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Current Trends Lyme Disease -- United States, 1987 and 1988
In 1987 and 1988, CDC surveyed state health departments for reported cases of Lyme disease (LD (Lyme borreliosis)); in 1987, 2368 cases meeting the case definition* of their respective states were reported, and in 1988, 4572 cases were reported. Demographic data were available for 54% of reported cases: 92% were white, 4% Hispanic, 2% black, and 2% Asian; 51% of cases occurred in females. Age-specific incidence rates were highest for children less than 15 years of age and for persons 25-44 years of age (0.2 per 100,000 population). In the Northeast and North Central regions, 64% of LD patients had onset of illness from May through August; in comparison, in the Pacific region, where 33% of patients had onset in these months, more cases occurred from January through May.
In 1987 and 1988, cases were reported from all states; however, in nine states, infection was thought to have been acquired out of state (Figure 1). Indigenous cases now have been reported in all states except Alaska, Arizona, Hawaii, Montana, Nebraska, New Mexico, and Wyoming. (Missouri and Nevada did not report indigenous cases in 1987 or 1988 but had done so previously.) In 1987 and 1988, 94% of U.S. cases were reported from nine states: New York, New Jersey, Wisconsin, Connecticut, Pennsylvania, Rhode Island, California, Massachusetts, and Minnesota; the six states in the upper northeast accounted for 80% of all cases. In 1988, New York state reported 56% of all cases, and two suburban counties of New York City (Westchester and Suffolk) reported 44% of U.S. cases. LD remains rare in the Mountain region, where, in 1987 and 1988, five cases were reported, and nine cases have been reported since 1980.
Estimates of regional incidence (per 100,000 persons) varied approximately 100-fold: 6.1 in the Mid-Atlantic region, 3.7 in New England, 0.7 in the North Central states, 0.6 in the Pacific states than 0.1 in the Mountain region (2). Reported by: State and local health departments. Div of Vector-Borne Infectious Diseases, Center for Infectious Diseases, CDC.
National surveillance for LD relies on states for reports. Since 1982, when national surveillance began, state surveillance systems for LD have changed considerably. LD has been made a reportable disease in 31 states and the District of Columbia, and surveillance for LD has intensified, especially in areas where the disease is endemic.
Since 1982, 13,825 cases of LD have been reported. From 1982 through 1987, the number of cases increased nearly fivefold from 492 to 2368; in 1988, reported cases doubled (4572 cases) (Figure 2). LD is the most commonly reported vectorborne disease in the United States (Figure 3). From 1983 through 1987, LD accounted for 50% of the vectorborne infections reported to CDC. Tickborne diseases (e.g., LD, Rocky Mountain spotted fever (RMSF)) accounted for 95% of these infections; fleaborne typhus and plague and mosquitoborne arboviral infections accounted for the remaining 5%.
The increased incidence of reported LD probably is due to improved awareness and recognition of the disease, as well as to an actual increase in incidence and geographic spread. Other factors may also contribute to the increase. For example, because the clinical and laboratory diagnosis of LD may be imprecise (3), other conditions possibly may be misdiagnosed and reported as LD. In addition to differences in clinical interpretation of erythema migrans (EM), misdiagnosis may also result from the lack of standardization of serologic testing and from cross-reactivity with Treponema and with other Borrelia (3). In areas with endemic LD, persons with illnesses other than LD--but who previously have been infected with B. burgdorferi (the causative agent for LD)--also may be misdiagnosed (4). Conversely, several factors may be responsible for failure of a case of LD to be diagnosed and/or to meet the case definition. These include early treatment of symptoms resulting in abrogation of the specific antibody response (3), the low sensitivity of serologic tests in early LD (3), and the failure of approximately 25% of LD patients to manifest EM (4,5). The extent of underreporting of LD is unknown.
Until more sensitive and specific laboratory diagnostic tests become available, diagnosis of LD relies predominantly on clinical features. Serologic testing may be of greatest diagnostic utility in patients who have symptoms compatible with late-stage LD. The validity of serologic test results depends largely on the experience of the diagnostic laboratory and its quality-control procedures. No published data exist on the diagnostic utility of antigen-detection assays in the laboratory diagnosis of LD. A comparative study of licensed LD diagnostic kits is planned by the Association of State and Public Health Laboratory Directors.
State- and community-based epidemiologic studies have documented an increase in human cases and an expansion of affected areas (5-8). Entomologic surveys have detected local increases of Ixodes dammini, the principal tick vector in northeastern and central states, and its spread to new areas (7-10). However, because the risk for acquiring LD varies widely by locality, the disease appears to be of public health consequence only in certain regions--specifically, coastal counties on both seaboards and in certain counties in the upper Midwest. In the southeastern, southwestern, and Mountain states, RMSF remains the leading vectorborne disease: from 1983 through 1987, 3160 RMSF and 658 LD cases were reported from the Southeast and Southwest, and 37 RMSF and seven LD cases were reported from the Mountain states.
