In an IDWeek 2023 session titled Two Decades of Lyme Disease in the U.S. Veterans Health Administration Detected Via Automated Surveillance Methodology, October 1999–September 2022, Gina Oda, MS, health science specialist, Department of Veterans Affairs, updated trends in Lyme disease transmission and surveillance. She assessed the impact of global warming and presented an algorithm that “offers simple, efficient, standardized surveillance definition based on electronically available data.”

Ms. Oda said Lyme disease is “most common vector-borne disease in the United States,” with 35,000 cases reported annually via traditional surveillance methods. Caused by the bacterium Borrelia burgdorferi, mayonii (less commonly), Lyme disease is transmitted by the blacklegged tick, Ixodes scapularis or Ixodes pacificus.

Signs and symptoms of early infection, Ms. Oda said, are fever, headache, fatigue, and the characteristic skin rash that occurs in 70% to 80% of cases. Late-stage manifestations, she added, are musculoskeletal (arthritis with joint swelling); central nervous system (lymphocytic meningitis, cranial neuritis, radiculoneuropathy, encephalomyopathy); and cardiovascular (high-grade atrioventricular conduction defect).

To understanding current endemicity and appreciate the need for increasingly close monitoring, she said, one must acknowledge the effect of climate change. Changing temperatures, she pointed out, are leading to expanded blacklegged ticks ranges.

To gain a better picture of the scope of Lyme disease, the Veterans Health Administration (VHA) developed and validated a standardized, automated methodology to identify Lyme cases and track trends utilizing VHA electronic health record data. From October 1999 through September 2022, the study examined patients receiving care at all 1,300 VHA inpatient and outpatient healthcare facilities nationwide, collecting data such as state and rurality of residence, birth sex, age, race/ethnicity. To validate the findings, 150 cases were randomly selected for chart review and positive predictive value was calculated.

Criteria for inclusion included an outpatient or inpatient encounter with an ICD-9 088.81 or ICD-10 A69.2x diagnosis code, as well as an outpatient prescription for more than 7 days with an appropriate antimicrobial for Lyme disease filled within 30 days of encounter. Additional inclusion criteria included confirmatory laboratory evidence from either a positive nucleic acid amplification test, an immunoblot test, or positive or equivocal results from a Lyme disease antibody test.

The VHA-developed algorithm, Ms. Oda said, “provides simple, efficient, standardized surveillance definition based on electronically available data.” The tool does not rely on clinician reporting or changing surveillance case definitions, so it may provide more consistent representation of case incidence over time, she said, and it provides a reliable estimate of Lyme incidence, particularly for high incidence states. “The algorithm was most accurate when ICD code plus antimicrobial treatment was coupled with laboratory criteria,” she added.