Volume 23-16
August 15, 1997

[Table of Contents]

LYME DISEASE - UNITED STATES, 1996

Lyme disease (LD) is caused by the tickborne spirochete Borrelia burgdorferi sensu lato and is the most common vectorborne disease in the United States. Surveillance for LD was initiated by United States Centers for Disease Control and Prevention (CDC) in 1982, and the Council of State and Territorial Epidemiologists designated it a nationally notifiable disease in January 1991. For surveillance purposes, LD is defined as the presence of an erythema migrans rash ³ 5 cm in diameter or laboratory confirmation of infection with evidence of at least one manifestation of musculoskeletal, neurologic, or cardiovascular disease ⁽¹⁾. This report summarizes the provisional number of cases of LD reported to CDC during 1996 and indicates that the number of cases reported was a record high.

In 1996, a total of 16,461 cases of LD were reported to CDC by 45 states and the District of Columbia (overall incidence: 6.2 per 100,000 population^**), representing a 41% increase from the 11,700 cases reported in 1995 and a 26% increase from the 13,043 cases reported in 1994 (Figure 1). As in previous years, most cases were reported from the Mid-Atlantic, Northeast, and North Central regions. Eight states reported LD incidences that were higher than the overall national rate (Connecticut, 94.8; Rhode Island, 53.9; New York, 29.2; New Jersey, 27.4; Delaware, 23.9; Pennsylvania, 23.3; Maryland, 8.8; and Wisconsin, 7.7); these states accounted for 14,959 (91%) of the nationally reported cases. In 1996, zero cases were reported from five states (Alaska, Arizona, Colorado, Montana, and South Dakota).

Figure 1 Number of reported cases of Lyme disease, by year - United States, 1982-1996*

* Data for 1996 are provisional

Eighty-seven counties each reporting > 20 cases accounted for 89% of all reported cases. Reported incidences were > 100 per 100,000^**** in 18 counties in Connecticut, Maryland, Massachusetts, North Carolina, New Jersey, New York, Pennsylvania, Rhode Island, and Wisconsin; the highest reported county-specific incidence (1,247.5 per 100,000) was in Nantucket County, Massachusetts. From 1995 to 1996, a total of 28 states reported increases in the number of cases, 16 states reported decreases, and seven states reported no change. Approximately 90% of the total increase in reported cases in 1996 occurred in five states (Connecticut, New Jersey, New York, Pennsylvania, and Rhode Island) where average annual LD incidence rates had exceeded the national average for the previous 5 years combined. Of 5,298 cases for which information was available, 217 (4%) were reported as having been acquired outside of the United States, and 156 (3%) cases were reported as having been acquired in the United States but outside of the reporting state. The highest proportions of cases occurred among persons aged 0 to 14 years (3,784 [23%]) and adults aged 40 to 79 years (7,694 [47%]). Of 16,422 cases for which sex was reported, 8,634 (53%) were male.

MMWR Editorial Note

Increases in reported LD cases in 1996 were limited to certain counties in some states, consistent with focal differences in the distribution and density of the tick vector. In both Connecticut and Rhode Island, the numbers of reported cases of LD increased statewide, although increases were greatest in coastal counties. In both states, this increase was associated with increased population densities of I. scapularis (K. Stafford, Connecticut Agricultural Experiment Station, and T. Mather, University of Rhode Island: personal communications, 1997). In New York, the greatest increases occurred in Dutchess County, where reported cases of LD nearly doubled from 1995 (918) to 1996 (1,832). Because an LD vaccine trial was being conducted in the area, some of this increase may have resulted from heightened awareness and reporting of LD. The number of reported cases was stable in other counties of New York with endemic disease, including Putnam, Suffolk, and Westchester counties. In New Jersey, eight counties with active surveillance reported higher rates than the remaining counties with passive surveillance systems.

The increase in reported LD cases in 1996 probably represents a combination of increased tick density, enhanced health-care provider awareness and reporting, and improved laboratory surveillance. In addition, case reporting has been enhanced through the availability of CDC resources for LD surveillance in eight states (Connecticut, Michigan, Minnesota, New Jersey, New York, Oregon, Rhode Island, and West Virginia).

Most LD cases respond well to appropriate antibiotic therapy; drugs of choice include amoxicillin, doxycycline, and ceftriaxone ⁽²⁾ . Vaccines to prevent LD are under evaluation but are not yet available. Personal protection methods recommended for preventing cases of LD and other tickborne diseases (e.g. babesiosis, ehrlichiosis, and Rocky Mountain spotted fever) include wearing light-colored clothing (to more readily detect ticks), tucking long pants into socks, using insect repellents and acaricides according to label directions, and performing tick checks at least daily. The use of environmental modifications to residential properties (e.g. application of insecticides, use of deer fencing, and removal of leaf litter) also may help prevent LD.

References

1. CDC. Case definitions for infectious conditions under public health surveillance. MMWR 1997;46(no. RR-10):20-1.

2. Steere AC. Borrelia burgdorferi (Lyme disease, Lyme borreliosis).In: Mandell GL, Bennett JE, Dolin R, eds. Principles and practices of infectious diseases. New York : Churchill, Livingstone, 1995:2143-55.

Source : Morbidity and Mortality Weekly Report, Vol 46, No 23, 1997. ** State rates are based on 1996 population estimates **** County rates are based on 1990 population estimates

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