Final answer:
The first step in diagnosing septic arthritis involves aspirating synovial fluid from the affected joint for evaluation and culture to identify the causative organism, with Staphylococcus aureus being the most common pathogen.
Step-by-step explanation:
First Step in Diagnosing Septic Arthritis The first step in diagnosing septic arthritis—also known as infectious arthritis—in a patient (pt) involves the aspiration of synovial fluid from the affected joint. This procedure is crucial in identifying the causative organism responsible for the infection. Once the synovial fluid is obtained, several tests are carried out, including direct microscopic evaluation, culture, antimicrobial susceptibility testing, and polymerase chain reaction (PCR) analyses. These tests help in determining the appropriate antimicrobial therapy.
Staphylococcus aureus is often the most common bacterium causing both septic arthritis and osteomyelitis, especially in adults and young children. After identifying the pathogen through culture and susceptibility testing, treatment typically involves the administration of antimicrobials like ß-lactams such as oxacillin and cefazolin for staphylococcal infections, or third-generation cephalosporins for ß-lactam-resistant strains.
Accurate and timely diagnosis is essential because approximately 40% of patients with nongonnococcal infectious arthritis may suffer permanent joint damage, and mortality rates range from 5% to 20%, with even higher rates in the elderly population.