Introduction of an integrated infection control program in an ICU: effects on epidemiology and antimicrobial resistance of Staphylococcus aureus

Background

Extensive use of antibiotics is responsible for the emergence of multiresistant strains, in the clinical setting. In our institution a profound remodelling of antibiotic prescription policy and implemented procedures to control cross-patient transmission were introduced in the first quarter of 2004, in response to an outbreak of Acinetobacter baumanii (AB). In this study we reported the effects induced by this new infection control program on the frequency of isolation of Staphylococcus aureus (SA) and its antibiotic resistance profile.

Methods

From January 2004 to April 2004 a new infection control program was instituted to contain an outbreak of AB. The key features of this approach consisted of the introduction of surveillance cultures, in an extensive use of microbiological sampling to guide therapy, a restricted antibiotic prescription policy (limited prophylaxis, selection of drugs on the basis of microbiological assays, early discontinuation of antimicrobials at clinical resolution, de-escalation therapy, restricted formulary), and VAP containing measures/devices (extended use of individual protection garments, controlled hand-washing procedures). The infection control program has remained operative after the resolution of the outbreak. The impact of the program on the frequency and sensibility of SA was evaluated for a 12-month period (period A from May 2004 to April 2005). The 12 months preceding the introduction of the program were considered a historical control period (period B from January 2003 to December 2003). The incidence of methicillin-sensitive SA (MSSA) and of methicillin-resistant SA (MRSA), the consumption of vancomycin and oxacillin, demographic data of admitted patients and outcome measures (ICU LOS and ICU mortality) were evaluated in the two periods. Statistical analysis: Student's t test, Mann-Whitney U test and chi-squared test.

Results

In period A more trauma patients and less surgical patients were admitted to the ICU. The SAPS II was significantly higher in period A. No difference in outcome measures was reported. In period A, a significant increase of MSSA (P = 0.009) and a significant decrease of MRSA (P = 0.03) were reported. Due to this epidemiological modification the consumption of oxacillin has noticeably increased, in association with a significant reduction of vancomycin consumption (P = 0.04).

Conclusion

The integrated infection control program introduced for the containment of an AB outbreak has resulted in profoundly affecting the microbiological environment of the ICU. In particular, it has significantly reduced the occurrence of MRSA. The increase in methicillin sensitivity of SA improved the use of oxacillin in place of vancomycin, with potentially favourable effects on costs. The finding that a different prevalence of trauma and surgical patients has occurred in the two study periods is a potentially confounding variable. Nevertheless, the higher severity of patients admitted in period A not being associated with an increase in mortality and LOS seems to confirm the positive effects of the renewal introduced.