Hospital Preventive Medicine Service, Centre Hospitalier Universitaire Vaudois and University of Lausanne, Lausanne, Switzerland.
J Hosp Infect. 2011 Nov;79(3):202-5. doi: 10.1016/j.jhin.2011.04.021. Epub 2011 Jul 7.
According to molecular epidemiology theory, two isolates belong to the same chain of transmission if they are similar according to a highly discriminatory molecular typing method. This has been demonstrated in outbreaks, but is rarely studied in endemic situations. Person-to-person transmission cannot be established when isolates of meticillin-resistant Staphylococcus aureus (MRSA) belong to endemically predominant genotypes. By contrast, isolates of infrequent genotypes might be more suitable for epidemiological tracking. The objective of the present study was to determine, in newly identified patients harbouring non-predominant MRSA genotypes, whether putative epidemiological links inferred from molecular typing could replace classical epidemiology in the context of a regional surveillance programme. MRSA genotypes were defined using double-locus sequence typing (DLST) combining clfB and spa genes. A total of 1,268 non-repetitive MRSA isolates recovered between 2005 and 2006 in Western Switzerland were typed: 897 isolates (71%) belonged to four predominant genotypes, 231 (18%) to 55 non-predominant genotypes, and 140 (11%) were unique. Obvious epidemiological links were found in only 106/231 (46%) patients carrying isolates with non-predominant genotypes suggesting that molecular surveillance identified twice as many clusters as those that may have been suspected with classical epidemiological links. However, not all of these molecular clusters represented person-to-person transmission. Thus, molecular typing cannot replace classical epidemiology but is complementary. A prospective surveillance of MRSA genotypes could help to target epidemiological tracking in order to recognise new risk factors in hospital and community settings, or emergence of new epidemic clones.
根据分子流行病学理论，如果两种分离株在高度区分性的分子分型方法下具有相似性，则它们属于同一传播链。这在暴发中得到了证实，但在地方性情况下很少进行研究。当耐甲氧西林金黄色葡萄球菌 (MRSA) 的分离株属于地方性优势基因型时，无法确定人与人之间的传播。相比之下，罕见基因型的分离株可能更适合进行流行病学追踪。本研究的目的是在新发现的携带非优势 MRSA 基因型的患者中确定，从分子分型推断出的假定流行病学联系是否可以在区域监测计划的背景下替代经典流行病学。使用结合 clfB 和 spa 基因的双基因座序列分型 (DLST) 定义 MRSA 基因型。对 2005 年至 2006 年间在瑞士西部分离的 1268 个非重复 MRSA 分离株进行了分型：897 个分离株（71%）属于四个主要基因型，231 个（18%）属于 55 个非优势基因型，140 个（11%）为独特基因型。在携带非优势基因型的 231 名患者中，仅有 106 名（46%）发现明显的流行病学联系，这表明分子监测确定的簇数是可能通过经典流行病学联系怀疑的簇数的两倍。然而，并非所有这些分子簇都代表人与人之间的传播。因此，分子分型不能替代经典流行病学，但可以互补。对 MRSA 基因型的前瞻性监测有助于针对流行病学追踪，以识别医院和社区环境中的新危险因素，或新流行克隆的出现。
