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Volume 18, Number 10—October 2012
Letter

Rickettsia parkeri and Candidatus Rickettsia andeanae in Gulf Coast Ticks, Mississippi, USA

Flavia A.G. Ferrari, Jerome Goddard, Christopher D. Paddock, and Andrea S. Varela-StokesComments to Author 
Author affiliations: Mississippi State University, Mississippi State, Mississippi, USA (F.A.G. Ferrari, J. Goddard, A.S. Varela-Stokes); and Centers for Disease Control and Prevention, Atlanta, Georgia, USA (C.D. Paddock)

Main Article

Table

PCR results for adult Rickettsia parkeri– and Candidatus Rickettsia andeanae–infected Gulf Coast ticks (Amblyomma maculatum) collected from 10 sites in Mississippi, USA, 2008–2010*

Location (no. collection sites) No. ticks No. (%; 95% CI) SFG rompA No. (%; 95% CI) R. parkeri only No. (%; 95% CI) Candidatus R. andeanae only Expected no. (%) co-infected ticks No. (%; 95% CI) co-infected ticks
North (4) 257 49 (19.1; 14.5–24.4)† 48 (18.7; 14.1–24)‡ 0§ 0.19 (0.07) 1 (0.4; 0–2.1)¶
Central (1) 38 4 (10.5; NA) 1 (2.6; NA) 2 (5.3; NA) 0.16 (0.42) 1 (2.6; NA)
South (5) 403 75 (18.6; 14.9–22.8)† 57 (14.1; 10.9–17.9)‡ 8 (2.0; 0.9–3.9)§ 2.99 (0.74) 10 (2.5; 1.2–4.5)¶
Total (10) 698 128 (18.3; NA) 106 (15.2; NA) 10 (1.4; NA) 3.65 (0.52) 12 (1.7; NA)

*The estimated value of co-infection caused by chance alone (E) was calculated by using the formula E = (a + b)(a + c) / (a + b + c + d) (5), where a = no. ticks infected with both Rickettsia species, b = no. ticks infected only with R. parkeri, c = no. ticks infected only with Candidatus R. andeanae, and d = no. ticks not infected with either Rickettsia species. SFG rompA, spotted fever group rickettsial outer membrane protein A gene. NA, not applicable.
†p = 0.9187.
‡p = 0.1275.
§p = 0.0257.
¶p = 0.0578 (comparison of prevalence from northern and southern sites only).

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References
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The conclusions, findings, and opinions expressed by authors contributing to this journal do not necessarily reflect the official position of the U.S. Department of Health and Human Services, the Public Health Service, the Centers for Disease Control and Prevention, or the authors' affiliated institutions. Use of trade names is for identification only and does not imply endorsement by any of the groups named above.
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