Background: Lyme disease is the most commonly reported vector borne disease in the United States and is a major public health concern in Maine. Maine Center for Disease Control and Prevention (Maine CDC) monitors Lyme disease through a passive surveillance system. In order to validate the Lyme disease surveillance system, Maine CDC was interested in comparing trends with a secondary data source. Specifically, Maine CDC was interested in comparing trends by age group, gender, geography, and timelines. Also, because hospitalization due to Lyme disease is rare, this analysis provided an opportunity to look at the diagnosis codes used for Lyme disease visits. The purpose of this paper is to compare the data acquired through surveillance to a secondary data source in order to evaluate the completeness of the data and verify trends.
Methods: Surveillance data was extracted from Maine’s NEDSS Base System for the years 2008 – 2011. Only confirmed and probable cases were included in data analysis. The Maine Health Data Organization (MHDO) collects information on all hospital inpatient and outpatient data visits and was used for this comparison. MHDO inpatient and outpatient hospital encounters with a diagnosis of 08881 in any diagnosis field were extracted from the full dataset from 2008 – 2011.
Results: Surveillance data showed the 5-14 year old age group had the highest rates of Lyme disease while outpatient data showed adults over the age of 45 to have the highest rates. Outpatient data showed a higher percentage of females with Lyme disease visits. Geographic trends did not match well between surveillance data and MHDO data which may be due to the hospital being used as proxy for the patient address. Timeliness trends were consistent between all sources, with the majority of Lyme disease occurring in the summer months of June, July and August. The majority of outpatient visits had Lyme disease listed as their primary diagnosis while the majority of inpatient visits had Lyme disease as a secondary or lower diagnosis.
Conclusions: There were several limitations to this study including incomplete data, and the inability to differentiate between new and old Lyme diagnoses. There is reasonably good similarity in the trends of these two systems helping validate the usefulness of Maine’s Lyme disease surveillance system. Many of the discrepancies warrant further investigation, and may lead to future opportunities for education or improvement in Lyme disease surveillance.