Staphylococcus aureus infections in US veterans, Maryland, USA, 1999-2008

Abstract

Trends in Staphylococcus aureus infections are not well described. To calculate incidence in overall S. aureus infection and invasive and noninvasive infections according to methicillin susceptibility and location, we conducted a 10-year population-based retrospective cohort study (1999-2008) using patient-level data in the Veterans Affairs Maryland Health Care System. We found 3,674 S. aureus infections: 2,816 (77%) were noninvasive; 2,256 (61%) were methicillin-resistant S. aureus (MRSA); 2,517 (69%) were community onset, and 1,157 (31%) were hospital onset. Sixty-one percent of noninvasive infections were skin and soft tissue infections; 1,112 (65%) of these were MRSA. Ten-year averaged incidence per 100,000 veterans was 749 (± 132 SD, range 549-954) overall, 178 (± 41 SD, range 114-259) invasive, and 571 (± 152 SD, range 364-801) noninvasive S. aureus infections. Incidence of all S. aureus infections significantly increased (p<0.001), driven by noninvasive, MRSA, and community-onset infections (p<0.001); incidence of invasive S. aureus infection significantly decreased (p<0.001).

Figure 1

Incidence per 100,000 veterans of Staphylococcus aureus infections by invasive and noninvasive (A), methicillin susceptibility (B), and onset (C), Veterans Affairs Maryland Health Care System, fiscal years 1999–2008. Solid line represents all S. aureus infections. MRSA, methicillin-resistant S. aureus; MSSA, methicillin-susceptible S. aureus; CO, community onset; HO, hospital onset.

Figure 2

Incidence per 100,000 veterans of skin and soft tissue infections (SSTIs) cause by methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-susceptible S. aureus (MSSA), Veterans Affairs Maryland Health Care System, fiscal years 1999–2008.