Should a provider treat an 18-year-old patient with a urine culture positive for Corynebacterium species?

Treatment of Corynebacterium Species in Urine Culture

No, a provider should not treat an 18-year-old patient with 200 colonies of Corynebacterium species in a urine culture, as Corynebacterium species are not considered clinically relevant urine isolates in otherwise healthy young patients and typically represent contamination or colonization rather than true infection. 1

Guideline-Based Rationale

The American Academy of Pediatrics explicitly states that organisms such as Corynebacterium species, coagulase-negative staphylococci, and Lactobacillus species are not considered clinically relevant urine isolates for otherwise healthy children and young adults aged 2 to 24 months (and by extension, healthy young adults). 1 This principle applies to an 18-year-old patient without significant comorbidities.

Key Diagnostic Considerations

Colony count threshold: The reported 200 colonies falls far below the threshold for significant bacteriuria. For clean-catch or catheterized specimens, at least 50,000 CFU/mL of a single urinary pathogen is required to define significant bacteriuria. 1 The extremely low colony count of 200 strongly suggests:

• Contamination from periurethral or skin flora 1
• Colonization without clinical infection 1
• Laboratory artifact 1

Clinical context matters: Treatment decisions should integrate:

• Presence or absence of urinary symptoms (dysuria, frequency, urgency, suprapubic pain) 1
• Fever or systemic signs of infection 1
• Urinalysis findings (pyuria, positive leukocyte esterase, nitrites) 1
• Patient's immune status and comorbidities 2

When Corynebacterium Species ARE Clinically Significant

While treatment is not indicated in this case, providers should recognize rare scenarios where Corynebacterium species cause true urinary tract infections:

High-Risk Patient Populations

Immunocompromised patients: Corynebacterium species can cause serious infections in patients on high-dose steroids, transplant recipients, or those with significant immunosuppression. 3, 2

Patients with urologic abnormalities: Those with:

• Indwelling urinary catheters (especially if in place ≥2 weeks) 4, 2
• Recent urologic procedures or instrumentation 2
• Structural urinary tract abnormalities 2
• History of recurrent UTIs 2

Elderly patients: Age >65 years with underlying urologic disease increases risk of true Corynebacterium UTI. 2

Specific Pathogenic Species

Corynebacterium urealyticum (formerly group D2): This species causes encrusted cystitis, a severe chronic infection leading to bladder necrosis, renal failure, and potentially death. It requires prolonged incubation for detection and presents with alkaline urine. 3, 2

Other pathogenic species: C. coyleae has been documented causing complicated UTIs requiring nephrectomy, and C. aurimucosum has been isolated from urine in post-surgical patients. 5, 6

Clinical Pitfalls to Avoid

Do not treat asymptomatic bacteriuria: The Infectious Diseases Society of America strongly recommends against routine screening for and treatment of asymptomatic bacteriuria, even in catheterized patients (with specific exceptions like pregnancy). 1, 4 Treatment promotes antimicrobial resistance without clinical benefit. 1, 4

Do not reflexively treat low colony counts: Colony counts below established thresholds (50,000 CFU/mL for most collection methods) typically represent contamination, not infection. 1

Recognize when cultures may be misleading: Corynebacterium species are fastidious organisms requiring prolonged incubation; cultures may initially appear sterile. 2 However, this applies when clinical suspicion is high, not in asymptomatic patients with minimal growth.

Recommended Approach for This Patient

If the patient is asymptomatic:

• No treatment is indicated 1
• No repeat culture is necessary 1
• Reassure the patient that this represents normal skin flora contamination 1

If the patient has urinary symptoms:

• Obtain a properly collected urine specimen (catheterized specimen preferred to minimize contamination) 1
• Perform urinalysis looking for pyuria (≥5 WBCs/hpf), positive leukocyte esterase, or positive nitrites 1
• If urinalysis is negative and symptoms are mild, consider alternative diagnoses 1
• If urinalysis is positive with significant pyuria, repeat culture with proper collection technique 1

If repeat culture grows Corynebacterium species with high colony counts (≥50,000 CFU/mL) in a symptomatic patient:

• Consider this a true infection requiring treatment 2
• Perform antimicrobial susceptibility testing, as Corynebacterium species show unpredictable resistance patterns 7
• Vancomycin shows consistent activity, but doxycycline and fusidic acid are also often effective 7
• Evaluate for underlying urologic abnormalities or immunosuppression 2, 6