Factors associated with tick bites and pathogen prevalence in ticks parasitizing humans in Georgia, USA.

BACKGROUND: The incidence and emergence of tick-borne diseases has increased dramatically in the United States during the past 30 years, yet few large-scale epidemiological studies have been performed on individuals bitten by ticks. Epidemiological information, including disease development, may provide valuable information regarding effectiveness of tick bite prevention education, pathogen transmission, human-disease dynamics, and potential implications for under reporting of tick-borne diseases. METHODS: Ticks found attached to Georgia residents were submitted for identification and polymerase chain reaction (PCR) testing for Francisella tularensis, Ehrlichia, Anaplasma, Borrelia, and Rickettsia spp. Tick bite victims were interviewed three weeks after the tick bite to identify various epidemiologic factors associated with infestation and if signs suggestive of a tick-borne disease had developed. Fisher's exact test of independence was used to evaluate associations between various factors evaluated in the study. A multivariable logistic regression model was used for the prediction of non-specific illness post-tick bite. RESULTS: From April 2005-December 2006, 444 participants submitted 597 ticks (426 Amblyomma americanum, 142 Dermacentor variabilis, 19 A. maculatum, 7 Ixodes scapularis, 3 Amblyomma sp.) which originated from 95 counties. Only 25 (34 %) of 74 interviewed individuals purposely took tick bite prevention measures. Ticks that were PCR positive for bacterial organisms were attached to 136 participants. Of the 77 participants who developed non-specific illness, 50 did not have PCR positive ticks, whereas 27 did have PCR positive tick (s). Of those 27 individuals, 12 fit the criteria for a possible tick-borne illness (i.e., tick attached >6 h [if known], ≥4 day incubation period, and the individual exhibited clinical symptoms typical of a tick-borne illness without exhibiting cough, sore throat, or sinus congestion). Ticks from these individuals were positive for R. amblyommii (n = 8), E. ewingii (n = 1), R. montana (n = 1), R. rhiphicephali (n = 1), and Rickettsia sp. TR-39 (n = 1). CONCLUSIONS: Although illnesses reported in this study cannot definitively be connected with tick bites, it does provide insight into development, diagnosis, and treatment of possible tick-borne diseases post-tick bite. The study also provided data on pathogen prevalence, and epidemiologic factors associated with tick bites, as well as tick presence by county in Georgia.

Meningococcal carriage among Georgia and Maryland high school students.

BACKGROUND: Meningococcal disease incidence in the United States is at an all-time low. In a previous study of Georgia high school students, meningococcal carriage prevalence was 7%. The purpose of this study was to measure the impact of a meningococcal conjugate vaccine on serogroup Y meningococcal carriage and to define the dynamics of carriage in high school students. METHODS: This was a prospective cohort study at 8 high schools, 4 each in Maryland and Georgia, during a school year. Students at participating schools received quadrivalent meningococcal conjugate vaccine that uses diphtheria toxoid as the protein carrier (MCV4-DT). In each state, 2 high schools were randomly assigned for MCV4-DT receipt by students at the beginning of the study, and 2 were randomly assigned for MCV4-DT receipt at the end. Oropharyngeal swab cultures for meningococcal carriage were performed 3 times during the school year. RESULTS: Among 3311 students, the prevalence of meningococcal carriage was 3.21%-4.01%. Phenotypically nongroupable strains accounted for 88% of carriage isolates. There were only 5 observed acquisitions of serogroup Y strains during the study; therefore, the impact of MCV4-DT on meningococcal carriage could not be determined. CONCLUSIONS: Meningococcal carriage rates in US high school students were lower than expected, and the vast majority of strains did not express capsule. These findings may help explain the historically low incidence of meningococcal disease in the United States.