1313. Clinical significance of Rickettsia rickettsii antibody testing among children in Eastern Long Island, New York

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Abstract Background Rocky Mountain spotted fever (RMSF) is a tickborne illness caused by Rickettsia rickettsii (Rr). Diagnosis is challenging due to non-specific symptoms and reliance on convalescent antibodies (Ab) for definitive diagnosis. Early doxycycline administration reduces poor outcomes but is sometimes prescribed without clear exposure or suggestive symptoms. Confusion also arises from positive Ab testing in patients lacking RMSF symptoms. Our study aims to describe Rr Ab results and clinical impact in a low incidence region. Specific objectives were to describe signs and symptoms of children tested for RMSF, false-positive Ab rates, and unnecessary antibiotic administration. Methods Retrospective chart review of patients ≤ 21 years old tested for Rr Ab within the Stony Brook Medicine system from 2010-2020. Patients were identified by ICD-9/-10 RMSF diagnosis code and/or Ab test results. Charts without clinical notes were excluded. Data collected included demographics, symptoms, laboratory results, treatments, and outcomes. Patients were classified as RMSF confirmed, probable, suspected, unlikely, or negative based on symptoms and Ab results, per CDC definitions (Table). Results recorded in Qualtrics. Descriptive statistics were calculated. ‘Unlikely RMSF’ cases were considered false positive Ab and ‘proven’ or ‘probable’ cases were considered true positive Ab. Case definitions based on CDC Rocky Mountain spotted fever (RMSF) case surveillance definition Abbreviation: Rr - Rickettsia rickettsii Results 172 charts were included. Average age was 14 years. 56% were male. Of RMSF classic triad symptoms, 52% had fever, 41% rash, and 44% headache. Of RMSF case categories, 2 (1.2%) were confirmed, 3 (1.7%) probable, 10 (5.8%) suspected, 14 (8.1%) unlikely, and 143 (83%) negative. Both confirmed cases had fever, rash and headache. False positive and true positive Rr Ab rates were 8.9% (n=5) and 2.9% (n=5), respectively. 5 patients with false positive Ab received doxycycline within 14 days of Ab collection date. Conclusion Among children in a low-incidence region, Rr Ab were frequently obtained without signs of infection, including half without fever. The cause of false positive Rr Ab in patients lacking RMSF symptoms is unknown, but may be due to non-severe infection or cross-reactivity with other Rickettsia. Focused testing on those with suggestive symptoms may avoid unnecessary treatment and anxiety. Disclosures All Authors: No reported disclosures.