What are the infectious etiologies of polyarthritis and the recommended first‑line antimicrobial therapy for each pathogen?

Infectious Causes of Polyarthritis and First-Line Antimicrobial Therapy

Bacterial pathogens are the most common infectious causes of polyarthritis, with Staphylococcus aureus being the predominant organism in adults, followed by Neisseria gonorrhoeae in sexually active individuals, and streptococci; viral infections can also cause polyarticular involvement, particularly in acute presentations. 1, 2

Bacterial Causes and Treatment

Staphylococcus aureus (Most Common)

• Oxacillin-susceptible: Nafcillin 1.5-2 g IV every 4-6 hours OR cefazolin 1-2 g IV every 8 hours is the preferred first-line therapy 3
• Oxacillin-resistant (MRSA): Vancomycin 15 mg/kg IV every 12 hours is the preferred agent 3
• Alternative options include daptomycin 6 mg/kg IV every 24 hours or linezolid 600 mg PO/IV every 12 hours 3
• Treatment duration is 4-6 weeks of pathogen-specific therapy 3

Neisseria gonorrhoeae (Disseminated Gonococcal Infection)

• Ceftriaxone is the recommended first-line therapy because penicillin-resistant strains are prevalent in many urban centers 2
• Presents as acute polyarticular syndrome with characteristic dermatitis and tenosynovitis 2
• Diagnostic clues include exposure history and type of rash 2

Streptococcus species (β-hemolytic)

• Penicillin G 20-24 million units IV every 24 hours (continuously or in 6 divided doses) is the preferred treatment 3
• Alternative: Ceftriaxone 1-2 g IV every 24 hours 3
• Treatment duration is 4-6 weeks 3

Gram-Negative Bacilli

Pseudomonas aeruginosa:

• Cefepime 2 g IV every 12 hours OR meropenem 1 g IV every 8 hours is preferred 3
• Alternative: Ciprofloxacin 750 mg PO twice daily or 400 mg IV every 12 hours 3
• Treatment duration is 4-6 weeks 3

Enterobacteriaceae:

• IV β-lactam based on in vitro susceptibilities is preferred 3
• Alternative: Ciprofloxacin 750 mg PO twice daily 3
• Treatment duration is 4-6 weeks 3

Salmonella species:

• Particularly important in patients with sickle cell disease 4
• Ceftriaxone provides adequate coverage 4

Enterococcus species

• Penicillin-susceptible: Penicillin G 20-24 million units IV every 24 hours OR ampicillin 12 g IV every 24 hours is preferred 3
• Penicillin-resistant: Vancomycin 15 mg/kg IV every 12 hours 3
• Treatment duration is 4-6 weeks 3

Viral Causes

Common Viral Pathogens

• Acute polyarticular syndromes are manifestations of certain viral infections in adults 2
• Detection of emerging arthritogenic viruses has changed the epidemiology of infection-related arthritis 1
• Viruses are increasingly recognized in the pathogenesis of chronic inflammatory arthritides 1

Mycobacterial and Fungal Causes

Chronic Infections

• Chronic monarticular or polyarticular processes are highly likely to be mycobacterial or fungal in etiology 2
• These frequently require appropriate culture of synovial tissue in addition to processing fluid 2
• Surgery may need to be combined with medical management for chronic mycobacterial or fungal infections 2

Diagnostic Approach

Critical Initial Steps

• Any patient with acute monarticular or new asymmetric polyarticular effusion should be suspected of having a bacterial process, especially with underlying joint disease 2
• Synovial fluid aspiration should be performed prior to initiating antibiotics 5
• Bacteriologic analysis by smear and culture is necessary for any new synovial effusion, as synovial fluid findings (leukocyte counts and glucose) may not be predictive of infection 2

Synovial Fluid Analysis

• Increasing leukocytosis is associated with higher likelihood of infectious cause, with patients commonly presenting with values greater than 50,000/μL 5
• Gram stain can provide immediate diagnostic information about the causative organism 6
• Nucleic acid amplification using polymerase chain reaction represents a newer diagnostic method 1

Treatment Principles

Surgical Management

• Joint drainage is always recommended in septic arthritis 5
• Options include daily needle aspiration, arthroscopy, or open surgical drainage via arthrotomy 5
• Surgical debridement is the mainstay of therapy and must be performed whenever feasible before or concurrent with antibiotic therapy 4

Duration and Monitoring

• Standard treatment duration for bacterial polyarthritis is 4-6 weeks of pathogen-specific intravenous or highly bioavailable oral antimicrobial therapy 3
• ESR and/or CRP should be monitored to guide response to therapy; a reduction of at least 25-33% from baseline after 4 weeks suggests lower risk of treatment failure 4
• Outpatient parenteral antimicrobial therapy (OPAT) is feasible with agents like ceftriaxone due to once-daily dosing 4

Critical Pitfalls to Avoid

• Do not delay synovial fluid aspiration and culture while waiting for imaging or laboratory results, as early recognition and treatment may prevent poor outcome 2
• Do not rely on synovial fluid cell counts alone to exclude infection; bacteriologic analysis is mandatory 2
• Do not use ceftriaxone empirically if MRSA is suspected; obtain cultures and use vancomycin until susceptibilities confirm methicillin-susceptible organisms 4
• Do not assume a single pathogen; polymicrobial polyarticular septic arthritis can occur with concurrent infection of separate joints by different bacterial pathogens 6
• For chronic infections, do not rely on synovial fluid culture alone; synovial tissue culture is frequently required for mycobacterial or fungal etiologies 2