Lyme Disease Surveillance in New York State: an Assessment of Case Underreporting

Despite the mandatory nature of Lyme disease (LD) reporting in New York State (NYS), it is believed that only a fraction of the LD cases diagnosed annually are reported to public health authorities. Lack of complete LD case reporting generally stems from (i) lack of report of provider-diagnosed cases where supportive laboratory testing is not ordered or results are negative (i.e. provider underreporting) and (ii) incomplete case information (clinical laboratory reporting only with no accompanying clinical information) such that cases are considered 'suspect' and not included in national and statewide case counts (i.e. case misclassification). In an attempt to better understand LD underreporting in NYS, a two-part study was conducted in 2011 using surveillance data from three counties. Case misclassification was assessed by obtaining medical records on suspect cases and reclassifying according to the surveillance case definition. To assess provider underreporting, lists of patients for whom ICD-9-CM code 088.81 (LD) had been used were reported to NYS Department of Health (NYSDOH). These lists were matched to the NYSDOH case reporting system, and medical records were requested on patients not previously reported; cases were then classified according to the case definition. When including both provider underreporting and case misclassification, approximately 20% (range 18.4-24.6%) more LD cases were identified in the three-county study area than were originally reported through standard surveillance. The additional cases represent a minimum percentage of unreported cases; the true percentage of unreported cases is likely higher. Unreported cases were more likely to have a history of erythema migrans (EM) rash and were more likely to be young paediatric cases. Results of the study support the assertion that LD cases are underreported in NYS. Initiatives to increase reporting should highlight the importance of reporting clinically diagnosed EM and be targeted to those providers most likely to diagnose LD, specifically providers treating paediatric patients.