Modification of patients' endogenous bacterial flora during hospitalization in a large teaching hospital in Naples.

The increasing attention addressed to methicillin-resistant staphylococci, vancomycin-resistant enterococci (VRE) and Extended Spectrum beta-Lactamases (ESbetaL)-producing enterobacteria is due to their etiologic role especially in nosocomial infections. In March 2001 we started an 8-month microbiological prospective surveillance of patients in the General Surgery, Orthopedic and Obstetric & Gynecology wards of the Azienda Universitaria Policlinico, 2nd University of Naples, Italy, to monitor the possible changes in endogenous flora during patients' hospital stay and the possible emergence of bacterial resistance. Data concerning antibiotic surgical prophylaxis (antimicrobial agent and duration) and length of hospitalization (pre- and post-surgery) were also collected. All patients underwent a microbiological screening by culturing nasal, pharyngeal and rectal swabs performed at admission and during hospitalization. Overall, 526 nasal swabs, 506 pharyngeal swabs and 482 rectal swabs were performed. Methicillin-resistant staphylococci were isolated from nasal swabs at admission in 2.1\% of patients and in 7.5\% of patients during hospitalization (day-14). VRE and ESbetaL-producing strains were isolated from rectal swabs in 1.9 and 4.7\% of patients, respectively, with no change during hospital stay. Nasal and pharyngeal flora significantly changed after 7-14 days of hospitalization, Gram-negative microorganisms being isolated more frequently following hospitalization. The authors conclude that excessive hospital stay duration, along with the inappropriate duration of surgical antibiotic prophylaxis could be important causes of bacterial flora modification.