Final answer:
The most likely cause of red-tinged aspirated synovial fluid that contains pus is a bacterial infection. This condition, known as infectious arthritis, is confirmed through tests such as culture and antimicrobial susceptibility testing, and it typically requires antibiotic treatment.
Step-by-step explanation:
If aspirated synovial fluid is red tinged and contains pus, the most likely cause is a bacterial infection. When synovial fluid is aspirated and assessed, the presence of red tinge usually suggests bleeding within the joint, while pus indicates an infection. The direct microscopic evaluation and culture, along with antimicrobial susceptibility testing and polymerase chain reaction (PCR) analyses, confirm the presence of a potential pathogen.
Common treatments for infectious arthritis include administration of appropriate antimicrobial drugs such as ß-lactams for staphylococcal infections or third-generation cephalosporins for ß-lactam-resistant Neisseria infections. More chronic forms of arthritis, such as osteoarthritis or rheumatoid arthritis (RA), generally do not exhibit these acute signs of infection. Rheumatoid arthritis, for instance, is an autoimmune disease that can lead to joint inflammation and pain but isn't typically associated with the presence of pus in the synovial fluid.