ATLANTA Could Lyme disease be on the rise?
According to a recent CDC report, Lyme disease cases increased
from 1991-1999. Although the number of cases decreased from 16,801 reported in
1998 to 16,273 reported in 1999 (3% decrease), the number of cases was still
higher than that reported during the early 1990s. Most cases continue to occur
in the Northeast, mid-Atlantic and North Central states.
In 1999, 713 (22.7%) out of 3,143 U.S. counties reported at least
1 case and 90% of the cases were from 109 (15.3%) reporting counties. Incidence
exceeded 100 cases per 100,000 population in 24 counties in Connecticut,
Maryland, Massachusetts, Minnesota, New Jersey, New York, Pennsylvania, Rhode
Island and Wisconsin. The highest county-specific incidence (950.7) occurred in
Nantucket County, Mass.
Most patients were younger than 15 years and between 45-59 years.
This could be the result of many different scenarios, one being that they
experienced greater exposure than other groups to infected ticks. Others
included less use of personal protective measures, differential use of health
care services or reporting bias. Also, the large number of reported cases
during June and July reflects the seasonal peak of tick activity in endemic
With these findings come at least three limitations. First,
distribution of reported cases could be distorted by reporting bias. The second
limitation could be that Lyme disease is underreported in areas where it is
endemic and overreported where it is not endemic. Third, the Lyme disease case
definition also is limited in sensitivity and specificity. Because all cases of
Lyme disease do not present the same symptoms, other conditions may be
misdiagnosed. Laboratory testing may also be inaccurate.
Avoiding tick-infested areas, using repellents, promptly removing
ticks from clothing or skin and reducing tick populations can prevent Lyme
disease. If the disease is caught early and treated, morbidity can be reduced.
A vaccine (LYMErix, GlaxoSmithKline) for individuals aged 15-70 years, approved
by the FDA in 1998, is 76% effective in preventing Lyme disease after 3 doses.
New methods of reducing tick vectors are also being developed including baited
devices that passively apply acaricides to deer and rodents.
The CDC is collaborating with health departments and
organizations to increase prevention efforts. Throughout the year, community
projects are being initiated to reduce incidence to 9.7 per 100,000 population
by 2010 in states where Lyme disease is endemic.
For more information:
- CDC. Lyme disease United States, 1999.