Final answer:
Septic arthritis in the elderly involves a bacterial joint infection, commonly caused by Staphylococcus aureus, which requires medical diagnosis and treatment with antimicrobial drugs, although prognosis may be poor with high risk of mortality and joint damage.
Step-by-step explanation:
Septic arthritis in the elderly, such as in a 70-year-old nun, is a condition characterized by a bacterial infection within the joint, leading to inflammation and joint pain. This ailment is more common among those with weakened immune systems.
The most common bacterium causing both septic arthritis and osteomyelitis is Staphylococcus aureus. Diagnosis involves aspiration of synovial fluid and subsequent laboratory evaluations, including culture and polymerase chain reaction (PCR) analysis.
Treatment usually involves administration of antimicrobial drugs identified by susceptibility testing, but prognosis can be poor, especially for elderly patients, with risks of permanent joint damage and mortality rates between 5% to 20%.