Is a urinalysis and culture report showing Enterobacteriaceae (a type of bacteria) with a colony count of less than 10,000 colony-forming units per milliliter (CFU/mL) indicative of a urinary tract infection (UTI)?

From the Guidelines

No, a urinalysis and culture report showing Enterobacteriaceae <10,000 CFU/mL is generally not considered a urinary tract infection (UTI). Typically, the diagnostic threshold for a UTI is ≥100,000 CFU/mL of a single organism in a clean-catch urine specimen, as suggested by the 2019 clinical practice guideline for the management of asymptomatic bacteriuria by the Infectious Diseases Society of America 1. The finding of <10,000 CFU/mL likely represents contamination from the skin or perineal area during collection, or colonization without true infection.

However, clinical context matters - if a patient has symptoms like burning urination, frequency, urgency, or suprapubic pain, lower bacterial counts (10,000-100,000 CFU/mL) might be considered significant, especially in certain populations like pregnant women, elderly patients, or those with indwelling catheters. The American Academy of Pediatrics suggests that an appropriate threshold to consider bacteriuria “significant” in infants and children is the presence of at least 50,000 CFUs per mL of a single urinary pathogen 1, but this may not apply to all populations.

If symptoms are present despite the low bacterial count, the healthcare provider might consider repeating the culture with a more carefully collected specimen or evaluating for other causes of urinary symptoms. The presence of white blood cells (pyuria) in the urinalysis would also be important in determining whether treatment is warranted despite the low bacterial count, as pyuria and/or bacteriuria are required to establish the diagnosis of UTI 1.

Key considerations in the diagnosis of UTI include:

• The method of urine collection, with catheterization or suprapubic aspiration (SPA) being more reliable than clean-catch midstream urine collection
• The presence of pyuria, which can indicate inflammation and infection
• The type of organism isolated, with some organisms being more commonly associated with UTI than others
• The clinical context, including the presence of symptoms and the patient's underlying medical conditions.

In general, the diagnosis of UTI requires a combination of clinical evaluation and laboratory testing, and the presence of Enterobacteriaceae <10,000 CFU/mL is not sufficient to establish a diagnosis of UTI in the absence of other supporting evidence.

From the Research

Urinalysis and Culture Report

A urinalysis and culture report showing Enterobacteriaceae with a colony count of less than 10,000 CFU/mL may be indicative of a urinary tract infection (UTI) in certain cases.

• The study 2 suggests that a reporting threshold of 10,000 CFU/mL is more clinically appropriate than a 100,000 CFU/mL cutpoint for diagnosing UTI.
• However, the presence of symptoms such as dysuria, urgency, and frequency, as well as the patient's medical history and physical examination, should also be taken into account when interpreting the results 3, 4.
• The study 4 found that more than half of the patients whose urine cultures grew Enterococcus spp. in counts lower than 100,000 CFU/mL may have true UTI, especially if they are hospitalized and have symptoms of dysuria, urgency, or frequency.

Colony Count and UTI Diagnosis

• A colony count of less than 10,000 CFU/mL does not necessarily rule out a UTI, as some studies have shown that even low colony counts can be indicative of infection in symptomatic patients 3, 2.
• The study 5 found that clear urine on visual inspection had a negative predictive value of 97.3% for UTI, but it is not a definitive test for ruling out UTI.
• The presence of white cell casts on the examination of the urinary sediment is pathognomonic of upper tract infection and would lead one to pursue an aggressive course of therapy 6.

Clinical Significance

• The clinical significance of bacteriuria with low colony counts of Enterobacteriaceae remains unclear, and the final interpretation should be done by physicians, using additional clinical information 4.
• The study 3 suggests that asymptomatic bacteriuria is common, particularly in older women, and should not be treated with antibiotics, whereas symptomatic women may require treatment even with low colony counts.