Is Streptococcus anginosus clinically significant in urinary tract infection?

Streptococcus anginosus in UTI: Clinical Significance

Streptococcus anginosus is generally NOT a clinically significant pathogen in urinary tract infections and should not be routinely treated when isolated from urine cultures.

Key Evidence and Rationale

The major international UTI guidelines 1 from the European Association of Urology (2024) consistently identify the typical uropathogens as:

• E. coli
• Proteus spp.
• Klebsiella spp.
• Pseudomonas spp.
• Serratia spp.
• Enterococcus spp.

Notably, S. anginosus is conspicuously absent from all guideline-recommended pathogen lists for both uncomplicated and complicated UTIs.

Understanding S. anginosus in the Urogenital Tract

Recent genomic research reveals important context:

Colonization vs. Infection

• S. anginosus is a normal colonizer of the urogenital tract, not a true uropathogen 2, 3
• A distinct genomic group (group "Urinae") shows tropism for urogenital sites but represents colonization rather than infection 3
• The same strain can be isolated across multiple urogenital sites (urine, vagina, urethra, perineum) in the same individual, confirming its role as commensal flora 2

Historical Evidence

• A 1983 study specifically investigated S. milleri (which includes S. anginosus) as a potential urinary pathogen and concluded: "Although these strains frequently are isolated from urine, they appear to play no pathogenic role in urinary tract infections" 4

Site-Specific Associations

• When S. anginosus does cause true infection, it is associated with:
  • Genitourinary infections in children (particularly balanoposthitis) 5
  • Abscesses in various body sites 6
  • NOT typical cystitis or pyelonephritis

Clinical Decision Algorithm

When S. anginosus is isolated from urine:

1. Assess for UTI symptoms:

   • If asymptomatic → Do NOT treat (consistent with asymptomatic bacteriuria guidelines) 1
   • If symptomatic → Consider alternative explanations

2. If symptomatic, evaluate for:

   • Polymicrobial infection (>70% of S. anginosus infections are polymicrobial) 5
   • Presence of typical uropathogens (E. coli, Klebsiella, etc.)
   • Structural abnormalities or abscess formation
   • Alternative diagnoses (balanoposthitis in males, vaginitis in females)

3. Treatment decision:

   • Do NOT treat S. anginosus as a sole urinary pathogen
   • Treat only if part of documented polymicrobial infection with recognized uropathogens
   • Consider structural evaluation if recurrent isolation

Important Caveats

• S. anginosus can harbor plasmids with antibiotic resistance genes 7, but this does not make it a pathogen requiring treatment
• Its nuclease activity may facilitate survival of co-pathogens in polymicrobial infections 8, so carefully evaluate for other organisms
• In catheterized patients, S. anginosus likely represents catheter-associated colonization, not infection, unless accompanied by systemic symptoms and recognized uropathogens

Bottom Line

Treat the patient, not the culture result. S. anginosus in urine represents urogenital colonization in the vast majority of cases. Focus diagnostic and therapeutic efforts on identifying true uropathogens listed in current guidelines 1 rather than treating this commensal organism.