Epidemiology of outpatient visits for Lyme disease, 1993-2010

BACKGROUND:  Lyme disease is the most common vector-borne disease in the United States. National surveillance provides valuable information on overall distribution and trends, but does not capture all cases. The objective of this study was to describe the epidemiology of Lyme disease diagnoses as determined by two national ambulatory care surveys.

METHODS:  The National Hospital Ambulatory Medical Care Survey and the National Ambulatory Medical Care Survey capture outpatient, emergency, and physician office visits in the United States. Data with any ICD-9 diagnostic code for Lyme disease (088.81) from 1993-2010 were included in the weighted analysis using chi-square tests to compare clinical characteristics by age, gender, and season.

RESULTS:  A total of 357 observations accounted for an estimated 303,036 ambulatory care visits during the study period, with 63.4% having a primary diagnosis of Lyme disease. Ages ranged from 0 to 88 with a mean of 36.6 years (s.d.=19.9). A significantly higher proportion of females (91.6%) than males (89.1%) visited a physician’s office versus an outpatient or emergency department (p < 0.05). A majority of the sample was from the Northeast region (78.0%) and visited an ambulatory care center during the summer (34.1%). The most frequent secondary diagnosis was disease of the musculoskeletal system (17.9%). The most common symptoms were arthralgia/myalgia (26.8%), neurologic symptoms (16.4%), fatigue/malaise (12.9%), and skin rash (12.6%). Males had a higher proportion on tetracycline medications (34.9%) than females (22.1%; p < 0.05), and persons older than age 40 years had a higher proportion on tetracycline (31.5%) than those ≤ 40 years (21.3%; p < 0.05).

DISCUSSION:  Demographic, seasonal, and clinical characteristics were similar to national surveillance data, but appear to underrepresent the general Lyme disease population.