Lyme Disease --- United States, 2003--2005

Lyme disease is caused by the spirochete Borrelia burgdorferi and is transmitted to humans by the bite of infected blacklegged ticks (Ixodes spp.). Early manifestations of infection include fever, headache, fatigue, and a characteristic skin rash called erythema migrans. Left untreated, late manifestations involving the joints, heart, and nervous system can occur. A Healthy People 2010 objective (14-8) is to reduce the annual incidence of Lyme disease to 9.7 new cases per 100,000 population in 10 reference states where the disease is endemic (Connecticut, Delaware, Maryland, Massachusetts, Minnesota, New Jersey, New York, Pennsylvania, Rhode Island, and Wisconsin) (1). This report summarizes surveillance data for 64,382 Lyme disease cases reported to CDC during 2003--2005, of which 59,770 cases (93%) were reported from the 10 reference states. The average annual rate in these 10 reference states for the 3-year period (29.2 cases per 100,000 population) was approximately three times the Healthy People 2010 target. Persons living in Lyme disease--endemic areas can take steps to reduce their risk for infection, including daily self-examination for ticks, selective use of acaricides and tick repellents, use of landscaping practices that reduce tick populations in yards and play areas, and avoidance of tick-infested areas.

For surveillance purposes, a reportable case of Lyme disease is defined as 1) physician-diagnosed erythema migrans >5 cm in diameter or 2) at least one objective late manifestation (i.e., musculoskeletal, cardiovascular, or neurologic) with laboratory evidence of infection with B. burgdorferi in a person with possible exposure to infected ticks (2). This surveillance case definition was developed for national reporting of Lyme disease; it is not intended to be used in clinical diagnosis (2). For this report, annual Lyme disease rates in 2003, 2004, and 2005 were calculated by county, state, and age group, using reported cases and midyear U.S. Census population estimates for each year. To limit reporting bias, analysis of symptom data was restricted to six of the 10 reference states where >90% of records included symptom information.

During 2003--2005, CDC received reports of 64,382 Lyme disease cases from 46 states and the District of Columbia; 93% of cases occurred among residents of the 10 Healthy People 2010 reference states (Table, Figure 1). The average annual rate in these 10 reference states for the 3-year period was 29.2 cases per 100,000 population: 29.1 in 2003, 26.8 in 2004, and 31.6 in 2005. During 2003--2005, three counties had annual rates above 300 cases per 100,000 population in all 3 years: Columbia and Dutchess counties in New York and Dukes County in Massachusetts. Information on patient age and sex was available for 62,206 (97%) of reported cases. Median age of patients was 41 years, and patient ages followed a bimodal distribution (Figure 2). Males accounted for 54% of reported cases overall and 61% of cases among children aged 5--14 years. Records for 31,961 (50%) cases specified the race of the patient; 97% were identified as white, 2% as black, and <1% as Asian/Pacific Islander or American Indian/Alaska Native.

Reported date of illness onset was available for 49,157 (76%) case reports during 2003--2005. Patients were most likely to have illness onset in May (7%), June (25%), July (29%), or August (13%); fewer than 8% were reported with illness onset during the period December--March. Records for 32,095 (50%) patients met the criteria for evaluation of symptoms. A history of erythema migrans was reported for 70% of these patients, arthritis for 30%, facial palsy for 8%, radiculopathy for 3%, meningitis or encephalitis for 2%, and heart block for <1%.

Reported by: State and District of Columbia health departments. RM Bacon, MS, KJ Kugeler, MPH, KS Griffith, MD, PS Mead, MD, Div of Vector-Borne Infectious Diseases, National Center for Zoonotic, Vector-Borne, and Enteric Diseases, CDC.

Editorial Note:

With approximately 20,000 new cases reported each year, Lyme disease is the most common vector-borne disease in the United States. Cases occur most commonly in northeastern, mid-Atlantic, and north-central states and among persons aged 5--14 years and 45--54 years. Cases peak during summer months, reflecting transmission by nymphal vector ticks during May and June.

