What is the best course of treatment for an adult patient, possibly immunocompromised or elderly, with back pain and a lumbar x-ray indicating an Aerococcus urinae infection, susceptible to penicillin, amoxicillin, piperacillin, cefepime, rifampin, and nitrofurantoin?

Critical Clarification: This is NOT a Urinary Tract Infection

The clinical scenario describes back pain with a lumbar x-ray result that has been incorrectly reported—a lumbar x-ray cannot detect Aerococcus urinae, which is a bacterium found only in urine cultures. This appears to be a documentation error where either: (1) urine culture results were mistakenly attributed to an x-ray report, or (2) the patient has concurrent back pain and an incidental positive urine culture.

Immediate Diagnostic Priorities

You must first determine if this patient has vertebral osteomyelitis (spondylodiscitis) versus simple back pain with asymptomatic bacteriuria. This distinction is life-altering for morbidity, mortality, and quality of life.

Suspect Vertebral Osteomyelitis If:

• New or worsening back pain PLUS fever 1
• New or worsening back pain PLUS elevated ESR or CRP 1
• New or worsening back pain PLUS bloodstream infection 1
• New neurologic symptoms (with or without back pain) 1
• Recent history of bacteremia in the past year 1

Obtain Immediately:

• Two sets of blood cultures (aerobic and anaerobic) before any antibiotics 1
• Baseline ESR and CRP 1
• Spine MRI with contrast—this is the gold standard imaging study 1
• Pertinent neurologic examination assessing motor and sensory function 1

Treatment Algorithm Based on Clinical Scenario

Scenario 1: Vertebral Osteomyelitis (Spondylodiscitis) Confirmed or Highly Suspected

Treat aggressively with IV antibiotics targeting Aerococcus urinae for 6-8 weeks minimum, as this is a life-threatening infection with risk of permanent spinal cord injury and septicemia. 1, 2, 3

Antibiotic Selection for Invasive Aerococcus urinae Infection:

• First-line: IV penicillin G or IV ampicillin (Aerococcus urinae shows universal susceptibility to penicillins) 4, 5, 2, 3
• Alternative: IV amoxicillin (if oral transition needed after clinical improvement) 4, 5, 3
• Duration: Minimum 4-6 weeks IV therapy, followed by prolonged oral therapy (total 3-6 months) 2, 3

The only reported case of Aerococcus urinae spondylodiscitis was successfully treated with 4 weeks of IV amoxicillin plus clindamycin, followed by 5 months of oral amoxicillin 3. A more recent case of thoracic spondylodiscitis with bacteremia received prolonged combination therapy 2.

Critical Management Points:

• Consult infectious disease and spine surgery immediately 1
• Obtain tissue/bone biopsy if blood cultures negative to confirm pathogen 1
• Monitor inflammatory markers (ESR/CRP) weekly to assess treatment response 1
• Repeat MRI at 4-6 weeks to assess progression 1

Scenario 2: Simple Back Pain with Asymptomatic Bacteriuria

Do not treat the bacteriuria—treatment is contraindicated and harmful. 1, 6, 7

Rationale for No Treatment:

• Asymptomatic bacteriuria in elderly or immunocompromised adults should never be treated 1, 6
• Treatment increases antimicrobial resistance without clinical benefit 1, 6, 7
• Randomized trials show similar mortality rates at 9 years whether treated or not, but significantly more adverse drug events and resistant organisms in treated patients 6
• The presence of bacteria in urine without urinary symptoms (dysuria, frequency, urgency, fever, gross hematuria) represents colonization, not infection 6, 7

When Bacteriuria DOES Require Treatment:

• Only if patient has specific urinary symptoms: fever, dysuria, suprapubic pain, rigors, or hemodynamic instability 6, 7
• Pregnant women (not applicable here) 6
• Before urologic procedures with mucosal bleeding 6

Scenario 3: Symptomatic Urinary Tract Infection (Without Vertebral Involvement)

If the patient has urinary symptoms (dysuria, frequency, urgency, fever from urinary source), treat with:

First-line: Oral amoxicillin 500 mg every 8 hours for 7-14 days 4, 5, 8

• Aerococcus urinae shows 100% susceptibility to amoxicillin and penicillin 4, 5
• Alternative: Nitrofurantoin 100 mg every 6 hours (71-76% clinical success for A. urinae cystitis) 5, 8
• Avoid sulfonamides—100% resistance 4, 5
• Fluoroquinolones have variable susceptibility (78% susceptible to norfloxacin) 5

For complicated UTI or pyelonephritis: Consider IV piperacillin or cefepime initially, then transition to oral amoxicillin 4

Common Pitfalls to Avoid

• Treating asymptomatic bacteriuria "just to be safe"—this causes harm through resistance and adverse effects 1, 6, 7
• Missing vertebral osteomyelitis by attributing back pain to musculoskeletal causes—delays in diagnosis average 2-4 months and lead to permanent neurologic injury 1
• Relying on x-rays for infection diagnosis—x-rays cannot detect bacteria; MRI is required for spinal infection 1
• Using sulfonamides for Aerococcus urinae—universal resistance 4, 5
• Inadequate treatment duration for invasive infection—spondylodiscitis requires months of therapy 2, 3