Bacterical contamination in bone transplant surgery: culture re-testing compared to clinical infection.

In the period from 1999 to 2003 bacterial contamination of explanted cadaver bones and tendons from the Regional Tuscan Tissue and Cell Bank was studied. During this period 1124 explants from 402 donors were taken, of which 311 donors whose heart was beating and from 91 whose heart was not beating. The bone explantation procedure followed a standardized protocol. Al the samples were explanted in the operation room by a team of two surgeons and a nurse during the first 24 hours after death. The protocol concerning the sterility of the explanting procedure was standardized and followed accurately. The bacteriological examination was performed immediately after the explantation and before the samples were treated with antibiotic solution. Three different tests were used: superficial microbiological swabs of the bone surface, one from the medullar canal and a small bone or soft tissue sample. The samples were inoculated immediately in culture medium and incubated for at least 10 days. From 1124 explanted samples 430 were contaminated: 99 with pathological bacteria such as Staphylococcus aureus, Enterococcus, Escherichia coli etc., 331 with nosocomial bacteria such as coagulase neg. Staphylococcus, Corynebacteria, etc. The samples that were contaminated with pathological bacteria were excluded from the study. The other contaminated group was re-processed and re-tested for contamination. The factors influencing the results of contamination were anatomical location of the explants and the experience of the surgical team. In contrast, the donor type (heart beating vs. heart not beating) did not play any role. From 1999 to 2003 the University Hospital of Careggi in Florence, Italy, used 721 explants from which 624 were retrieved from the Regional Tuscan Tissue and Cell Bank, 72 from foreign banks and 14 from another national bank. The explants from foreign banks were all re-tested according to our standards. Among those, 699 samples were sterile and 22 samples (3%) were contaminated. Seventeen (2.3%) of the 22 samples were contaminated with pathological bacteria with low morbidity and 5 (0.7%) with medium morbidity. Compared to the control group contamination of the explants retrieved from the Regional Tuscan Tissue and Cell Bank was 2.8%. However, the contamination of samples of an explant is not necessarily correlated with a true infection of the specimen. This study shows that factors such as retrieval techniques, contamination factors in the operating room and laboratory mistakes can cause false-positive contamination results. In fact, only three of 604 patients who were operated in major orthopaedic procedures using bone and soft tissue allografts developed clinical evidence of infection (0.5%). In conclusion, the infection rate of our allografts in this study is not higher than the standard infection risk of any other major orthopaedic procedure (0.5%).