In the past 5 years, reported Lyme disease cases have doubled. The U.S. Centers for Disease Control (CDC) posted that, in 2009, there were 38,468 reported cases , which is up 9% from 2008. As well, Lyme cases have increased by 94%, almost doubling from 2004-2009.
Note: according to epidemiologists at the CDC, these reported cases are underestimated 6- to 12-fold in endemic regions due to flaws in its reporting system.  Thus, the real number of new cases of Lyme disease in 2009 may be more like 461,616.
Here are some of the reasons for this large gap in numbers:
1. Inaccurate Lyme tests 
2. Physicians failing to report cases
3. A process that mandates that local health officials get in touch with each individual physician to confirm the details of many of the case reports 
4. Lyme disease cases that are rejected because they don’t fit the conservative surveillance definition of Lyme disease – one that is still based on an inaccurate blood test, a Lyme disease symptoms list that is outdated, and a burdensome reporting process for state and local health departments.
As well, the CDC does not report probable and suspected cases of Lyme disease to the media, only confirmed cases. The CDC also does not report the fact that their own epidemiologists say that the actual case count of Lyme disease could be ten times higher than the reported cases.
The result of this is that the average physician makes his/her diagnostic decisions based on the CDC case numbers, and when cases in their states are underestimated, more Lyme patients will be misdiagnosed. Funding for research on Lyme disease that is allocated by Congress is based on the CDC case numbers, too, and by underestimating these numbers by a factor of ten, grants will go to other diseases.
 Coulter, P, et. al. 2005. Two-Year Evalution of Borrelia burgdoferi Culture and Supplemental Test for Definitive Diagnosis of Lyme Disease, Clin. J. Clin. Microbiol. 41: 5080-5084. “…no single test is optimal for Lyme disease diagnosis”
(Source: Under Our Skin)