The Effect of Organism Type on Surgically Managed Endocarditis

In what the authors described as first-of-its-kind, a new study reports that organism type plays a role in its impact on surgically managed left-sided infective endocarditis (IE).

“Infective endocarditis remains a vexing clinical condition, on the rise in North America,” said study author Judson B. Williams, MD, MHS, of Duke University in Durham, N.C., who presented the findings at the 65^th Annual Meeting & Exhibition of the Southern Thoracic Surgical Association.

Using the Society of Thoracic Surgeons (STS) database, information on adult patients with surgically managed IE between July 1, 2011, and June 30, 2016 was collected. Researchers compared causative microbiological organism, valve type (native vs. prosthetic), and right- (tricuspid) vs. left- (mitral, aortic) sided endocarditis.

The majority of operations were for left-sided IE (n = 20,033, 93%), with just 7% (n = 1,599) for right-sided IE. Right-sided IE patients tended to be younger (mean age 33), female, and Caucasian, Williams said. They also had fewer comorbidities, including hypertension and diabetes mellitus. In surgically managed left-sided endocarditis patients, the most common infecting organism was streptococcus (32%). Mortality was 6%.

“This served as the reference organism for comparisons, as strep was the most prevalent, and also associated with the best outcomes,” Williams said.

The second most common organism among left-sided patients was staphylococcus aureus (26%) and was associated with an 11% mortality rate (adjusted odds ratio [aOR] 1.41, P < 0.01). Fungal infections were the least common and only present in 1% but had the highest mortality rate (17%, aOR 2.89, P < 0.01). Staphylococcus aureus and fungal “both had 43% major morbidity,” Williams said, which included stroke, renal failure, and reoperation.

Enterococcus, culture negative, coagulase negative staphylococcus, and other organisms were present in 15%, 11%, 4%, and 11%, respectively, of left-sided IE patients. Culture negative patients had a 9% 30-day mortality rate (aOR 1.35); the rest of the organisms did not have a statistically significant 30-day mortality aOR. In right-sided patients, staphylococcus aureus was the most prevalent, presenting in 65% of patients.

Operative mortality rates were higher in left-sided prosthetic valve endocarditis patients than left-sided native valve endocarditis patients (12% vs 8%, P < 0.0001). Prosthetic valve on the left was associated with a 1.65 OR for mortality and 1.35 OR for major morbidity—both of which the researchers considered statistically significant compared to native valve patients.

For right-sided endocarditis patients, surgery had a lower mortality rate, and there was no significant difference in mortality rates for prosthetic valve and native valve endocarditis (5% vs 4%, P = 0.6). Organism type had a significant relative impact with respect to all model variables.

“Organism type is relatively quite impactful for fungal, staph aureus, and culture negative,” said Williams. “Streptococcus remains the most common organism, and fungus remains the most deadly; however, staph aureus is approaching strep in prevalence and approaching fungal in mortality and morbidity.” He added that “native versus prosthetic valves and microbiological organism type do not largely impact right-sided mortality, “perhaps due to younger patient population and generally more straight-forward operative approach on the right side.”

“Risk adjustment for operative outcomes in endocarditis may need to account for microbiological organism type, especially given that the affinity pathogen is now known to be identified in the vast majority of patients.”