Improvement of Long-Term Outcomes of MSSA Bacteremia With Formal Infectious Disease Consults

Highlighted Study:

Formal infectious diseases specialist consultation improves long-term outcome of methicillin sensitive Staphylococcus aureus bacteremia

Forsblom E, Frilander H, Ruotsalaineen E, Jarvinen A. Open Forum Infect Dis. 2019;6(12):ofz495. doi: 10.1093/ofid/ofz495

Staphylococcus aureus is a major cause of both health care-acquired and community-acquired infections ranging from skin and soft tissue infections to more invasive infections like bacteremia.¹ Staphylococcus aureus bacteremia (SAB) results in a significant morbidity and mortality. Mortality rates of SAB in the pre antibiotic era were 75-83%. These numbers have decreased, and recent data suggests that rates may have stabilized with a 30-day all-cause mortality rate of 20%.²

There is also some debate on what the best antimicrobial therapy is for treating MSSA bacteremia. Literature has shown us that β-lactams are superior to vancomycin for MSSA bacteremia,^3,4 but questions still remain on which β-lactam is preferred. Compounded with cefazolin and the inoculum effect,⁵ and the higher incidence of adverse effects with oxacillin,⁶ the treatment of MSSA bacteremia can become more complicated.

The 1 area that literature has shown benefit in are patients with bacteremia who have received formal infectious disease specialist (IDS) consultation. IDS consultation has shown improvement of clinical management of SAB by accelerating diagnostics and eradication of infection foci as well as the improvement of choice and duration of antimicrobial therapy. The role of IDS consultation on long-term outcomes has had very little literature or evaluation. Currently there are no studies on the effect of IDS formal consultation on long term outcomes beyond 1 year.

Forsblom and colleagues retrospectively reviewed 367 patients with MSSA bacteremia for 10 years post-infection.⁷ Patients were evaluated for risk for new bacteremia and outcomes. The primary outcome was mortality rate and occurrence of any new bacteremia during 1, 3 and 10 years. Exclusion criteria included patients who died within 90 days of IDS consultation, to decrease a possible bias that more severely ill patients with a poor prognosis would not receive formal IDS consultation.

In the retrospective analysis, 304 (83%) patients evaluated had a formal IDS consultation, where 63 (17%) received either an informal or no IDS consultation. No differences regarding age, gender, or bacteremia acquisition were observed between the 2 groups, there were also no differences in McCabe’s classification which predicts the likelihood of survival. The classification is based on a prognosis of rapidly fatal (<1 year), ultimately fatal (1-4 years) and non-fatal (>5 years).

Formal IDS consultation was associated with a reduced risk of new bacteremia from any pathogen at 1 and 3 years, and a trend towards lower risk was noticed at 10 years. Formal IDS consultation showed a decrease in mortality at 1, 3 and 10 years as compared to no formal IDS consultation (Table). When all prognostic parameters are considered, formal IDS consultation improved outcomes (HR, 0.42; 95% CI, 0.27-0.65; P < 0.001) and lowered risk for any new bacteremia (OR, 0.45; 95% CI, 0.23-0.88; P = 0.02) at 10 years.

Limitations noted by the authors include inherent risk of bias due to the retrospective design. Patients who received formal IDS consultation had fewer hematological malignancies, however the analysis was performed twice both including and excluding hematological malignancies, and the impact of IDS consultation was identical. A second concern was that patients with a poor prognosis may not have received formal IDS consultation which could have skewed the data. As mentioned previously, the exclusion of patients who died within 90 days was thought to have corrected this potential bias. A third possible limitation was that there may have been some issues with the antibiotics chosen, particularly the fluoroquinolone trovafloxacin, which was available during 1 of the time periods studied. A complete discussion can be found in the original article.

This study continues to grow the evidence that a formal IDS consultation can improve outcomes for patients with bacteremia. This could have possible ramifications for future updates of the Core Elements for an Antimicrobial Stewardship programs.⁸ As of now there is no formal requirement for formal IDS consultation for bacteremia, but as literature continues to show overall improvement in patient outcome with IDS consultation, one could envision it becoming a measurable action item. Until then, institutions should evaluate whether implementing automatic IDS consultation on patients with SAB should be adopted as local best practices. Additionally, institutions without ID services available may need to explore options for tele-services or other creative solutions to contract with IDS personnel.

References:

1. Magill SS, O’Leary E, Janelle SJ, et al. Emerging Infections Program Hospital Prevalence Survey Team. Changes in prevalence of health care-associated infections in U.S. hospitals. N Engl J Med 2018;379:1732-44. doi: 10.1056/NEJMoa1801550
2. Van Hal Sj, Jensen SO, Vaska, VL, et al. Predictors of mortality in Staphylococcus aureus bacteremia. Clin Microbiol Rev. 2012;25(2):362-86. doi: 10.1186/s12941-016-0122-8
3. Kim, SH, Kim KH, Kim HB, et al. Outcome of vancomycin treatment in patients with methicillin-susceptible Staphylococcus aureus bacteremia. Antimicrob Agents Chemother. 2008;52:192-7. doi: 10.1128/AAC.00700-07.
4. McDanel JS, Perencevich EN, Diekema DJ, et al. Comparative effectiveness of beta-lactams versus vancomycin for treatment of methicillin-susceptible Staphylococcus aureus bloodstream infections among 122 hospitals. Clin Infect Dis. 2015;61(3):361-7. doi: 10.1093/cid/civ308.
5. Miller WR, Seas C, Carvajal LP, et al. The cefazolin inoculum effect is associated with increased mortality in Methicillin-Susceptible Staphylococcus aureus bacteremia. Open Forum Infect Dis. 2018;5(6):ofy123 doi: 10.1093/ofid/ofy123.
6. Li J, Echevarria KL, et al. Comparison of cefazolin versus oxacillin for treatment of complicated bacteremia caused by Methicillin-Susceptible Staphylococcus aureus. Antimicrob Agents Chemother. 2014;58(9):5117-24. doi: 10.1128/AAC.02800-14
7. Forsblom E, Frilander H, Ruotsalainen, et al. Formal infectious diseases specialist consultation improves long-term outcome of Methicillin-sensitive Staphylococcus aureus bacteremia. Open Forum Infect Dis. 2019;6(12):ofz495 https://doi.org/10.1093/ofid/ofz495
8. US Department of Health and Human Services/CDC. Core Elements of Hospital Antibiotic Stewardship Programs. Atlanta, GA: CDC; 2019. https://www.cdc.gov/antibiotic-use/healthcare/pdfs/hospital-core-elements-H.pdf

Zimmer is an ID/Antimicrobial Stewardship pharmacist at CoxHealth in Springfield, MO. Drew enjoys fly-fishing, hunting, the St. Louis Cardinals and all things ID. You can find him on Twitter @zimrx17.*He is an active member of the Society of Infectious Disease Pharmacists.