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Reported cases of Lyme disease in Hunterdon County, New Jersey, increased almost 200% from 75 (67/100,000 population) in 1992 to 216 (193/100,000 population) in 1993. For evaluation of risk factors for Lyme disease and for determination of the cause of this increase, a case-control study was conducted, and the reporting practices of physicians' offices were evaluated. For cases reported in 1993, age and sex distribution, month of disease onset, and proportion of cases with erythema migrans rash were within expected limits. Analysis of age-matched case-control data showed that rural residence; clearing periresidential brush during spring and summer months; and the presence of rock walls, woods, deer, or a bird feeder on residential property were associated with incident Lyme disease. A review of physician reporting patterns suggested that the increase in reported cases in 1993 was due to improved reporting as well as to an increase in the numbers of patients diagnosed with Lyme disease. In addition, substantial underreporting of Lyme disease by physicians' offices was found.

Treatment of unsubstantiated Lyme disease has led to serious complications in some cases. Two case-control studies, based on information in clinical records of patients discharged with a diagnosis of Lyme disease during 1990-1992, were conducted at a central New Jersey hospital. Twenty-five patients with biliary disease were identified, and 52 controls were selected from 1352 patients with suspected Lyme disease. Only 3% of 71 evaluatable subjects met the study criteria for disseminated Lyme disease. Patients with biliary disease were more likely than were antibiotic controls to have received ceftriaxone and more likely than ceftriaxone controls to have received a daily ceftriaxone dose > or = 40 mg/kg and to be < or = 18 years old. Fourteen of 25 biliary case-patients underwent cholecystectomy; all had histopathologic evidence of cholecystitis and 12 had gallstones. Thus, treatment of unsubstantiated diagnoses of Lyme disease is associated with biliary complications.