June 2000
ATLANTA -Reported cases of Lyme disease increased by 70% between 1992 and 1998, and 10 states were responsible for 92% of reported cases, according to Centers for Disease Control and Prevention (CDC) surveillance. These findings will help patient evaluation and provide more targeted prevention techniques, including use of the Lyme disease vaccine (LYMErix, SmithKline Beecham).
The total number of reported cases during the surveillance period was 88,967. The number of cases increased from 9,896 in 1992 to 16,802 in 1998.
"Mostly this is due to an increasing intensity of exposure at those sites where we've known that Lyme disease has been endemic for a while, but also that there is some evidence of geographic spread," said David T. Dennis, MD, MPH, medical epidemiologist and coordinator of the CDC's Lyme disease program.
"We don't see a change in the trend of increasing incidence," he said. This won't happen until the means to control the ticks that transmit the disease become more effective.
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Children are at greater risk during the spring and summer months because of the increased time spent outdoors. The CDC surveillance showed that disease onset occurred in every month of the year, but was most frequent in June, July and August. This time of year is also consistent with the feeding activity of Ixodes scapularis, he primary vector of Lyme disease. Increases in I. scapularisand Ixodes pacificuscarrying Borrelia burgdorferiin endemic regions was reported. However, public education about the risk of tick exposure also increased within the study period, according to CDC data.
The data showed children ages 5 to 9 had the third largest incidence rate. "We believe that is due to a greater activity in tick-infested areas. It also relates to the fact that most cases of Lyme disease in the United States are acquired in the residential environment," Dennis said. In children and adolescents 5 to 19 years of age, males had a higher incidence rate.
Even children ages 0 to 4 had significant levels of incidence. "We start seeing cases in children 1 to 2 years of age, which means that some children are probably being exposed in the maintained part of their yards," he said.
The Lyme disease vaccine is indicated for use in patients 15 to 70 years old who live in high-risk areas. "The vaccine is not yet available for children younger than 15, but we anticipate that it probably will be sometime in the next year or so. That is something that parents of children living in highly endemic areas may wish to discuss with their physician," said Dennis.
Despite the growing number of cases reported, the total number of counties that reported Lyme disease did not increase, suggesting that the rise in cases came from areas already known to be Lyme-endemic. Most cases were found in New York (32.8%), Connecticut (17.4%), Pennsylvania (14.6%), New Jersey (12.2%), Wisconsin (3.6%) and Rhode Island (3.5%).
"If a person is in a highly endemic area, then 25% to 50% of deer ticks will contain the bacteria that cause Lyme disease," said Dennis. In New York, 81.9% of cases with known county of origin came from only five of the state's 62 counties.
Misdiagnosis and inappropriate treatment can be a significant problem. Targeting only those regions at the highest risk can make efficient use of limited resources. Physicians should always consider "the prior probability of disease" when examining a patient for possible Lyme disease infection, according to the CDC report. Prior probability can be determined by the risk of exposure in a certain community.
"People should be aware and educated about the risks. They should, rather than be routinely treated with antibiotics just for a tick bite, be sensitive to the development of signs and symptoms of illness. If they or their children develop those signs or symptoms after a bite, they should be seen promptly be a physician," said Dennis, who is also chief of the Bacterial Zoonoses Branch, Division of Vector-borne Infectious Diseases at the CDC.
A positive test result from a suspected case in a nonendemic region should be investigated as a possible false-positive result, according to the CDC report. Educating nonendemic populations about limited risks could decrease needless testing.
State health departments reported Lyme disease cases to the
CDC by using the National Electronic Telecommunications System for Surveillance
(NETSS). A reportable case was defined as illness diagnosed by a physician
(erythema migrans 
5 cm in
diameter) or having a musculoskeletal, neurologic or cardiac manifestation plus
laboratory confirmation of infection.
Because it is mostly reported through passive surveillance, Lyme disease is often underreported. Studies in Connecticut and Maryland showed that for every case of Lyme disease reported, seven to 12 cases go unreported. "For all nationally reportable diseases, there's considerable underreporting. It wouldn't surprise us if nationally there were three to five times the number of cases occurring than are being reported," said Dennis.
Modifying the environment of high-risk areas can help lessen Lyme disease incidence. The CDC is currently trying to reduce the density of I. scapularisand control deer populations in certain areas, according the report.
"One new element to decreasing tick population is host-targeted pesticides. We have devices that can target rodent reservoirs," said Dennis. This approach can eliminate ticks on mice and deer without widespread use of pesticides.
Individuals in high-risk areas are encouraged to avoid woody, brushy or overgrown grassy areas. "The most important element of personal protection is for parents, and children themselves, to know what areas are tick infested and at what times of the year they are most likely to be infested," said Dennis. "If people need to be in tick-infested areas, then they should take other personal protective measures, including use of repellants and protective clothing."
Because it takes 36 to 48 hours of tick attachment before B. burgdorferican be transmitted, parents should check their children at least once a day for ticks.
Early detection and treatment of suspected Lyme disease or other tick-borne infection is essential. "Lyme disease, if diagnosed and treated early in the course of infection in children, is readily cured without long-term sequelae or complications. The way to achieve this is through education of the public and of health care providers," Dennis said.
Further enhancement of Lyme disease surveillance and testing will help target preventive measures, including use of the vaccine.
For more information:
- CDC. Surveillance for Lyme disease - United States, 1992-1998. MMWR. 2000;49(SS-3):1-11.
- Meek JI, Roberts CL, Smith EV Jr, Cartter ML. Underreporting of Lyme disease by Connecticut physicians, 1992. Journal Public Health Management Practice. 1996;2:61-5.
- Coyle BS, Strickland GT, Liang YY, et al. Public impact of Lyme disease in Maryland. J Infect Dis. 1996;173:1260-2.
- Seltzer EG, Gerber MA, Cartter ML et al, Long-term outcomes of persons with Lyme disease JAMA. 2000;283:609-616.
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