Data concerning risk factors for acquiring LD are limited. In suburban areas where LD is endemic, infection may be acquired principally around patients' residences (11,12), and risk of exposure may be continuous during the transmission season. Under these circumstances, certain personal protection measures (e.g., the daily application of repellents) may not be practical. Further efforts are needed to evaluate the effectiveness of environmental modifications and focal application of acaricides (chemicals effective against ticks) for the control of vector ticks in these circumstances. Where LD is transmitted sporadically through occasional or brief exposures during recreation or work, personal protection measures are most appropriate for prevention.
Measures recommended to reduce exposure to ticks include avoiding areas endemic for LD; using repellents; wearing long-sleeved shirts and long pants, and tucking pants into the top of socks; wearing light-colored clothing; and inspecting clothing and skin frequently for ticks. Animal studies suggest that I. dammini may not efficiently transmit infection until after 48 hours of attachment and that prompt removal of attached ticks may limit transmission (13). However, it is unknown how long a tick must attach to human hosts before infection occurs.
N,N-diethyl-m-toluamide (DEET) is effective in repelling I. dammini and other vector ticks. In view of the possible risk for toxicity (14), the use of DEET-containing repellents solely to prevent LD may be inappropriate in areas without endemic LD. Permethrin (0.5%) sprayed onto clothing also is effective in reducing the numbers of adherent ticks, including I. dammini and others (15,16). However, permethrin aerosols are available only in certain states that have obtained Environmental Protection Agency approval for their distribution.
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4. Steere AC. Lyme disease. N Engl J Med 1989;321:586-96. 5. Cartter ML, Mshar P, Hadler JL. The epidemiology of Lyme disease in Connecticut. Conn Med 1989;53:320-3.
6. Steere AC, Taylor E, Wilson ML, Levine JF, Spielman A. Longitudinal assessment of the clinical and epidemiological features of Lyme disease in a defined population. J Infect Dis 1986;154:295-300.
7. Lastavica CC, Wilson ML, Berardi VP, Spielman A, Deblinger RD. Rapid emergence of a focal epidemic of Lyme disease in coastal Massachusetts. N Engl J Med 1989;320:133-7.
8. Hanrahan JP, Benach JL, Coleman JL, et al. Incidence and cumulative frequency of endemic Lyme disease in a community. J Infect Dis 1984;150:489-96.
9. Spielman A, Wilson ML, Levine JF, Piesman J. Ecology of Ixodes dammini-borne human babesiosis and Lyme disease. Annu Rev Entomol 1985;30:439-60. 10. Davis JP, Schell WL, Amundson TE, et al. Lyme disease in Wisconsin; epidemiologic, clinical, serologic and entomologic findings. Yale J Biol Med 1984;57:685-96. 11. Falco RC, Fish D. A survey of tick bites acquired in a Lyme-disease endemic area in southern New York State. Ann N Y Acad Sci 1988;539:456-7. 12. Falco RC, Fish D. Prevalence of Ixodes dammini near the homes of Lyme disease patients in Westchester County, New York. Am J Epidemiol 1988;127:826-30. 13. Piesman J, Mather TN, Sinsky RJ, Spielman A. Duration of tick attachment and Borrelia burgdorferi transmission. J Clin Microbiol 1987;25:557-8. 14. CDC. Seizures temporally associated with use of DEET insect repellent--New York and Connecticut. MMWR 1989;38:678-80. 15. Schreck CE, Snoddy EL, Spielman A. Pressurized sprays of permethrin or DEET on military clothing for personal protection against Ixodes dammini (Acari: Ixodidae). J Med Entomol 1986;23:396-9. 16. Mount GA, Snoddy EL. Pressurized sprays of permethrin and DEET on clothing for personal protection against the Lone Star tick and the American dog tick (Acari: Ixodidae). J Econ Entomol 1983;76:529-31. *The surveillance case definition for LD varies among states and between states and CDC. Some states use the CDC case definition adopted in 1988, i.e., physician-diagnosed erythema migrans (EM) in a person who acquired infection in a county with endemic LD or, for persons who acquired infection in a county without endemic LD, laboratory evidence of infection in addition to the presence of EM. Other states (e.g., New York, Wisconsin, Connecticut) use a previous, more inclusive, CDC case definition for LD, which counts as cases persons with appropriate systemic manifestations and laboratory evidence of infection (1). Differences in the case definitions used by states must be considered when state and regional incidences are compared.
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