Lyme Disease, 2013

Lyme disease is a bacterial infection caused by Borrelia burgdorferi, a spirochete transmitted to humans by bites from I. scapularis (the blacklegged tick or deer tick) in Minnesota. In Minnesota, the same tick vector also transmits the agents of babesiosis, Anaplasmosis, one form of human ehrlichiosis, and a strain of Powassan virus.

In 2013, 1,431 confirmed Lyme disease cases (26.6 cases per 100,000 population) were reported (Figure 1). In addition, 909 probable cases (physician-diagnosed cases that did not meet clinical evidence criteria for a confirmed case but that had laboratory evidence of infection) were reported. The 1,431 confirmed cases represent a 9.6% increase from the previous record of 1,293 confirmed cases reported in 2010. Despite some small yearly fluctuations, the number of reported cases of Lyme disease has been increasing, as evidenced by the median number of cases from 2005 through 2012 (median, 1,065; range, 912 to 1,431) compared to the median from 1996 to 2004 (median, 463; range, 252 to1,023).

Nine hundred seventeen (64%) confirmed cases in 2013 were male. The median age of cases was 42 years (range, 1 to 88 years). Physician-diagnosed erythema migrans (EM) was present in 1,083 (76%) cases. Three hundred eighty-one (27%) cases had one or more late manifestations of Lyme disease (including 238 with a history of objective joint swelling, 117 with cranial neuritis, 15 with lymphocytic meningitis, 13 with acute onset of 2nd or 3rd degree atrioventricular conduction defects, 9 with radiculoneuropathy, and 1 with encephalomyelitis) and confirmation by Western immunoblot (positive IgM ≤30 days post-onset or positive IgG). Of the 1,338 cases with known onset dates, onset of illnesses peaked from June through August, with 40% of EM cases experiencing symptom onset in July. This timing corresponds with peak activity of nymphal I. scapularis ticks in mid-May through mid-July. The majority of cases in 2013 either resided in or traveled to endemic counties in north-central, east-central, or southeast Minnesota, or Wisconsin.

• For up to date information see: Lyme disease
• Full issue>> Annual Summary of Communicable Diseases Reported to the Minnesota Department of Health, 2013