Each year, approximately 30,000 cases of Lyme disease are reported to CDC by state health departments and the District of Columbia. However, this number does not reflect every case of Lyme disease that is diagnosed in the United States every year.
Surveillance systems provide vital information but they do not capture every illness. Because only a fraction of illnesses are reported, researchers need to estimate the total burden of illness to set public health goals, allocate resources, and measure the economic impact of disease. CDC uses the best data available and makes reasonable adjustments—based on related data, previous study results, and common assumptions—to account for missing pieces of information.
To improve public health, CDC wants to know how many people are actually diagnosed with Lyme disease each year and for this reason has conducted two studies:
- Project 1 (Lyme Disease Testing by Large Commercial Laboratories in the United States) estimated the number of people who tested positive for Lyme disease based on data obtained from a survey of clinical laboratories. Researchers estimated that 288,000 (range 240,000–444,000) infections occur among patients for whom a laboratory specimen was submitted in 2008.
- Project 2 (Incidence of Clinician-Diagnosed Lyme Disease, United States, 2005-2010) estimated the number of people diagnosed with Lyme disease based on medical claims information from a large insurance database. In this study, researchers estimated that 329,000 (range 296,000–376,000) cases of Lyme disease occur annually in the United States.
Results of these studies suggest that the number of people diagnosed with Lyme disease each year in the United States is around 300,000. Notably, these estimates do not affect our understanding of the geographic distribution of Lyme disease. Lyme disease cases are concentrated in the Northeast and upper Midwest, with 14 states accounting for over 96% of cases reported to CDC. The results obtained using the new estimation methods mirror the geographic distribution of cases that is shown by national surveillance.