infection control & hospital epidemiology october 2017, vol. 38, no. 10 original article
S. aureus Infections in Chicago, 2006-2014: Increase in CA MSSA and Decrease in MRSA Incidence
M. Ellen Acree, MD;1,2 Ethan Morgan, BS;3 Michael Z. David, MD, PhD1,2,3
objective. To examine trends in Staphylococcus aureus infections in adults and children at a single academic center in 2006–2014. design. Retrospective cohort study. setting. Inpatient, outpatient, and emergency department settings in a private, tertiary referral center. patients. Patients with an infection culture that grew S. aureus in January 1, 2006, through March 31, 2014.
methods. The first isolate per year for each patient was classified as community-associated (CA-), healthcare-associated (HA-), or HA-community–onset S. aureus. The incidence density of S. aureus, methicillin-susceptible S. aureus (MSSA), and methicillin-resistant S. aureus (MRSA) infections were calculated per quarter year.
results. Overall, 5,491 MRSA and 5,398 MSSA isolates were included. MRSA infections decreased by an average of 5.2% annually (P<.001). MRSA skin and soft-tissue infection (SSTI) incidence density decreased in adults (−3.5%; P<.001) and children (−2.9%; P=.004). MSSA infections at all anatomic sites increased by an average of 1.9% annually (P=.007) in adults and decreased 5.1% annually (P<.001) in children. MSSA SSTI incidence density increased in adults (+3.8%; P<.001) and children (+5.6%; P<.001). For MRSA and MSSA SSTI isolates, susceptibility to tetracycline and clindamycin decreased significantly.
conclusions. In 2006–2014, MRSA SSTI incidence decreased among children and adults. MSSA SSTI incidence density increased in children and adults, suggesting that current empiric SSTI treatment recommendations may not be optimal. Adults experienced an overall increase in MSSA infections, which may prompt consideration of the need for horizontal infection control practices to decrease MSSA infection risk.
Infect Control Hosp Epidemiol 2017;38:1226–1234
Staphylococcus aureus is among the most common pathogens causing human skin and soft-tissue infections (SSTIs), bloodstream infections, bone and joint infections, and others.1 Methicillin-resistant Staphylococcus aureus (MRSA) strains of S. aureus are resistant to nearly all β-lactam antibiotics. Before the late 1990s, MRSA caused disease in individuals
with healthcare exposure.2 However, the epidemiology of MRSA and S. aureus changed dramatically in the first decade of the 2000s with the emergence of genotypically novel community-associated (CA) MRSA strains.3–12 A study from the University of Chicago Medicine (UCM) demonstrated an increase in methicillin resistance among S. aureus clinical
isolates from 13%to 28%between 1986 and 2000.13 CAMRSA first had an epidemiological impact in previously healthy children and later, in adults.7,14 The older, genotypically distinct MRSA strains identified in hospitals that rarely cause infections in healthy people are known as healthcare-associated (HA)
MRSA. Since 2004, CA and HA MRSA strains have caused infections originating in both community and healthcare set- tings.15–17 At UCM, the prevalence of CA MRSA infections among all MRSA infections increased from 36.5% to 62.2% between 2004–2005 and 2008.8 As the incidence of MRSA infections increased, CA MRSA did not simply replace CA methicillin-susceptible S. aureus (MSSA), but instead added to the overall S. aureus disease burden.18,19 Multiple studies have demonstrated an epidemic of CA
MRSA infections from the late 1990s to the early 2000s3,5,10,12,20–29 in children 10,21,24,28 and adults.12,20,21 CA MRSA is most likely to cause SSTIs,4,5,10,22,27,29 particularly in children,5 but an increase in CA MRSA invasive infections in the United States was also recorded in the early 2000s.9 Many US hospitals isolate patients with MRSA colonization
or infection and practice active surveillance of patients for MRSA colonization in intensive care units. However, the same
Affiliations: 1. Department of Medicine, Public Health Sciences, University of Chicago, Chicago, Illinois; 2. Department of Pediatrics, Public Health
Sciences, University of Chicago, Chicago, Illinois; 3. Department of Public Health Sciences, University of Chicago, Chicago, Illinois. PREVIOUS PRESENTATION:The results of this studywere presented in a poster presentation at IDWeek 2016 inNewOrleans, Louisiana, onOctober 9, 2016, poster number 1116.
© 2017 by The Society for Healthcare Epidemiology of America. All rights reserved. 0899-823X/2017/3810-0013. DOI: 10.1017/ice.2017.177 Received March 22, 2017; accepted July 11, 2017
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