s.aureusinfections, 2006–2014 1233 table 3. Continued
Gentamicina No.
Year 2010
2011 2012 2013
2014, Q1
(% susceptible) 62 (100.0)
59 (100.0) 65 (100.0) 77 (100.0) 18 (100.0)
Erythromycin No.
(% susceptible) 44 (71.0)
44 (74.6) 51 (78.5) 56 (72.7) 12 (66.7)
SSTI, skin and soft tissue infection. aNo resistant isolates were observed for gentamicin. bSignificant decrease (P<0.05).
perhaps population-wide herd immunity to USA300 MRSA or another strain. Changes in HA MRSA incidence may reflect the efficacy of infection control procedures at UCM. Previous literature suggested that the 15-year-long wave of
CA MRSA activity in the United States7 peaked and started to decline by 2010.6,30 In both children and adults, an observa-
tional study of the Department of Defense TRICARE bene- ficiaries showed that the proportion of community-onset SSTIs caused by MRSA decreased from 62% in 2006 to 52% in 2010 (P<.001).6 Our study shows a similar trend continuing up to early 2014; as a proportion of MRSA, infections that were CA MRSA decreased significantly from 2006 to 2013, suggesting a reversal of the massive increase in CA MRSA proportion in the previous decade.7 In adults, MSSA and MRSA incidence densities exhibited
opposing trends at UCM from 2006 to 2013. While MRSA infection incidence density decreased, MSSA infection inci- dence density in adults increased on average by nearly 2% per year, which had not been demonstrated previously. In both adults and children, CA MRSA SSTIs significantly
declined during the study period, which is congruent with pre- vious findings.6 In contrast,MSSA SSTI incidence density rose in both children and adults at UCM. This finding may have important implications for empiric SSTI treatment because MSSA infections are preferably treated with a β-lactam antibiotic. Our results suggest that effective empiric antibiotic choices
may continue to narrow because both MRSA and MSSA SSTI and blood isolates are following a trend toward increasing resistance to orally available agents. Our study has certain limitations. We did not account for
changes that may have occurred in the practice of sending bacterial cultures from sites of infection at UCM during 2006– 2014. Additionally, data were not available on patient stays in long-term-care facilities; therefore, our criteria differed from CDC criteria for HA, HACO, and CA S. aureus infections. However, individuals who stayed in a long-term-care facility within the previous year likely had another risk factor that would classify them as being healthcare-exposed. Also, the
automated D-test after December 2008 was performed on clindamycin-susceptible isolates with erythromycin resistance or intermediate erythromycin susceptibility. In contrast, the earlier-used, manual D-test was only performed only on erythromycin-resistant isolates. Therefore, inducible clin- damycin resistance may have been more frequently detected after the change to the automated D-test. Finally, without medical record reviews, we were unable to exclude all S. aureus cultures obtained from sites of colonization. However, we did exclude S. aureus isolates that were explicitly obtained to assess for colonization. In conclusion, at UCM in 2006–2013, MRSA infection incidence decreased. However, we demonstrated an unantici- pated increase in MSSA infection incidence in adults overall and specifically in CA MSSA SSTIs in both adults and children. These findings may inform future choices for empiric antibiotic selection. The increased incidence of MSSA infec- tions in adults may support the enhancement of horizontal infection control practices to prevent MSSA transmission or infection resulting from auto inoculation. Future surveillance for trends in MRSA and MSSA infections is needed to develop infection control policies and to optimize choices for empiric therapy for pediatric and adult S. aureus infections.
acknowledgments
Financial support: M.Z.D. received grant support from the National Institute of Allergy and Infectious Diseases at the National Institutes of Health (grant no. K23 AI095361). Potential conflicts of interest: All authors report no conflicts of interest
relevant to this article. Address correspondence to M. Ellen Acree,MD, 2122 Dewey Ave, Evanston,
IL 60201 (
ellenacree@gmail.com).
references 1. Lowy FD. Staphylococcus aureus infections. N Engl J Med 1998;339:520–532.
MSSA Blood Isolates (n=578) Rifampin No.
(% susceptible) 62 (100.0)
59 (100.0) 65 (100.0) 77 (100.0) 18 (100.0)
Tetracyclineb No.
(% susceptible) 62 (100.0)
58 (98.3) 62 (95.4) 74 (96.1) 17 (94.4)
Ciprofloxacinb No.
(% susceptible) 57 (91.9)
58 (98.3) 62 (95.4) 71 (92.2) 17 (94.4)
Clindamycinb No.
(% susceptible) 47 (75.8)
50 (84.8) 53 (81.5) 65 (84.4) 14 (77.8)
NOTE. MSSA, methicillin-susceptible Staphylococcus aureus; MRSA, methicillin-resistant Staphylococcus aureus; Q1, first quarter of the year;
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