NASAL CARRIAGE OF STAPHYLOCOCCUS-AUREUS AND EPIDEMIOLOGY OF SURGICAL-SITE INFECTIONS IN A SUDANESE-UNIVERSITY-HOSPITAL

Surgical site infections (SSI) due to Staphylococcus aureus among 256 male and 158 female patients (mean age, 28 years) undergoing elective surgery at the Soba University Hospital (Khartoum, Sudan) were studied . During an 11-month study period all patients were analyzed for nasal carriage of S. aureus at the time of admission. Follow-up of the deve lopment of SSI proceeded until I weeks after the operations. In additi on, nasal swabs were obtained periodically during the same period from 82 members of the staff. In order to discriminate autoinfection from cross infection, bacterial isolates were typed by random amplification of polymorphic DNA (RAFD), pulsed-field gel electrophoresis (PFGE) of DNA macrorestriction fragments, and restriction fragment length polym orphism analysis of the protein A and coagulase genes. Preoperative cu ltures revealed the presence of S, aureus in the noses of 98 patients (24%). The overall number of postsurgical wound infections in the enti re group was 57 (14%), 24 of which were due to S, aureus. Only 6 of th e 98 nasal S, aureus carriers suffered from wound infections by the sa me species. In these six cases the infecting strain could not be genet ically discriminated from the nasal inhabitant, substantiating autoinf ection. However, nasal carriage of S, aureus is not a significant risk factor for the development of SSI in this setting (6 of 98 patients w ith autoinfection versus 18 of 316 patients [414 - 98 patients],vith c ross infection; P = 0.81), most probably due to the fact that noncarri ers are at a significant and relatively large risk for acquiring an in dependent S, aureus SSI, The other S, aureus strains causing SSI showe d a high degree of genetic heterogeneity, demonstrating that it is not an epidemic strain that is causing the SSI, Among the staff personnel screened, 47.4% did not carry S, aureus in the nose at any time durin g the study period, whereas 13.2% persistently carried a single strain in the nose. Another 39.5% could be classified as intermittent carrie rs. When strains derived from staff personnel were genetically typed, it was demonstrated that most of the strains represented genetic varia nts clearly differing from the isolates causing SSI, On the other hand , possible cross colonization among staff personnel and even cross inf ection from staff personnel to patients or from patient to patient wer e demonstrated in some cases, but epidemic spread of a single strain o r a few clonally related strains of S, aureus could be excluded.