Ehrlichiosis epidemiology and demographics

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Overview

Ehrlichiosis was deemed a reportable disease by the United States Center for Disease Control and Prevention in 1999. Since the year 2000 the number of reported cases has increased from 200 (in 2000) to 961 in 2008. However it should be noted that amount of reported cases was lessened in 2010.

The majority of cases are currently reported in Oklahoma, Missouri, and Arkansas. Other endemic areas include the South central and Southeastern United States. Incidents are highest among males and adults between the ages of 60 to 64 years of age. Cases have also been reported at higher rates among individuals with compromised immune systems.

Epidemiology and Demographics

Incidence

• First recognized as a reportable disease by the United States Center for Disease Control and Prevention in the late 1999.
• Numbers of reported cases have increased from 200 in 2000 to 961 in 2008.
• Incidence has fluctuated between 200-2010:
  • 2000- 1 case per million persons
  • 2008- 3.4 cases per million persons
  • 2010- 2.5 cases per million persons

The graph displays the number of human cases of ehrlichiosis cases reported to CDC annually from 1994 through 2010. Cases of ehrlichiosis have increased steadily from 200 cases in 2000, when the disease became nationally notifiable, to 961 cases in 2008. Cases decreased significantly in 2010 from 944 reported in 2009 to 740 reported in 2010.

Endemic Regions

• The lone star tick (Amblyomma americanum) is the primary vector of both Ehrlichia chaffeensis and Ehrlichia ewingii in the United States.

• • E. chaffeensis is most common in the south central and southeastern states.
  • E. ewingii is most common in the south central and southeastern states.
  • A. muris is endemic to Missouri and Wisconsin.

• Ehrlichiosis is most prominent in Oklahoma, Missouri, and Arkansas, accounting for 30% of all national incidences.
• However incidences have been reported through the United States.

This figure shows the incidence of ehrlichicosis cases by state in 2010 per million persons. Ehrlichiosis was not notifiable in Alaska, Colorado, the District of Columbia, Hawaii, Idaho, Iowa, Nevada, New Mexico, North Dakota or Montana. The incidence rate was zero for Arizona, Connecticut, Indiana, Massachusetts, Oregon, South Dakota, Utah, Vermont, Washington, and Wyoming. Incidence ranged between 0.03 to 1 case per million persons for California, Florida, Louisiana, Michigan, Ohio, Pennsylvania, Rhode Island and Texas. Annual incidence ranged from 1 to 3.3 cases per million persons in Alabama, Georgia, Illinois, Kansas, Maine, Minnesota, Mississippi, Nebraska, New Hampshire, New York, South Carolina and West Virginia. The highest incidence rates, ranging from 3.3 to 26 cases per million persons were found in Arkansas, Delaware, Kentucky, Maryland, Missouri, New Jersey, North Carolina, Oklahoma, Tennessee, Virginia, and Wisconsin.

Demographics

• The highest incidence rate of Ehrlichiosis is observed among males and patients above the age of 50 years. (Highest rate of incidence reported among patients between the ages of 60 and 64.
• Higher rates of infection are also observed among individuals with a compromised immune system.

This figure shows the average annual incidence of ehrlichiosis per million persons by age groups for 2000 through 2010. The graph shows that cases have been reported in every age group with increased incidence as age increases. The highest rate of incidence, more than 4 cases per million persons, is seen in persons ages 60-64 years.