Incidence of Clinician-Diagnosed Lyme Disease, United States, 2005-2010

Abstract

National surveillance provides important information about Lyme disease (LD) but is subject to underreporting and variations in practice. Information is limited about the national epidemiology of LD from other sources. Retrospective analysis of a nationwide health insurance claims database identified patients from 2005-2010 with clinician-diagnosed LD using International Classification of Diseases, Ninth Revision, Clinical Modification, codes and antimicrobial drug prescriptions. Of 103,647,966 person-years, 985 inpatient admissions and 44,445 outpatient LD diagnoses were identified. Epidemiologic patterns were similar to US surveillance data overall. Outpatient incidence was highest among boys 5-9 years of age and persons of both sexes 60-64 years of age. On the basis of extrapolation to the US population and application of correction factors for coding, we estimate that annual incidence is 106.6 cases/100,000 persons and that ≈329,000 (95% credible interval 296,000-376,000) LD cases occur annually. LD is a major US public health problem that causes substantial use of health care resources.

Keywords: Borrelia burgdorferi; EIP; Emerging Infections Program; Ixodes; Lyme disease; United States; surveillance; vector-borne infections; zoonoses.

Figure 1

Study population and number of patients with clinician-diagnosed Lyme disease in the MarketScan database, United States, 2005–2010. *Persons not enrolled for the full 12 months of any year and who did not have prescription data were removed from both the numerator and denominator for rate calculations. Therefore, removal of these persons did not substantially affect rate calculations and the final estimated number of cases. †One repeat inpatient was excluded (admitted in a subsequent year but <365 days after initial admission). No repeat admissions occurred >365 days after initial admission. ‡A total of 2,945 repeat outpatients (seen in a subsequent year but <365 days after previous year’s visit) were excluded (Technical Appendix). ICD–9, International Classification of Diseases, Ninth Revision.

Figure 2

Trends of annual incidence of Lyme disease in MarketScan compared with trends in incidence from US surveillance, 2005–2010. Incidence is per 100,000 persons. Trends in interannual incidence fluctuation did not differ significantly between MarketScan and US surveillance (χ² test, p = 0.81). *Cases reported through the National Notifiable Diseases Surveillance System. During 2005–2007, incidence was calculated as the number of confirmed cases/100,000 persons; during 2008–2010, incidence was calculated as the number of confirmed and probable cases/100,000 persons. US 2010 Census population estimates were used as the denominator for surveillance data incidence calculations.

Figure 3

Seasonal distribution of inpatient and outpatient clinician-diagnosed Lyme disease in MarketScan compared with US surveillance cases, 2005–2010. *Because information about hospitalization is not consistently captured by surveillance, US surveillance data include both inpatients and outpatients. †Date of symptom onset for surveillance cases; date of admission or first outpatient visit for MarketScan events.

Figure 4

Comparison of trends in the age and sex distribution of persons with Lyme disease in MarketScan with US surveillance, 2005–2010. Incidence is per 100,000 persons. Age distribution of persons with Lyme disease in MarketScan did not differ from those reported through US surveillance (male patients: χ² test, p = 0.57; female patients: χ² test, p = 0.43). *US 2010 Census population estimates were used as the denominator for surveillance incidence calculations.

Figure 5

Comparison of states and district with highest incidence per 100,000 persons of Lyme disease in MarketScan (gray fill) and US surveillance (black dots), 2005–2010. Each dot is placed randomly within the county of residence for each confirmed Lyme disease case reported through surveillance during 2010.