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Lyme Disease -- United States, 1994

For surveillance purposes, Lyme disease (LD) is defined as the presence of an erythema migrans rash greater than or equal to 5 cm in diameter or laboratory confirmation of infection with Borrelia burgdorferi and at least one objective sign of musculoskeletal, neurologic, or cardiovascular disease (1). In 1982, CDC initiated surveillance for LD, and in 1990, the Council of State and Territorial Epidemiologists adopted a resolution that designated LD a nationally notifiable disease. This report summarizes surveillance data for LD in the United States during 1994.

In 1994, 13,083 cases of LD were reported to CDC by 44 state health departments, 4826 (58%) more than the 8257 cases reported in 1993 Figure_1. As in previous years, most cases were reported from the northeastern and north-central regions Figure_2. The overall incidence of reported LD was 5.2 per 100,000 population. Eight states reported incidences of more than 5.2 per 100,000 (Connecticut, 62.2; Rhode Island, 47.2; New York, 29.2; New Jersey, 19.6; Delaware, 15.5; Pennsylvania, 11.9; Wisconsin, 8.4; and Maryland, 8.3); these states accounted for 11,476 (88%) of nationally reported cases. Six states (Alaska, Arizona, Hawaii, Mississippi, Montana, and North Dakota) reported no cases. Reported incidences were greater than or equal to 100 per 100,000 in 15 counties in Connecticut, Maryland, Massachusetts, New Jersey, New York, Pennsylvania, and Wisconsin; the incidence was highest in Nantucket County, Massachusetts (1197.6).

Six northeastern states accounted for 95% of the increase in reported cases for 1994: Maryland, New Jersey, New York, Rhode Island, Connecticut, and Pennsylvania. Reported cases increased by 218 cases (121%) in Maryland, 747 cases (95%) in New Jersey, 2382 cases (85%) in New York, 199 cases (73%) in Rhode Island, 680 cases (50%) in Connecticut, and 353 cases (33%) in Pennsylvania. Reported cases remained stable in the states with endemic disease in the north-central region (Minnesota and Wisconsin) and decreased in California (36%).

Males and females were nearly equally affected in all age groups except those aged 10-19 years (males: 55%) and those aged 30-39 years (females: 56%). Reported by: State health departments. Bacterial Zoonoses Br, Div of Vector-Borne Infectious Diseases, National Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: LD is the most commonly reported vectorborne infectious disease in the United States. Infection with B. burgdorferi results from exposure to nymphal and adult forms of tick vectors of the genus Ixodes: I. scapularis (black-legged tick) in the northeastern and upper north-central United States, and I. pacificus (western black-legged tick) in the Pacific coastal states.

Risk for exposure to B. burgdorferi is strongly associated with the prevalence of tick vectors and the proportion of those ticks that carry B. burgdorferi. The risk for exposure may be highly focal (2) and can differ substantially between adjacent states, counties, communities, and areas on the same residential property (3,4). In northeastern states with endemic disease, the infection rate of nymphal I. scapularis ticks with B. burgdorferi is commonly 20%-35%, and even modest changes in tick numbers can substantially affect the risk for exposure to infected vectors (5). In one area of Connecticut where approximately 15% of I. scapularis are infected with B. burgdorferi, changes in the annual incidence of LD have paralleled changes in I. scapularis densities (M. Cartter, Connecticut Department of Health and Addiction Services, K. Stafford, Connecticut Agricultural Experimental Station, personal communication, 1995). In 1994, tick surveillance in the Northeast indicated increases over previous years in vector tick density. For example, in one site in Westchester County, New York, population density of I. scapularis nymphs increased 400% from 0.4 nymphs per square meter in 1993 to 1.6 nymphs per square meter in 1994 (T. Daniels, Fordham University, R. Falco, Westchester County Department of Health, personal communication, 1995), and in Rhode Island, nymphal I. scapularis density measured at sites throughout the state increased 158% from 1993 to 1994 (T. Mather, University of Rhode Island, personal communication, 1995).

Ascertainment of LD cases based only on passive surveillance may result in underreporting of cases (6,7). Because of this and in accordance with recommendations for control of emerging diseases (8), some states in which LD is endemic have expanded surveillance efforts. In 1994, the New York State Department of Health augmented surveillance with additional staff, intensified active case detection, and validated some cases reported in the previous year; these efforts probably accounted for some of the increase in reported cases for New York in 1994 (D. White, New York State Department of Health, personal communication, 1995). Active surveillance, with support from CDC, is conducted by health departments in Connecticut, Michigan, Minnesota, New Jersey, New York, Oregon, Rhode Island, and West Virginia.

The risk for infection among persons residing in or visiting areas where LD is endemic can be reduced through avoidance of known tick habitats; other preventive measures include wearing long pants and long-sleeved shirts, tucking pants into socks, applying tick repellents containing N,N-diethyl-m-toluamide ("DEET") to clothing and/or exposed skin according to manufacturer's instructions, checking thoroughly and regularly for ticks, and promptly removing any attached ticks. Acaracides containing permethrin kill ticks on contact and can provide further protection when applied to clothing, but are not approved for use on skin.

Additional information about LD is available from state and local health departments, from CDC's Voice Information System, telephone (404) 332-4555; from CDC's Bacterial Zoonoses Branch, Division of Vector-Borne Infectious Diseases, National Center for Infectious Diseases, telephone (970) 221-6453; and from the Office of Communications, National Institute of Allergy and Infectious Diseases, National Institutes of Health, telephone (301) 496-5717.


  1. CDC. Case definitions for public health surveillance. MMWR 1990;39(no. RR-13):19-21.

  2. Piesman J, Gray JS. Lyme disease/Lyme borreliosis. In: Sonenshine DE, Mather TN, eds. Ecological dynamics of tick-borne zoonoses. New York: Oxford University Press, 1994:327-50.

  3. Maupin GO, Fish D, Zultowsky J, Campos EG, Piesman J. Landscape ecology of Lyme disease in a residential area of Westchester County, New York. Am J Epidemiol 1991;133:1105-13.

  4. Spielman A, Wilson ML, Levine JF, Piesman J. Ecology of Ixodes dammini-borne human babesiosis and Lyme disease. Ann Rev Entomol 1985;30:439-60.

  5. Mather TN. The dynamics of spirochete transmission between ticks and vertebrates. In: Ginsberg HS, ed. Ecology and environmental management of Lyme disease. New Brunswick, New Jersey: Rutgers University Press, 1993:43-60.

  6. Ley CT, Davila IH, Mayer NM, Murray RA, Rutherford GW, Reingold AL. Lyme disease in northwestern coastal California. Western J Med 1994;160:534-9.

  7. Jung PI, Nahas JN, Strickland GT, McCarter R, Israel E. Maryland physicians' survey on Lyme disease. Maryland Medical Journal 1994;43:447-50.

  8. CDC. Addressing emerging infectious disease threats: a prevention strategy for the United States. Atlanta, Georgia: U.S. Department of Health and Human Services, Public Health Service, 1994.


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