**3.1.3 Previous antibiotic therapy**

False-negative results of microbiological cultures and even PCR tests have been reported in patients who received antibiotic therapy within 2 weeks prior to obtaining intra-articular sample material (Achermann et al., 2010). Furthermore, it is also suggested that perioperative antibiotic prophylaxis should be withheld if possible until samples for microbiological analysis have been obtained, but that the risk of false-negative sample results also should be weighed against the protective effect of pre-operative administration of antibiotic prophylaxis (Achermann et al., 2010; Engesaeter et al., 2003; Jämsen et al., 2009; Trampuz et al., 2007).
