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BACKGROUND: Human ehrlichiosis is a potentially fatal tickborne disease caused by Ehrlichia species, including E. chaffeensis and E. ewingii. Symptoms may include fever, headache, or rash. Early and empiric treatment with doxycycline is recommended for patients of all ages whenever ehrlichiosis is suspected. The primary vector in the U.S. is the lone star tick, Amblyomma americanum. Ehrlichiosis was made nationally notifiable in 1999. In 2008 the case definition changed to include categories for E. chaffeensis and E. ewingii infections. Presented here is a summary of passive surveillance of E. chaffeensis and E. ewingiiinfections in the U.S. during 2008–2012.
METHODS: Cases of ehrlichiosis are reported to CDC through two national surveillance systems: the Nationally Notifiable Diseases Surveillance System (NNDSS) and Case Report Forms (CRF). Demographic data were reported through NNDSS and used to calculate incidence rates. Additional data were reported through CRFs including immunosuppressive conditions, patient outcome, and laboratory results.
RESULTS: During 2008–2012, 4,563 cases of E. chaffeensis infection were reported through NNDSS (56.4% male, 64.2% white, 2.0% Hispanic). The incidence rate (IR) was 3.2 cases per million person-years (PY). States with the highest IR included Oklahoma (30.9), Missouri (26.3), Delaware (19.8), and Arkansas (19.4).The IR was highest among persons ages 65–69 (IR=7.9). Most cases were reported in May–July (n=2,947, 64.6%). The hospitalization rate was 57.4%, and the case fatality rate (CFR) was 1.0%. Children aged <5 years had the highest CFR of 3.6%. During 2008–2012, 53 cases of E. ewingiiinfection were reported through NNDSS (50.9% male, 66.0% white). The national IR was 0.04 cases per million PY. The hospitalization rate was 76.9%; no deaths were reported. Immunosuppressive conditions were reported by 26.3% of patients.
CONCLUSIONS: The overall rate for ehrlichiosis has increased since 1999. Although previous literature suggests E. ewingii primarily affects those who are immunocompromised, this report shows most cases occurred among immunocompetent cases. This is the first report to show children aged <5 years with ehrlichiosis have an increased CFR, relative to older patients. A recent survey demonstrated clinicians may be less willing to prescribe doxycycline to children aged <8 years compared to adults for suspected cases of Rocky Mountain spotted fever. A similar gap between recommendations and practice may explain part of the increased CRF among children with suspected ehrlichiosis. Ongoing surveillance and reporting of tickborne diseases are critical to inform public health practice and guide disease prevention efforts.