1093. Bypassing Penicillin Skin Testing in favor of Direct Oral Challenge: A Pharmacy-driven Inpatient Program

Background Patient interview, penicillin skin testing (PST) and/or an oral challenge can be used to evaluate penicillin allergies. Programs favor PST prior to oral challenge, but there is interest in bypassing PST and directly oral challenging for logistical and financial reasons. Data on the safety and efficacy of a direct challenge in the inpatient setting when the index reaction is moderate to severe (e.g. swelling of throat, angioedema, anaphylaxis) is lacking. Methods Adult patients (≥18 years) admitted with a penicillin allergy were evaluated for eligibility between September 2019 and June 2021. Pregnant patients were excluded, while critically ill patients and those on anti-histamine medications were evaluated if clinical need was high. Institutional protocols allowing for patients to be challenged without PST if reaction was more than 10 years ago were used. Data collected included the number of patients challenged and delabeled, number of patients who had moderate to severe index reactions, number of patients who were relabeled without cause, and number of patients who declined further testing. Results Two hundred twenty-five patients were evaluated; 11 patients declined testing. Two hundred four patients were delabeled (95%) among those fully evaluated. One hundred twelve patients were delabeled by interview and chart review alone (52%), 99 by oral challenge (46%), and 2 by PST and oral challenge (1%). Twenty-nine patients with moderate to severe reactions were challenged and 27 were delabeled. Ten patients could not be delabeled due to mild or delayed reactions to challenge or subsequent treatment, including 2 patients with severe index reactions who had mild challenge reactions and required no rescue medications. No patients required epinephrine during challenge. Five patients were relabeled and then delabeled again as no new reaction had occurred. Conclusion Penicillin allergies can be removed with a pharmacy-driven algorithm that prioritizes direct challenges when appropriate even when the index reaction was moderate to severe. Risks of a reaction are low, and reactions tend to be mild. Given well-documented benefits of delabeling patients for the patient and the institution, more hospitals should consider starting such services. Disclosures All Authors: No reported disclosures

118. Feasibility of a Proactive Amoxicillin Oral Challenge Program for Inpatients with Penicillin Allergy at the Miami VAMC

Background Ninety percent of patients who report penicillin (PCN) allergy are not truly allergic. Penicillin skin testing (PST) followed by oral challenge (OC) with amoxicillin (AMX) can evaluate unconfirmed PCN allergy. PST is taxing and requires trained staff, while OC is an acceptable alternative in patients with low-risk histories, who can safely undergo OC without PST. OC is performed in the outpatient Miami Veterans Affairs Medical Center (MVAMC) setting. Collaboration between Allergy, Antimicrobial Stewardship Program (ASP), and Hospital Medicine identified patients with low-risk histories and offered OC to inpatients. Methods A daily report of MVAMC inpatients with PCN allergy was reviewed for appropriateness of OC (Fig 1). Hospice patients and those medically unstable or unable to consent were excluded. Appropriate consenting patients were challenged with AMX 500mg PO and observed for 60 minutes. If no reaction resulted, the PCN allergy label was removed. Epinephrine and diphenhydramine were available in case of adverse reaction. Those who were not OC candidates were offered outpatient PST (Fig 1). Figure 1. Penicillin allergy history evaluation algorithm Results We evaluated 39 inpatients with PCN allergy from 3/10 - 5/27/21. Median age was 68 years; 94.9% were male (Table 1). The most common recorded reaction was unknown (Table 2). Thirteen (33.3%) did not qualify for OC, 7 (17.9%) refused, 2 (5.1%) were receiving a penicillin-derivative, 1 (2.6%) patient’s primary team refused consult, 2 (5.1%) patients were discharged prior to OC. Fourteen (38%) patients underwent OC with 0 adverse reactions; 0 patients required epinephrine or diphenhydramine. After OC, 5 patients had changes to their antibiotic regimen as a result of a negative OC. Limitations included 5 patients on beta-blockers, and 5 patients unable to consent. Table 1. Demographics of Evaluated Inpatients, N = 39 (%) Note that 1 patient out of the 39, underwent DPC with cefpodoxime 200mg PO instead of amoxicillin for a reported allergy to ceftriaxone. Table 2. Reported Reactions, N = 41 (%) Total N exceeds evaluated patient number as one patient reported multiple reactions to receiving penicillin. Conclusion Removing unnecessary PCN allergy labels using inpatient OC with AMX is safe and effective for those with low-risk allergy histories. Zero patients undergoing OC developed a reaction, suggesting that OC may be safely performed per our algorithm. Our protocol does not require specialized training and is reproducible in settings without an Allergy specialist. In the 3 months prior to this program there were 0 inpatient consults to evaluate PCN. Future plans include forming a multidisciplinary consult service. Disclosures All Authors: No reported disclosures

Persistence of Antibody After a Vi-Tetanus Toxoid Conjugate Vaccine and Effect of Boosting With a Plain Polysaccharide Vaccine on Vi Antibody and Antigen-Specific B Cells

BackgroundSalmonella enterica serovar Typhi is estimated to cause 9 to 13 million cases of typhoid fever annually. Typhoid conjugate vaccines represent a promising prophylactic measure to prevent disease, but there are few data assessing persistence of immunity. The effect of a Vi polysaccharide booster vaccine in individuals previously vaccinated with the Vi-tetanus toxoid typhoid conjugate vaccine has not been assessed previously.MethodsThirty five healthy adult volunteers received a single dose of the Vi conjugate vaccine (Vi-TT) and 37 received a single dose of Vi polysaccharide vaccine (Vi-PS) prior to oral challenge with live S. Typhi bacteria as part of a randomised controlled, phase 2b study. In addition to data previously published showing persistence of Vi IgG and IgA antibodies for 7 months after Vi vaccination, titres were measured at intervals until 13 months post-vaccination. Ten participants who received Vi-TT (both challenged and unchallenged) were re-vaccinated with Vi-PS at an interval of 19-23 months post-prime. Anti-Vi IgG and IgA titres, and Vi-specific antibody secreting cells and memory B cells were measured at seven days and one month post-boost.FindingsVi IgG and IgA antibody titres remained significantly elevated above baseline levels 13 months after priming with Vi-TT, with a 4-fold rise retained in 90% and 88% of recipients (Vi IgG and IgA, respectively). Anti-Vi IgG and IgA antibody titres were found to persist at higher levels in participants who received a single dose of Vi-TT than in those who received Vi-PS. No significant boost in Vi-antibody titre was observed in response to oral challenge with S. Typhi bacteria, one month after vaccination. Following a Vi-PS booster vaccination in those previously vaccinated with Vi-TT, anti-Vi IgG and IgA titres were significantly elevated, with similar titres observed at one month post-boost compared with one month after primary vaccination. The frequency of Vi-specific IgA antibody secreting cells increased significantly 7 days post-boost compared with pre-boost. No memory B cell response was observed following Vi-PS booster vaccination.InterpretationStrong persistence of anti-Vi IgG and IgA following Vi-TT vaccination suggests that the conjugate vaccine may offer durable protection, supporting its use in endemic settings.