Research suggests that clinical characteristics of MRSA can differ by genotype. From March 2009 through February 2010, all MRSA isolates from seven community hospitals and many isolates from a tertiary care hospital in Ohio were prospectively collected for molecular characterization. Staphylococcal protein A (spa) typing was performed on the majority of collected isolates. This analysis explored the relationship between spa type assignment and MRSA clinical manifestation, comparing bloodstream infections to skin and soft tissue infections.
MRSA manifestation and spa type were the variables of interest in this study. Any spa-typed isolate from a primary or secondary bacteremia was included in the MRSA bacteremia group. Any spa-typed isolate from a skin and soft tissue specimen was included in the MRSA skin and soft tissue group. Any spa type that comprised at least 5% of all isolates was treated as its own spa category. Any spa types comprising less than 5% of all isolates were grouped into an “Other spa types” category. Associations between spa type and clinical manifestation were evaluated using Pearson’s chi-square test and standardized adjusted residuals. A multivariable logistic model was built to further evaluate this association.
spa typing was performed on 298 bacteremia isolates and 398 skin and soft tissue isolates. Most isolates were categorized into three spa types (spa 1(t008), spa 2(t002) and spa 3(t037)). Bacteremia isolates were 22.2% spa 1, 45.3% spa 2, 12.1% spa 3 and 20.5% other spa types. Skin and soft tissue isolates were 59.6% spa 1, 13.3% spa 2, 3.1% spa 3, and 23.5% other spa types. After adjusting for important confounders, the mean log odds of a bacteremia for the spa 1 group was 0.456 lower than the than the weighted grand mean log odds of bacteremia for all groups. This difference was significant at p=0.0014. Additionally, the mean log odds of bacteremia for the spa 2 group was 0.773 higher than the weighted grand mean log odds of bacteremia for all groups. This difference was significant at p<0.0001.
This analysis indicates that molecular genotypes may be independently associated with clinical characteristics of MRSA. Further virulence factor studies may better clarify these associations.
S. H. Wang, None
K. Stevenson, None