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. 2011 Jul;85(1):124-31.
doi: 10.4269/ajtmh.2011.10-0613.

Increasing incidence of Ehrlichia chaffeensis and Anaplasma phagocytophilum in the United States, 2000-2007

F Scott Dahlgren  1 , Eric J Mandel, John W Krebs, Robert F Massung, Jennifer H McQuiston
Affiliations

Increasing incidence of Ehrlichia chaffeensis and Anaplasma phagocytophilum in the United States, 2000-2007

F Scott Dahlgren et al. Am J Trop Med Hyg. 2011 Jul.

Abstract

Ehrlichia chaffeensis causes human monocytic ehrlichiosis, and Anaplasma phagocytophilum causes human granulocytic anaplasmosis. These related tick-borne rickettsial organisms can cause severe and fatal illness. During 2000-2007, the reported incidence rate of E. chaffeensis increased from 0.80 to 3.0 cases/million persons/year. The case-fatality rate was 1.9%, and the hospitalization rate was 49%. During 2000-2007, the reported incidence of A. phagocytophilum increased from 1.4 to 3.0 cases/million persons/year. The case-fatality rate was 0.6%, and the hospitalization rate was 36%. Rates among female patients were lower than among male patients for ehrlichiosis (rate ratio = 0.68) and anaplasmosis (rate ratio = 0.70). Most (80%) ehrlichiosis and anaplasmosis cases met only a probable case definition, although, use of a polymerase chain reaction to confirm infections increased during 2000-2007. Heightened reporting of these diseases will likely continue with improving recognition, changing surveillance practices, and appropriate application of diagnostic assays.

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Figures

Figure 1.
Figure 1.
County level incidence rates of A, Ehrlichia chaffeensis (n = 3,116), B, Anaplasma phagocytophilum (n = 4,116), and C, undetermined, unspecified, or other agent (n = 819) as reported to the National Electronic Telecommunications System for Surveillance, United States, 2000–2007. Incidence rates are cases per million persons per year.
Figure 2.
Figure 2.
Annual incidence rates of Ehrlichia chaffeensis (n = 3,126), Anaplasma phagocytophilum (n = 4,271), and undetermined, unspecified, or other agent (n = 824) as reported to the National Electronic Telecommunications System for Surveillance, United States, 2000–2007. Incidence rates are cases per million persons per year.
Figure 3.
Figure 3.
Incidence rates by age group of Ehrlichia chaffeensis (n = 3,103), Anaplasma phagocytophilum (n = 4,135), and undetermined, unspecified, or other agent (n = 782) as reported to the National Electronic Telecommunications System for Surveillance, United States, 2000–2007. Incidence rates are cases per million persons per year.
Figure 4.
Figure 4.
Case counts by month of onset of Ehrlichia chaffeensis (n = 2,365), Anaplasma phagocytophilum (n = 3,224), and undetermined, unspecified, or other agent (n = 723) as reported to the National Electronic Telecommunications System for Surveillance, United States, 2000–2007.
Figure 5.
Figure 5.
Proportion of cases hospitalized by age group of Ehrlichia chaffeensis (n = 1,141), Anaplasma phagocytophilum (n = 1,827), and undetermined, unspecified, or other agent (n = 630) as reported through Case Report Forms, United States, 2000–2007.
Figure 6.
Figure 6.
Number of annual cases of A, Ehrlichia chaffeensis (n = 1,191) and B, Anaplasma phagocytophilum (n = 2,035), reported through Case Report Forms (CRFs), United States, 2000–2007. The annual number of cases are subdivided into polymerase chain reaction (PCR)–positive cases, PCR-negative cases, and cases in which PCR was not performed. The annotation above each vertical bar is the annual percent of reported cases diagnosed by using PCR. Because the Centers for Disease Control and Prevention began collecting CRFs in 2000, few cases were reported in 2000.
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