JAMA：美国社区MRSA感染率处于下降之中

芝加哥–据7月4日刊《美国医学会杂志》JAMA上的一项研究披露，在对包括了9百多万名国防部非现役及现役军人所做的分析中，社区内起病的和医院内起病的耐甲氧西林金黄色葡萄球菌（MRSA）菌血症从2005年至2010年都有所下降，而社区内起病的皮肤和软组织MRSA的感染则在较为最近的时候有所下降。

根据文章的背景资料：“美国的侵入性MRSA感染的幅度及社区内起病的MRSA感染的出现都是有案可稽的。与美国平民人口中的社区内起病的MRSA感染的出现相平行的是，皮肤和软组织感染(SSTIs)已经成为美军中的一个重大的公共卫生问题。… 医院内起病的MRSA感染率据报道有所下降，但最近的社区内起病的金黄色葡萄球菌的感染率则较少有人知道。”

德克萨斯州萨姆-休斯敦堡圣安东尼奥军事医疗中心的Michael L. Landrum， M.D.及其同事开展了一项研究，旨在调查一个由美国各个地区的所有年龄组的人组成的一大群人中的社区内起病及医院内起病的金黄色葡萄球菌菌血症及SSTIs的发生率，以及其中MRSA所占的比例。该分析是由一项从2005年1月一直到2010年12月的对所有国防部TRICARE受益人的观察性的研究组成的。研究人员用病例数据库来发现并区分所有的，作为甲氧西林敏感性金黄色葡萄球菌（MSSA）或MRSA，以及社区内起病或医院内起病的感染（入院3天后收集的分离株）的，年度首次呈现阳性的金黄色葡萄球菌血液及伤口或脓肿培养物。

研究人员发现，从2005至2010年间，社区内起病及医院内起病的MRSA菌血症的年度发生率有所下降。同时，由MRSA所造成的社区内起病的SSTI的年度比例在下降至2010年时的52%之前于2006年时达到了62%的峰值。

文章的作者强调了这一研究的几个发现，其中包括医院内起病的MRSA菌血症发生率显著下降及社区内起病和医院内起病的MRSA菌血症发生率也都呈平行下降。社区内起病的MSSA菌血症的年度发生率也呈显著的下降。“然而，由于MRSA，社区内起病及医院内起病的金黄色葡萄球菌菌血症的比例都没有显著的改变，提示MRSA和MSSA菌血症发生率呈平衡性下降。对社区内起病的MRSA SSTIs来说，研究人员没有观察到年度发生率的显著的总体趋势，但由MRSA所致的社区内起病的SSTIs的比例则有了显著的下降。”他们补充说，在美军医疗系统中，金黄色葡萄球菌菌血症和SSTIs的负担仍然相当大，它凸显了要有成功预防和治疗策略的重要性。

doi:10.1001/jama.2012.7139
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Epidemiology of Staphylococcus aureus Blood and Skin and Soft Tissue Infections in the US Military Health System, 2005-2010

Michael L. Landrum, MD; Charlotte Neumann, MPH; Courtney Cook, MS; Uzo Chukwuma, MPH; Michael W. Ellis, MD; Duane R. Hospenthal, MD, PhD; Clinton K. Murray, MD

Context Rates of hospital-onset methicillin-resistant Staphylococcus aureus (MRSA) infections are reported as decreasing, but recent rates of community-onset S aureus infections are less known. Objectives To characterize the overall and annual incidence rates of community-onset and hospital-onset S aureus bacteremia and skin and soft tissue infections (SSTIs) in a national health care system and to evaluate trends in the incidence rates of S aureus bacteremia and SSTIs and the proportion due to MRSA. Design, Setting, and Participants Observational study of all Department of Defense TRICARE beneficiaries from January 2005 through December 2010. Medical record databases were used to identify and classify all annual first-positive S aureus blood and wound or abscess cultures as methicillin-susceptible S aureus or MRSA, and as community-onset or hospital-onset infections (isolates collected >3 days after hospital admission). Main Outcome Measures Unadjusted incidence rates per 100 000 person-years of observation, the proportion of infections that was due to MRSA, and annual trends for 2005 through 2010 (examined using the Spearman rank correlation test or the Mantel-Haenszel χ2 test for linear trend). Results During 56 million person-years (nonactive duty: 47 million person-years; active duty: 9 million person-years), there were 2643 blood and 80 281 wound or abscess annual first-positive S aureus cultures. Annual incidence rates varied from 3.6 to 6.0 per 100 000 person-years for S aureus bacteremia and 122.7 to 168.9 per 100 000 person-years for S aureus SSTIs. The annual incidence rates for community-onset MRSA bacteremia decreased from 1.7 per 100 000 person-years (95% CI, 1.5-2.0 per 100 000 person-years) in 2005 to 1.2 per 100 000 person-years (95% CI, 0.9-1.4 per 100 000 person-years) in 2010 (P = .005 for trend). The annual incidence rates for hospital-onset MRSA bacteremia also decreased from 0.7 per 100 000 person-years (95% CI, 0.6-0.9 per 100 000 person-years) in 2005 to 0.4 per 100 000 person-years (95% CI, 0.3-0.5 per 100 000 person-years) in 2010 (P = .005 for trend). Concurrently, the proportion of community-onset SSTI due to MRSA peaked at 62% in 2006 before decreasing annually to 52% in 2010 (P < .001 for trend). Conclusion In the Department of Defense population consisting of men and women of all ages from across the United States, the rates of both community-onset and hospital-onset MRSA bacteremia decreased in parallel, while the proportion of community-onset SSTIs due to MRSA has more recently declined.