Impact of Allergy Status on Outcomes in Methicillin-Susceptible Staphylococcus aureus Bloodstream Infections (MSSA BSI)

Background: Beta-lactams (BL) are the antibiotics of choice for MSSA BSI. Despite widespread BL allergy reporting, true BL allergies are uncommon. It is unclear if a reported BL allergy adversely affects optimal treatment and outcome of MSSA BSI.

Methods: IRB approved, retrospective matched cohort study of patients with MSSA BSI with and without a BL allergy from 1/2014 to 12/2015 matched 1:3 by time and severity (intensive care unit status). Data collected: patient, allergy, and infection characteristics, antibiotic use, outcomes. Primary endpoint: proportion of patients who received optimal therapy, defined as antistaphylococcal BL. Bivariate and multivariate regression were utilized to identify characteristics associated with receipt of optimal therapy.

Results: 212 patients included: 53 with BL allergy and 159 without BL allergy. There were no significant differences in baseline or infection characteristics. Among BL allergic patients: 26 (49%) had an immune mediated reaction, 8 (15%) had a reaction that was intolerance and not allergy, and 19 (36%) had an unspecified reaction. Of 53 allergic patients, desensitization occurred in one patient; allergy consults were completed for 13% of patients. Optimal antibiotics were given to 135 patients without a BL allergy and 37 patients with a BL allergy (85% vs. 70%, P=0.015). Nafcillin or cefazolin was the optimal antibiotic used in 95% of patients. Median time to optimal antibiotics was 29 hours for both groups (P=0.64). No differences were found in clinical cure (79% vs 81%, P=0.76) or mortality (19% vs 18%, P=0.84). Infectious disease consults were more common among BL allergic (89% vs 75%, P=0.04), and were associated with an increased usage of optimal antibiotics (68% vs 13%, P<0.001), as seen in Table 1.

Conclusion: Patients with a documented BL allergy were less likely to receive optimal antibiotics for MSSA BSI. Patient outcomes may be improved with routine use of infectious disease consult to optimize therapy in patients who report BL allergies.

Table 1. Characteristics associated with optimal antibiotics	n, % Total population	Unadjusted OR 95% CI	Adjusted OR 95% CI
Beta-lactam allergy	53 (25)	0.41 (0.2-0.85)	0.3 (0.1-0.6)
ID consult	167 (79)	4.4 (2.1-9.3)	6.1 (2.7-13.9)
Immunosuppressed	25 (12)	2.9 (0.66-1.3)	2.9 (0.6-13.8)