Lyme Disease, 2016
Lyme disease is caused by B. burgdorferi, a spirochete transmitted to humans by bites from Ixodes scapularis (the blacklegged tick or deer tick). Recently, a new species of bacteria, B. mayonii, has also been identified as a cause of human disease. 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 2016, 1,305 confirmed Lyme disease cases (23.78 cases per 100,000 population) were reported. In addition, 821 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. Despite some yearly fluctuations, the number of reported cases of Lyme disease has been increasing, as evidenced by the median number of cases from 2006 through 2016 (median, 1,176; range, 896 to 1,431) compared to the median from 1996 to 2005 (median, 464; range, 252 to 1,023) (Figure 1).
Eight hundred one (62%) confirmed cases in 2016 were male. The median age of cases was 49 years (range, 1 to 100 years). Physician-diagnosed erythema migrans (EM) was present in 973 (75%) cases. Four hundred one (31%) cases had one or more late manifestations of Lyme disease (including 262 with a history of objective joint swelling, 115 with cranial neuritis including Bell’s Palsy, 21 with acute onset of 2nd or 3rd degree atrioventricular conduction defects, 9 with lymphocytic meningitis, and 4 with radiculoneuropathy) and confirmation by Western immunoblot (positive IgM ≤30 days post-onset or positive IgG). Of the 1,200 cases with known onset dates, onset of symptoms peaked from June through August, with 61% of EM cases experiencing symptom onset in June or July. This timing corresponds with peak activity of nymphal I. scapularis ticks in mid- May through mid-July. The majority of cases 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, 2016