Antibiotics and Cultures

Culture “yield” (isolation of infecting organism) is lower in patients who are receiving or have recently (within two weeks) received antibiotics.¹⁰⁵ This may be because elution of antibiotics into the joint fluid interferes with isolating the infecting organism by culture. Although, the exact “antibiotic-free” time needed to allow ”wash-out” of antibiotics from systemic circulation and the joint is not known, the work group has accepted two weeks as the minimum time required. One study showed that the false negative rate of cultures was significantly higher in patients who received antibiotics within two weeks of aspiration of a joint.¹⁰⁵