Should blood cultures be ordered for suspected pubic osteomyelitis in afebrile (without fever) patients with no overt infectious signs?

Blood Cultures in Suspected Pubic Osteomyelitis in Afebrile Patients

Blood cultures should be obtained in all patients with suspected pubic osteomyelitis, even in afebrile patients with no overt infectious signs, as recommended by the Infectious Diseases Society of America guidelines. 1

Diagnostic Approach to Pubic Osteomyelitis

Initial Evaluation

• The 2015 IDSA guidelines for vertebral osteomyelitis strongly recommend obtaining bacterial (aerobic and anaerobic) blood cultures (2 sets) and baseline ESR and CRP in all patients with suspected osteomyelitis, regardless of fever status 1
• While these guidelines specifically address vertebral osteomyelitis, the principles apply to pubic osteomyelitis due to similar pathophysiology of hematogenous seeding

Rationale for Blood Cultures in Afebrile Patients

1. Absence of fever does not rule out infection:

   • Fever is present in only up to 45% of patients with bacterial osteomyelitis 1
   • Afebrile presentation is common in osteomyelitis, particularly in subacute or chronic cases

2. Diagnostic yield:

   • Blood cultures can identify the causative organism without requiring invasive bone biopsy
   • Positive blood cultures may obviate the need for image-guided aspiration biopsy 1

3. Clinical differentiation challenges:

   • Pubic osteomyelitis often mimics non-infectious conditions like osteitis pubis 2, 3
   • Cases initially diagnosed as osteitis pubis have later been confirmed as osteomyelitis 2

Special Considerations for Pubic Osteomyelitis

Diagnostic Challenges

• Pubic osteomyelitis is rare, accounting for only 2% of hematogenous osteomyelitis 4
• Presentation can be subtle with groin, hip, or perineal pain and pubic symphysis tenderness 5
• Radiographic changes may be delayed, requiring a high index of suspicion 5

Diagnostic Algorithm

1. Obtain blood cultures (2 sets) and inflammatory markers (ESR, CRP) in all suspected cases
2. Proceed with MRI as the preferred imaging modality
3. If blood cultures are negative and diagnosis remains uncertain:
   • Consider CT-guided aspiration/biopsy of the pubic symphysis 2, 3
   • Open biopsy may be necessary if less invasive methods are non-diagnostic 2

Caveats and Pitfalls

• Prior antibiotic use: Administration of antibiotics before obtaining cultures reduces recovery rates by 35-40% 6
• False negatives: Negative blood cultures do not rule out osteomyelitis 6
• Polymicrobial infections: Blood cultures may not identify all organisms in mixed infections 1
• Diagnostic confusion: Distinguishing between infectious osteomyelitis and non-infectious osteitis pubis can be challenging and may require bone biopsy for definitive diagnosis 3

Summary

Blood cultures are an essential component of the diagnostic workup for suspected pubic osteomyelitis, even in afebrile patients without obvious infectious signs. They should be obtained before initiating antibiotics to maximize diagnostic yield and potentially avoid more invasive procedures.