2.5. Microbiological diagnosis of prosthesis infections

Microbiological samples can be obtained by aspiration of the prosthetic joint or during operation. The sensitivity of aspirated samples for culture has been poor, although it can be somewhat improved by sonication. Multiple organisms are often isolated in the samples, which may indicate polymicrobial infection, but also raises the possibility that one microorganism may be responsible for the infection and the other may be a contaminant. New diagnostic tools, such as PCR, tend to render the interpretation of the results even more difficult. However, multiple specimens for culture should be obtained from any suspected infection site, and the clinician should place the samples into transport media for anaerobic microorganisms. Multiple specimens will facilitate interpretation of the culture results. A concordant positive result for a particular microorganism from three specimens indicates infection. Additional information from the microbiology laboratory, such as massive growth in cultures and the resistance pattern of the pathogen, may help to suggest true infection. However, some cases remain unclear even after a review of all data available. The high likelihood of contamination precludes the routine use of microbiological culture for prosthesis-related infections without clinical signs or symptoms of infection, unless multiple specimens are taken. Nevertheless, some patients scheduled for routine revision do not present with signs or symptoms of infection, and the diagnosis of prosthesis-related infection is made exclusively based on intraoperative culture and histopathology. This applies specifically to patients with a suspected diagnosis of aseptic loosening of the prosthesis, who require careful workup. (Widmer 2001)