Endocarditis is a common complication in Staphylococcus aureus bacteremia (SAB). We compared risk factors, clinical manifestations, and outcome in a large, prospective cohort of patients with S. aureus endocarditis in injection drug users (IDUs) and in nonaddicts.
Four hundred and thirty consecutive adult patients with SAB were prospectively followed up for 3 months. Definite or possible endocarditis by modified Duke criteria was found in 74 patients: 20 patients were IDUs and 54 nonaddicts.
Endocarditis was more common in SAB among drug abusers (46%) than in nonaddicts (14%) (odds ratio [OR], 5.12; 95% confidence interval [CI], 2.65├óÔé¼ÔÇ£9.91; P < 0.001). IDUs were significantly younger (27 ├é┬▒ 15 vs 65 ├é┬▒ 15 years, P < 0.001), had less ultimately or rapidly fatal underlying diseases (0% vs 37%, P < 0.001) or predisposing heart diseases (20% vs 50%, P = 0.03), and their SAB was more often community-acquired (95% vs 39%, P < 0.001). Right-sided endocarditis was observed in 60% of IDUs whereas 93% of nonaddicts had left-sided involvement (P < 0.001). An extracardiac deep infection was found in 85% of IDUs and in 89% of nonaddicts (P = 0.70). Arterial thromboembolic events and severe sepsis were also equally common in both groups. There was no difference in mortality between the groups at 7 days, but at 3 months it was lower among IDUs (10%) compared with nonaddicts (39%) (OR, 5.73; 95% CI, 1.20├óÔé¼ÔÇ£27.25; P = 0.02).
S. aureus endocarditis in IDUs was associated with as high complication rates including extracardiac deep infections, thromboembolic events, or severe sepsis as in nonaddicts. Injection drug abuse in accordance with younger age and lack of underlying diseases were associated with lower mortality, but after adjusting by age and underlying diseases injection drug abuse was not significantly associated with mortality.
Bacteremic infections caused by Staphylococcus aureus have been reported with increasing frequency, and it has emerged as a leading cause of infective endocarditis (IE) in many regions of the world [1-3]. Endocarditis has been observed in 11% to 35% of S. aureus bacteremias (SAB) attributable to different sets of diagnostic criteria [4-6]. S. aureus endocarditis is associated with higher occurrence of extracardiac deep infections due to metastatic spread, thromboembolic complications, and a high mortality compared with IE caused by other pathogens [1,2].
The incidence of endocarditis has not been changed during the past two decades [7,8] but classic risk factors such as rheumatic heart disease are being replaced by new groups, including injection drug users (IDUs), elderly patients with degenerative valve disease, patients with intravascular catheter or prosthetic valve, and nosocomial acquisition [2,3,8]. One of the reasons for increased incidence of S. aureus in IE is injection drug abuse [9-11]. Colonization with S. aureus, HIV-related immunosuppression, female sex, increasing injection drug use frequency, and a history of previous IE are associated with a higher risk for endocarditis [11,12].
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