Septic arthritis

Background

Gonococcal: Neisseria gonorrhoeae, more common in young, sexually active adults
Non-gonococcal bacterial:
- Staphylococcus aureus, in immunocompetent and immunocompromised people as well as those at risk for Staphylococcus aureus bacteremia; this is the most common causative organism overall
- Group B streptococci, more common in poorly-controlled diabetes
- Streptococcus pneumoniae, more common in patients with hyposplenia
- Enterobacteriaceae, especially if GI illness, or immunocompromised patients and those who inject drugs
- Pseudomonas, more common in diabetes, immunocompromised, trauma, or water exposures
- Aeromonas, more common after exposure to brackish water
- Salmonella, especially in patients with sickle cell disease or HIV
- Eikenella corrodens and Peptostreptococcus, especially if recent bite or other oral flora contamination
- Pasteurella multocida, after cat bite
- Capnocytophaga, after dog bite
- Mycoplasma hominis, with postpartum septic arthritis, recent genitourinary tract manipulation, and immunocompromise
Other:
- Mycobacterium tuberculosis and non-tuberculous mycobacteria (especially Mycobacterium chelonae and Mycobacterium fortuitum
- Fungal infections including Candida, Blastomyces dermatitidis, Cryptococcus, Coccidioides immitis, and Sporothrix schenckii
- Viral infections including HIV, hepatitis B virus, hepatitis C virus, parvovirus B19, and alphaviruses including chikungunya virus

Note: for fluid analysis, 1 cells/microL = 1,000,000 (1E6) cells/L; alternatively 1E9 cells/L = 1,000 cells/microL

Empiric: typically treated empirically with vancomycin and ceftriaxone empirically, followed by directed therapy

Treated with targetted antimicrobials
Duration is traditionally 4 weeks, including at least 2 weeks of parenteral antimicrobials
However, can do as short as 2 weeks for hand and wrist septic arthritis