s.aureus infections, 2006–2014 1231
MRSA SSTI incidence overall (−2.9%; P = .004) although not at any of the 3 sites of care. CA MRSA SSTI decreased significantly in incidence density
MRSA) SSTI incidence density did not change significantly among adults overall, children overall, and in adults and children combined. In children, no significant changes at any of the 3 sites of care were observed. In adults,HAMRSA SSTIs did not change significantly in outpatient or inpatient incidence density, but EDincidence density decreased (−10.7%; P=.035).
mssa sstis
MSSA SSTI incidence density increased significantly in both adults (+3.8% per year on average, P<.001) and children (+5.6%; P<.001) (Figure 2b). Among pediatric MSSA SSTIs, the only site of care with a significant increase in incidence density was among inpatients (+9.4%; P=.001). However, in adults, an increase in MSSA SSTI incidence density was observed in both outpatient (+4.6%; P=.001) and ED (+7.4%; P=.005) settings, but not in the inpatient setting. CA MSSA SSTI incidence density increased in both adults
(+4.6% per year on average, P=.001) and children (+6.1%; P<0.001). In adults, an increase in CA MSSA SSTIs among outpatients was observed (+7.4% per year on average; P=.008). In contrast, no significant change was observed in adult CA MSSA SSTIs in the inpatient or ED setting. In chil- dren, however, a significant increase in CA MSSA SSTI incidence density was observed in inpatients (+10.7%; P=.003) but not in the outpatient clinic or the ED. HA MSSA (including both HA and HACO MSSA) SSTIs
increased in incidence density among adults (+3.6% per year on average; P=.01); however, no significant change was observed in children. In adults, an increase in the inpatient (+3.3%; P=.03) and ED (+18.7%; P = .048) settings was observed for HA MSSA SSTIs. There was no significant change in adult outpatient HA MSSA SSTI incidence density. In children, no significant change was observed at any site of care.
Invasive MRSA Incidence
Invasive MRSA infection incidence density did not sig- nificantly change in adults or children overall or in any site of care, except for outpatient pediatric invasive MRSA infections, for which no calculation could be performed due to the small number of cases. In quarter 3 of 2007, a relatively high incidence density of invasive MRSA infections in children was detected. Because this quarter represented an outlier, analyses
in both children (−2.6% per year on average; P=.016) and adults (−3.6%; P=.003) (Figure 2a). In children, a decrease in CA MRSA SSTIs in outpatient (−7.8%; P=.02) and inpatient (−4.5%; P=.04) settings was observed, but not in the ED. In adults, CA MRSA SSTI incidence density significantly decreased only in the outpatient setting (−7.0%; P<.001). In all sites of care, HA MRSA (combining HA and HACO
performed for this quarter were excluded. Even with this quarter excluded, however, no significant change in pediatric invasive MRSA infections was observed.
Invasive MSSA Incidence
The incidence density of invasive MSSA infections did not significantly change among adults or children overall nor for adults or children at any specificsiteofcare.
Antimicrobial Susceptibilities of MSSA and MRSA
Table 3 shows susceptibility results for MRSA and MSSA SSTIs and bloodstream infections. Overall, MRSA blood isolates were more likely to be drug resistant than MRSA SSTI isolates. In contrast, MSSA isolates from blood and SSTIs exhibited similar resistance patterns. Table 3 also shows any significant changes in susceptibility to each of the tested non–β-lactam antibiotics. Erythromycin susceptibility was available for a subset of isolates. For MRSA SSTI isolates, there was a significant decrease in susceptibility to tetracycline, ciprofloxacin, and clindamycin from 2006 to 2014. ForMRSA andMSSAblood isolates, there was asignificant decrease in susceptibility only to tetracycline during this period. For MSSA SSTI isolates, there was a significant decrease in susceptibility to tetracycline and clindamycin.
discussion
At UCM in 2006–2014, while the incidence density of all MRSA infections decreased, overall MSSA incidence density did not change significantly in adults and children combined, which is consistent with our hypothesis. However, we found that the incidence of all MSSA infections in adults increased, yet it declined in children. Furthermore, in both children and adults, an increase in incidence of MSSA SSTIs was observed. As hypothesized, for children, compared with adults, a greater proportion of total S. aureus infections were SSTIs, both for MRSA and MSSA. Our study reports an increase in the incidence of MSSA infections in adults, which calls into question current approaches to preventing MSSA infections. Previous studies utilizing genotyping of MSSA showed that in-hospital MSSA transmission is unusual.32 However, an increase in MSSA infections may prompt a re-evaluation of the importance of horizontal infection control practices rather than vertical measures directed specifically toward MRSA control. Alternatively, if horizontal transmission is not responsible for an increase inMSSA infections, perhaps the increase is due to a change in MSSA strain virulence. Improvement in hand hygiene adherence is a strategy that may reduce MSSA trans- mission in healthcare facilities, particularly when patients with an MSSA infection are frequently present. CA MRSA SSTIs decreased in incidence among children and
adults, as did MRSA infections overall. These trends may reflect changes in the molecular epidemiology of MRSA or
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