriuria are (1) prior to transurethral resection of the prostate, (2) before urologic procedures in which mucosal bleeding is anticipated, and (3) in pregnant women (once in early pregnancy). Obtaining urine cultures in other groups of asymptomatic patients is not recommended. For example, urine cultures should not be done on asymptomatic nonpregnant women, patients with diabetes, elderly patients, patients with a spinal cord injury, or patients with an indwelling UC. Certain groups of patients have a high incidence of asymptomatic bacteriuria (but do not have an active infection). For example, up to 15 percent of elderly women in the community have asymptomatic bacteriuria; this increases to 25–50 percent in elderly female residents of long-term care facilities. In addition, bacteriuria is universal in patients with an indwelling UC for more than 1 month. The high prevalence of bacteriuria in certain populations may be associated with a misdiagnosis of CAUTI and inappropriate antimicrobial use if urine cultures are obtained without a pertinent reason.
What Triggers Urine Cultures?
Obtaining urine cultures depends on the current practice at the hospital. Practices such as “screening culture on admission” and “standing orders” or “reflex orders” for urine cultures based on urinalysis results may lead to inappropriate urine culture and unnecessary antimicrobial use. These practices may increase utilization of additional resources (testing, antibiotics, consultations), and adversely affect patients by exposing them to inappropriate testing and treatments. Physicians tend to treat for CAUTI inappropriately in older patients and in those with gram-negative organisms in the urine or higher numbers of white cells. The IDSA guidelines discourage the use of pyuria, urine odor, color, or turbidity to trigger urine cultures. Multiple studies have shown no relationship between pyuria and symptomatic CAUTI, making the presence of white cells in urine not useful in evaluating for catheter-associated bacteriuria or CAUTI. On the other hand, a urinalysis devoid of white cells may be a good predictor of the absence of bacteriuria in catheterized patients.
How To Reduce Unnecessary Urine Cultures?
We suggest doing the following:
- Discourage automatic or reflex culturing. Ordering cultures should be based on the clinical evaluation of the patients for potential sources of sepsis.
- Provide education about when it is appropriate to obtain urine cultures in patients with an indwelling UC to physicians, midlevel providers, and nurses (see suggestions in table below).
- Have periodic audits on urine culture use in the ICUs to look for trends, especially if CAUTI rates are not dropping with interventions focused on improving insertion and maintenance.
- Promote appropriate UC use to reduce risk of bacteriuria and symptomatic CAUTI (no catheter, no CAUTI).
- Use UCs only based on appropriate indications (with prompt removal when they are no longer needed). The absence of the catheter reduces the risk of bacteriuria and the likelihood of obtaining a urine culture without an appropriate reason.
What To Do With Positive Urine Cultures?
The best way to avoid inappropriate antimicrobial use is not to obtain a urine culture unless indicated. Treatment with antimicrobials should be discouraged in cases where a urine culture turns positive in a catheterized patient who has no symptoms or signs of infection. The IDSA guidelines strongly discourage the use of antimicrobials for asymptomatic bacteriuria except for patients undergoing urologic procedures or who are pregnant.
In patients with symptoms, the IDSA guidelines list “signs and symptoms compatible with CAUTI include new onset or worsening of fever, rigors, altered mental status, malaise, or lethargy with no other identified cause; flank pain; costovertebral angle tenderness; acute hematuria; pelvic discomfort; and in those whose catheters have been removed, dysuria, urgent or frequent urination, or suprapubic pain or tenderness.” Local signs are rarely documented, which makes the clinical diagnosis of CAUTI mainly a diagnosis by exclusion of other sources of infection.
Table 1 below summarizes situations when urine cultures should or should not be obtained in the catheterized patient.
Table 1. When To Obtain or Not Obtain a Urine Culture in a Patient With an Indwelling Urinary Catheter
| Discourage Urine Culture Use | Appropriate Urine Culture Use | |
|---|---|---|
| Urine quality: color, smell, sediments, turbidity (these characteristics do not constitute signs of infection) | Based on local findings suggestive of CAUTI (example, pelvic discomfort or flank pain) | |
| Standing orders for urinalysis or urine cultures without an appropriate indication | Prior to urologic surgeries where mucosal bleeding anticipated or transurethral resection of prostate | |
| Automatic or reflex culturing (mindfulness in evaluating source is key) | Early pregnancy (avoid urinary catheters if possible) | |
| Obtaining urine cultures based on pyuria in an asymptomatic patient | ||
| Asymptomatic elderly and diabetics (high prevalence of asymptomatic bacteriuria) | ||
| Repeat urine culture to document clearing of bacteriuria (no clinical benefit to patients) |
