Changing Characteristics of Staphylococcus aureus Bacteremia: Results From a 21-Year, Prospective, Longitudinal Study

Abstract

Background: We conducted a longitudinal study to evaluate changes in the clinical presentation and epidemiology of Staphylococcus aureus bacteremia (SAB) in an academic, US medical center.

Methods: Consecutive patients with monomicrobial SAB were enrolled from January 1995 to December 2015. Each person's initial bloodstream S. aureus isolate was genotyped using spa typing. Clonal complexes (CCs) were assigned using Ridom StaphType software. Changes over time in both the patient and bacterial characteristics were estimated with linear regression. Associations between genotypes or clinical characteristics and complications were estimated using multivariable regression models.

Results: Among the 2348 eligible participants, 54.2% had an implantable, foreign body of some type. This proportion increased significantly during the 21-year study period, by 0.96% annually (P = .002), as did comorbid conditions and acquisition outside of the hospital. Rates of any metastatic complication also significantly increased, by 0.94% annually (P = .019). Among the corresponding bloodstream S. aureus isolates, spa-CC012 (multi-locus sequence type [MLST] CC30), -CC004 (MLST CC45), -CC189 (MLST CC1), and -CC084 (MLST CC15) all significantly declined during the study period, while spa-CC008 (MLST CC8) significantly increased. Patients with SAB due to spa-CC008 were significantly more likely to develop metastatic complications in general, and abscesses, septic emboli, and persistent bacteremia in particular. After adjusting for demographic, racial, and clinical variables, the USA300 variant of spa-CC008 was independently associated with metastatic complications (odds ratio 1.42; 95% confidence interval 1.02-1.99).

Conclusions: Systematic approaches for monitoring complications of SAB and genotyping the corresponding bloodstream isolates will help identify the emergence of hypervirulent clones and likely improve clinical management of this syndrome.

Keywords: spa typing; spa-CC008; MRSA; USA300; clonal complex.

Figure 1.

Clinical characteristics of the study population that exhibited a significant trend over the study period. Lines represent the proportion of patients with a history of diabetes mellitus, corticosteroid use, transplantation, neoplasm, or prosthetic device(s).

Figure 2.

Annual distribution of all metastatic complications of SAB and of abscesses, vertebral osteomyelitis, septic emboli, and persistent bacteremia. Only metastatic complications with a significant trend are shown. Abbreviation: SAB, Staphylococcus aureus bacteremia.

Figure 3.

A, Annual distribution of CC causing SAB in our institution over the 21-year study period. USA300 clonal type is shown as hatched area within spa-CC008. Spa-CC012 corresponds to MLST CC30, -CC002 to MLST CC5, -CC004 to MLST CC45, -CC008 to MLST CC8, and -CC084 to MLST CC15. For other CCs refer to Supplementary Table 3. B–D, Distribution of predominant CCs, stratified by methicillin susceptibility. Abbreviations: CC, clonal complexes; MLST, multi-locus sequence typing; MRSA, methicillin-resistant Staphylococcus aureus; MSSA, methicillin-susceptible Staphylococcus aureus; SAB, Staphylococcus aureus bacteremia.