An active microbiological surveillance project at an Italian teaching hospital: microbial isolates, recent epidemiological trends, major clinical concerns, and antimicrobial susceptibility rates during a four-year period.

A microbiological surveillance program is currently performed at our tertiary-care teaching hospital. The temporal trend of microbial isolates from patients admitted during four calendar years (2004 to 2007) was analyzed according to the main bacterial and fungal culture organisms. The same pathogens isolated more than once from the same patient within one month were considered only once. On the whole, the main pathogen group remained that of Enterobacteriaceae (6,608 isolations out of 19,666: 33.6%, with Escherichia coli found in 60-75% of cases), with no significant difference over time. Staphylococci (4,150 isolates), and enterococci (3,276 isolates) were the two largest groups after Enterobacteriaceae, but staphylococci significantly declined during the four-year period (p .001), mainly due to progressively reduced isolation of coagulase-negative staphylococci. By contrast, a slight increase in enterococci occurred (p .05). Based on the frequency of isolation, Gram-negative oxidase-positive organisms accounted for 2,109 episodes, followed by other aerobic Gram-positive organisms other than Staphylococci-Enterococci (613 isolates), and anaerobes (583 isolates): no significant variations occurred over time for these last microbial groups. With regard to Gram-negative oxidase-negative microorganisms (567 isolates), non-beta-haemolytic streptococci (464 cases) and beta-haemolytic streptococci (260 isolates), a significant reduction of frequency occurred from 2004 to 2007 (p.05 to p.001). Finally, fungal infections accounted for 1,036 overall episodes, in over 80% of cases represented by Candida spp. Prospective microbiological monitoring is expected to contribute significantly to our knowledge of local epidemiological figures and antimicrobial sensitivity profile of hospital infections, and plays a major role in selecting both treatment and chemoprophylaxis schedules, especially on a local-regional basis. Although the major causative agents of in-patient infections remain Enterobacteriaceae, a significant decline in coagulase-negative Staphylococci, all Streptococci, and Gram-negative oxidase-negative organisms occurred over the four-year period, while Enterococci showed a mild increase over time.