One can guess—pick CDC’s annual count and multiple by 10—or one can do the hard work of actually counting.
Advanced Laboratory Services marketing materials state, "The CDC estimates that in the USA there are more than 300,000 new cases each year and there may be as many as 4 million people currently infected." Dr. Mead said that this is incorrect: The CDC expects about 30,000 new cases of Lyme disease per year, and the agency is currently developing updated estimates for nation-wide prevalence.
(Excerpt from: Lyme Culture Test Causes Uproar. Medscape.com. by Janis C. Kelly, Jan 30, 2013.)
Each year, more than 30,000 cases of Lyme disease are reported to CDC, making it the most commonly reported tick-borne illness in the United States. The new estimate suggests that the total number of people diagnosed with Lyme disease is roughly 10 times higher than the yearly reported number. This new estimate supports studies published in the 1990s indicating that the true number of cases is between 3- and 12-fold higher than the number of reported cases.
(Excerpt from: Aug. 19, 2013 CDC Press Release.)
Last year, the Centers for Disease Control and Prevention reported that thirty thousand Americans were diagnosed with Lyme disease, the most commonly reported tick-borne illness in the United States. Today, it bumped the number a bit—to “around” [300,000]. The shocking difference is not as bizarre as it might seem. The C.D.C. has always said that the lower number represented solely those diagnoses confirmed by laboratories or reported by physicians; officials acknowledged that the real case load was higher.
Excerpt from: The New Yorker, August 19, 2013, Lyme Disease’s Staggering New Numbers.)
CDC- “Surveillance for LD is subject to several limitations. Studies from the early 1990s suggested that LD cases were underreported by six to 12-fold in some areas where LD is endemic (2,3); the current degree of underreporting for national data is unknown. In addition, differences in the demographics of reported cases among states with above- and below-average incidence suggest variation in diagnostic and reporting practices among states. Clinicians are reminded that the LD case definition was developed for surveillance purposes and might not be appropriate for clinical management of individual patients (1).”
2. Meek JI, Roberts CL, Smith EV Jr, Cartter ML. Underreporting of Lyme disease by Connecticut physicians, 1992. J Public Health Manage Pract 1996;2:61--5.
3. Coyle BS, Strickland GT, Liang YY, Pena C, McCarter R, Israel E. The public health impact of Lyme disease in Maryland. J Infect Dis 1996;173:1260--2.