Staphylococcus aureus, including community-acquired methicillin-resistant S. aureus, in a level III NICU: 2001 to 2008

Abstract

Objective: To determine epidemiology and clinical characteristics of infants with methicillin-susceptible (MSSA) and -resistant Staphylococcus aureus (MRSA) in a level III neonatal intensive care unit (NICU).

Study design: All NICU admissions (2001 to 2008) with any positive S. aureus culture were included as cases. Cases were further characterized as either colonized or infected with invasive disease.

Results: Four thousand three hundred four infants were admitted; 273 (6.3%) had at least one culture positive for S. aureus, including 198 with MSSA and 75 with MRSA. Invasive disease occurred in 23.2% of MSSA cases versus 29.3% MRSA (p = 0.298). Between the study periods 2001 to 2005 versus 2006 to 2008, the incidence of all MSSA cultures (colonization and invasive disease) decreased from 53.6 to 38.9/1000 admissions (p = 0.044), and that of MRSA increased from 13.7 to 24.77/1000 admissions (p = 0.010). The incidence of invasive MSSA (p = 0.49) and MRSA (p = 0.38) disease between the two periods remained similar. Infants with invasive MRSA versus MSSA had a longer duration of positive cultures (55 versus 19 days, p = 0.009). None of five available isolates collected prior to 2006 was characterized as USA300, but 11/21 isolates collected subsequently were USA300 (p = 0.053).

Conclusion: The incidence of MRSA (colonization and infection) nearly doubled during the study period coinciding with emergence of community-acquired MRSA USA300.