Septic arthritis A painful, red, and swollen joint may have different causes. Septic arthritis is one of the most serious conditions and should be diagnosed and treated right away. In the native joint, an infection can damage the cartilage within the first 24 hours with impacts on joint function including lingering joint problems leading to possible future joint destruction. An interdisciplinary approach is essential for achieving optimal results. Most infections are caused by bacteria from the patient's own microbiome. In general, the incidence of native joint infections is growing, whether it is due to more appropriate diagnostics, or an actual increase cannot be determined at this point. In case of an acute infection, the patients usually describe a relatively short and acute period of pain, redness, and swelling of the affected joint. For diagnostic purposes the common blood serum laboratory work-up serves as a basis, complemented by puncture of the affected joint. Cell count and cell differentiation in the synovial liquid, microbiological and histopathological workup serve as gold standard in detecting septic arthritis. Septic arthritis lacks a distinctive presentation and other inflammatory conditions, like CPPD and gout must be considered. Prior to antibiotic therapy, joint lavage is the most important method to reduce bacterial load, leading to an improved outcome. Prognosis is determined by a swift diagnosis and initiation of therapy. The patient's comorbidities are significant, especially immunocompromising factors such as rheumatoid arthritis, diabetes or immunomodulating therapy. In case of a second focus of infection, chronic kidney disease or older age, patients are at greater risk for an inferior outcome.