Certain Staphylococcus aureus isolates are associated with changes in clinical presentation and severity of S aureus bacteremia, according to a study published in Clinical Infectious Diseases.
The syndrome of S aureus bacteremia has been considered fundamentally similar over time by clinicians, but this assumption has been brought into question by recent observations. Previous studies have drawn associations between an increased risk for various forms of infectious complications and specific bacterial genotypes. Further, there are several identified bacterial clones and types that are distinct for their virulence and ability to cause forms of infection. Therefore, this prospective, longitudinal study tested the hypothesis that temporal shifts in patient characteristics and in the genotype of S aureus bloodstream isolates are associated with changes in clinical presentation and severity of S aureus bacteremia.
In total, 2348 patients with monomicrobial S aureus bacteremia from an academic medical center in the United States were included. Each patient’s initial bloodstream S aureus isolate was genotyped. Using a linear regression, changes over time in both the patient and bacterial characteristics were estimated. Using multivariable regression models, associations between genotypes or clinical characteristics and complications were estimated.
Of the S aureus isolates obtained from the participants, 52% were methicillin susceptible. Researchers identified 411 distinct spa genotypes of S aureus, and also noted that despite 2 attempts, 3.6% of isolates could not be typed. Researchers reported that 54.2% of participants had an implantable foreign body of some type and this proportion increased by 0.96% annually throughout the 21-year study period (P =.002). In addition, throughout the study period, rates of metastatic complications significantly increased by 0.94% annually (P =.19). Numbers of people with comorbid conditions and rates of acquisition outside the hospital also increased.
Results demonstrated that genotypes of S aureus isolates showed a significant decline during the study period, including spa-CC012 (multi-locus sequence type [MLST] CC30), -CC004 (MLST CC45), -CC189 (MLST CC1), and -CC084 (MLST CC15). However, isolates of spa-CC008 (MLST CC8) increased 4-fold over the study period. Further, patients with S aureus bacteremia caused by spa-CC008 were significantly more likely to have metastatic complications in general, and more specifically abscesses, septic emboli, and persistent bacteremia. The USA300 variant of spa-CC008 was also independently associated with metastatic complications such as septic emboli and persistent bacteremia after adjusting for demographic, racial, and clinical variables. In addition, researchers highlighted that S aureus that were resistant to methicillin were primarily a result of the spa-CC002 genotype (68.7%).
Overall, the study authors concluded that, “Systemic approaches for monitoring complications of [S aureus bacteremia] and genotyping the corresponding bloodstream isolates will help identify the emergence of hypervirulent clones and likely improve clinical management of this syndrome.”
Souli M, Ruffin F, Choi SH, et al. Changing characteristics of Staphylococcus aureus bacteremia: results from a 21-year, prospective, longitudinal study [published online April 19, 2019]. Clin Infect Dis. doi:10.1093/cid/ciz112