Epidemiology of human ehrlichiosis and anaplasmosis in the United States, 2001-2002.

During 2001 through 2002, 1,176 cases of the tick-borne diseases human monocytic ehrlichiosis (HME) and human granulocytic anaplasmosis (HGA) were reported to the Centers for Disease Control and Prevention (CDC) by 32 states through the National Electronic Telecommunications System for Surveillance. The average reported annual incidences for HME and HGA during 2001-2002 were 0.6 and 1.4 cases per million population, respectively; incidence was highest among men > 60 years of age. During this same interval, a total of 883 cases of HME and HGA were reported to CDC through a passive surveillance system of tick-borne disease case report forms (CRFs). The surveillance information retrieved from CRFs has allowed for qualitative evaluation of ehrlichiosis and anaplasmosis risk factors, severity, and diagnostic accuracy. Although these surveillance systems likely substantially under-represent the true burden of ehrlichiosis and anaplasmosis in the United States due to poor recognition and reporting, they represent the first compilation of national data since these diseases were made nationally notifiable. Continued and improved surveillance activities will progressively reinforce our understanding and awareness of these newly recognized zoonotic infections.