(A-055) A Feasibility Study of Identifying Patients with Chlamydial Infections in a US Claims-Based Database

Background: Identifying patients with chlamydial infections using claims data can be challenging as laboratory test results are often unavailable. Prior studies found that using diagnosis codes only identified a small portion of chlamydia cases, while the feasibility of combining diagnosis codes with claims for laboratory tests and treatment to identify patients with chlamydia has not been explored in a claims database.

Objectives: To identify patients with chlamydial infections in the US Optum’s de-identified Clinformatics® Data Mart Database (CDM) and to describe patient characteristics, treatment patterns, and use of laboratory tests.

Methods: Using Optum® CDM, a descriptive cohort study was conducted in patients aged 14-44 years with ≥1 International Classification of Diseases, Tenth Revision, Clinical Modification (ICD-10-CM) diagnosis code of chlamydial infections (A55, A56, A74, J16.0, A71) between January 1, 2016 and October 31, 2023. Patients with chlamydia were identified by a combination of ≥1 inpatient ICD-10-CM code, ≥2 outpatient ICD-10-CM codes (1-30 days apart), or only 1 outpatient ICD-10-CM code and ≥1 laboratory test claim for chlamydia within 30 days before or after the outpatient code. We excluded patients without 30-day continuous enrollment before or after the index date (i.e., first ICD-10-CM code). Patient characteristics and use of antibiotics (azithromycin or doxycycline) and laboratory tests were described. In sensitivity analyses, we identified patients using ICD-10-CM codes only or combined with treatment.

Results: We identified 85,126 patients (mean age: 26 ± 6.6 years, 69.8% female); 47.1% were white and 19.2% were black patients. Females were younger than males (mean age: 25 vs 28 years). Between 2016-2020, azithromycin was the most common treatment (43.3%) followed by doxycycline (7.5%). Since 2021 when CDC changed chlamydia treatment guidelines, the use of azithromycin declined (32.2% to 14.5%) while doxycycline increased (18.1% to 32.5%). Most patients were treated within 7 days on and after the index date. However, 43.0% of patients had no documented treatment for chlamydia. About 98.6% of patients had ≥1 claim for laboratory tests for chlamydia with no sex difference. Sensitivity analyses showed consistent results, except that compared to the main results, use of laboratory tests decreased to 90% and females were more likely to receive tests than males.

Conclusions: The large proportion of untreated patients suggested that many individuals may have been misclassified as chlamydia cases. This emphasizes the challenges of identifying chlamydia cases without laboratory test results using claims data and suggests adding antibiotics use as an additional criterion.