Since Lyme disease became nationally notifiable in 1991, the annual number of reported cases has more than doubled. This increase likely is the result of several factors, including a true increase in disease incidence and enhanced case detection resulting from implementation of laboratory-based surveillance in several states. The growing number of case reports and the labor required for confirmation of laboratory-reported cases has placed considerable burden on local and state health departments in areas where Lyme disease is endemic. To address this surveillance burden and create more sustainable Lyme disease surveillance systems, some states have modified components of their systems, leading to acute reductions in reported cases (3). However, no evidence exists to suggest a true decrease in Lyme disease incidence in these states.

The findings in this report are subject to at least three limitations. First, Lyme disease surveillance is complicated by both underreporting and overdiagnosis of cases (4,5). Second, differences in patient demographics (e.g., age and sex) among states with above-average and below-average incidence suggest variation in diagnostic and reporting practices among states (6). Finally, clinical information on symptoms is not verified independently and often is incomplete.

The Healthy People 2010 target (1) was derived from a baseline of 17.4 cases per 100,000 population reported to CDC during 1992--1996 and was established in anticipation of widespread use of a Lyme disease vaccine, licensed in 1999. However, the vaccine was withdrawn from the market in 2002, reportedly because of poor sales (7). Although no Lyme disease vaccine is available, persons can lower their risk for the disease and other tickborne illnesses by avoiding tick-infested areas when possible, using insect repellents containing DEET (N,N-diethyl-m-toluamide), and performing daily self-examination for ticks (7). In North America, removing ticks within 24 hours of attachment reduces the likelihood of B. burgdorferi transmission (8). Tick populations around homes and in recreational areas can be reduced 50%--90% through simple landscaping practices such as removing brush and leaf litter or creating a buffer zone of wood chips or gravel between forest and lawn or recreational areas. For persons who are infected, prompt diagnosis and treatment are important to prevent serious illness and long-term complications (9,10). Detailed information regarding Lyme disease prevention is available at http://www.cdc.gov/ncidod/dvbid/lyme.

References

1. US Department of Health and Human Services. Healthy people 2010 (conference ed, in 2 vols). Washington, DC: US Department of Health and Human Services; 2000. Available at http://www.health.gov/healthypeople.
2. CDC. Case definitions for infectious conditions under public health surveillance. MMWR 1997;46(No. RR-10).
3. Lyme disease---Connecticut, 2005. Connecticut Epidemiologist 2006;26:13--4. Available at http://www.dph.state.ct.us/bch/infectiousdise/pdf/vol26no4_fnlclr.pdf.
4. Naleway AL, Belongia EA, Kazmierczak JJ, Greenlee RT, Davis JP. Lyme disease incidence in Wisconsin: a comparison of state-reported rates and rates from a population-based cohort. Am J Epidemiol 2002;155:1120--7.
5. Steere AC, Taylor E, McHugh GL, Logigian EL. The overdiagnosis of Lyme disease. JAMA 1993;269:1812--6.
6. CDC. Lyme disease---United States, 2001--2002. MMWR 2004;53:365--9.
7. Hayes EB, Piesman J. How can we prevent Lyme disease? N Engl J Med 2003;348:2424--30.
8. Piesman J, Dolan MC. Protection against Lyme disease spirochete transmission provided by prompt removal of nymphal Ixodes scapularis (Acari: Ixodidae). J Med Entomol 2002;39:509--12.
9. Wormser GP, Dattwyler RJ, Shapiro ED, et al. The clinical assessment, treatment, and prevention of Lyme disease, human granulocytic anaplasmosis, and babesiosis: clinical practice guidelines by the Infectious Diseases Society of America. Clin Infect Dis 2006;43:1089--134.
10. Halperin JJ, Shapiro ED, Logigian E, et al. Practice parameter: treatment of nervous system Lyme disease (an evidence-based review). Report of the Quality Standards Subcommittee of the American Academy of Neurology. Neurology 2007; e-published ahead of print. Available at http://www.neurology.org/cgi/rapidpdf/01.wnl.0000265517.66976.28v1.pdf.

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Date last reviewed: 6/14/2007