Effect of Surveillance Method on Reported Characteristics of Lyme Disease, Connecticut, 1996–2007

Starr-Hope Ertel

, Randall S. Nelson, and Matthew L. Cartter

Author affiliations: Connecticut Department of Public Health, Hartford, Connecticut, USA

Abstract

To determine the effect of changing public health surveillance methods on the reported epidemiology of Lyme disease, we analyzed Connecticut data for 1996–2007. Data were stratified by 4 surveillance methods and compared. A total of 87,174 reports were received that included 79,896 potential cases. Variations based on surveillance methods were seen. Cases reported through physician-based surveillance were significantly more likely to be classified as confirmed; such case-patients were significantly more likely to have symptoms of erythema migrans only and to have illness onset during summer months. Case-patients reported through laboratory-based surveillance were significantly more likely to have late manifestations only and to be older. Use of multiple surveillance methods provided a more complete clinical and demographic description of cases but lacked efficiency. When interpreting data, changes in surveillance method must be considered.

Lyme disease, a multisystem disease caused by the spirochete bacterium Borrelia burgdorferi, is the most commonly reported vector-borne disease in Connecticut and in the United States (1). During 1996–2007, Connecticut contributed 33,457 (15%) cases to the national surveillance case count, with a mean of 83.4 cases per 100,000 population reported annually, and consistently led the nation in reported annual incidence rate during the study period (2). Diagnosis of Lyme disease is based on clinical findings, serologic evidence of infection, and history of exposure to Ixodes scapularis ticks. Early stages of illness are most readily diagnosed by identification of erythema migrans. Later-stage illness can involve the musculoskeletal, neurologic, or cardiovascular systems. Positive serologic results are necessary for identifying and classifying patients with later manifestations.

During 1996–2007, the Connecticut Department of Public Health (CDPH) received Lyme disease reports through 4 surveillance methods: passive physician, active physician, enhanced laboratory, and mandatory laboratory. Physician-based surveillance (passive and active) was conducted during the entire study period and relied on health care providers to report new diagnoses of Lyme disease. Active surveillance comprised a voluntary network of health care providers who reported cases 1× per month. Enhanced laboratory surveillance, conducted during 1996–1997, required participating Connecticut laboratories to send supplemental case report forms with each positive B. burgdorferi result to the ordering physician. In January 1998, to study the effectiveness of a newly released Lyme disease vaccine, mandatory laboratory surveillance was implemented that required all laboratories to report positive and equivocal results to CDPH. Follow-up, conducted by CDPH staff, involved sending a letter and supplemental report form to the ordering physician. To assist the physician, demographic and patient-identifying information from the laboratory report was incorporated into the form. Mandatory laboratory surveillance ended after 2002 when the Lyme disease vaccine was removed from the market. In 2007, mandatory reporting of positive Lyme disease results was reinstated for laboratories with electronic reporting capability. Two large commercial laboratories provided electronic reports. Follow-up was reestablished by using the previous method, i.e., CDPH staff sent a letter and supplemental report form to the ordering physician.

Public health surveillance methods for infectious diseases change over time, depending on program priorities and resources, advancements in diagnostic testing, modifications to surveillance case definitions, and changing reporting modalities (e.g., electronic laboratory reporting). Lyme disease surveillance data provide a measure of the relative geographic distribution of this disease and its effect on public health in Connecticut and have been used to assess the effectiveness of control and prevention activities (3–5). These data also form part of the risk communication messages provided to the general public, advocacy groups, media, political leaders, health care providers, and public health professionals. We examined how surveillance method affected the classification of reported clinical and demographic characteristics of case-patients and the incidence of Lyme disease in Connecticut, during 1996–2007.