Septic arthritis is a disabling and potentially life-threatening condition that requires prompt diagnosis and treatment. The most important risk factors are joint prosthesis, pre-existing joint disease and immunosuppressive drugs. The aim of our study therefore was to revaluate all septic arthritis cases discharged from our Rheumatologic Unit in the last 12 years, to assess the risk factors, the clinical and laboratory characteristics, the causative microorganisms and its possible increase in frequency.

The medical records of 42 consecutive patients with septic arthritis discharged from our Rheumatology Unit between January 1995 and December 2006 were reviewed. The patients ranged in age from 23 to 90 and there isn't gender predominance. Septic arthritis was diagnosed based on the finding of purulent material in the joint space and/or the isolation of a bacterial pathogen from joint fluid. Demographic data, risk factors, co-morbidity, clinical manifestations, time interval between symptoms onset and diagnosis, treatment and laboratory data including serum white blood cell count, erythrocyte sedimentation rate (ESR), C reactive protein (CRP), synovial white blood cells and culture results were analysed. We considered these parameters in the whole population and in two different age groups (< or =60, >60) and tried to determine if there was a change of microorganisms involved in septic arthritis during the years.

Of 42 patients, 47% were aged 60 and younger. Only 10 patients were admitted to our unit before 2001. A predisposing factor was recorded in 90,5% of cases: 15 patients had rheumatoid arthritis, 8 were diabetic, 6 had seronegative arthritis, 4 had a connective tissue disease, 8 patients had a prosthetic infection and 3 were subjected recently to arthrocentesis. We found that patients aged 60 and younger were more frequently affected by joint disease and had a synovial white blood cell count lower than patients older than 60. Staphylococcus aureus caused septic arthritis in 70% of cases before 2001, and only in 35,8 % after 2001. Also, after 2001, some infections were caused by more unusual pathogens, prevalently in patients treated with TNFa inhibitors. Instead Streptococcus infections were found only in patients aged 70 and older.

The incidence of bacterial arthritis has increased in the last six years and there was a modification of microorganisms involved, possibly related to a greater therapeutic aggressiveness. The increased frequency of joint disease and the use of immunosuppressive drugs in patients under the age of 60 could be responsible for a lower synovial white blood cell count in these patients.