Searching the Staphylococcal Superantigens: Enterotoxins A, B, C, and TSST1 in Synovial Fluid of Cases With Negative Culture Inflammatory Arthritis

BACKGROUND Accurate and rapid diagnosis of bacterial arthritis is not always possible in unvaccinated (Streptococcus pneumoniae and Haemophilus influenzae type B) children in Iran. OBJECTIVES Searching the staphylococcal superantigen (entrotoxin A, B, C and TSST1) in synovial fluid of cases with inflammatory arthritis. PATIENTS AND METHODS This cross sectional study was implemented in the pediatric and orthopedic wards, Rasoul Akram Hospital, Tehran, Iran (2008-2010) upon synovial fluid (SF) aspirated from 66 children (five months to 16 years; mean age 11 ± 3.8 years) with monoarthritis. Staphylococcal supperantigens (enterotoxins A, B, C, TSST1) were assessed by Enzyme-linked immunosorbent assay (ELISA) in synovial fluid of cases with inflammatory arthitis. Staphylococcal superantigens compared between cases with positive and negative Staphylococcus aureus culture (P < 0.05 was significant). RESULTS S. aureus was the most common cause of septic arthritis. Positive S. aureus culture in SF was reported in 10.6% (7/66) of the cases. Enterotoxin A was the least common type of superantigens found even in SF negative culture; 47% of the cases had one or more staphylococcal superantigens. Enterotoxin A was the least common type in SF; there was poor agreement between positive culture for S. aureus and presence of enterotoxins B, C, and TSST1 in SF, and intermediate agreement (KAPPA Index = 0.67) for enterotoxin A. CONCLUSIONS A possible role (%47) for staphylococcal toxins was defined even in SF negative cultures obtained from monoarthritis cases. Failure in isolation of organisms might be due to natural un-growth of microorganism in synovial fluid, and previous antibiotic usage or low technical methods. It could not be determined from the data obtained in the current investigation whether or not staphylococcal toxins (superantigens) play a pathogenic role without direct invasion of the organism. It is recommend to use complementary methods for searching the S. aureus superantigens in future studies.