Epidemic curves of tick-related ED visits for each of the 6 MSAs were characterized by increased frequency in the spring and summer months followed by a decline in the fall. However, the pattern of doxycycline prescriptions varied by MSA. Doxycycline prescriptions in Durham-Chapel Hill and Raleigh-Cary MSAs increased in the spring and summer, while for the 4 other Piedmont MSAs there was no consistent or pronounced spring-summer increase.
Doxycycline prescription use did not always correlate well with suspected tick activity in North Carolina. Therefore, doxycycline prescription use cannot necessarily be used as a surrogate measure of tick activity for infectious disease surveillance until the reasons for this variability are better understood.
To compare the seasonal frequency of doxycycline prescriptions with tick-related emergency department (ED) visits in North Carolina, and to determine if doxycycline prescriptions are associated in time with an increase in the number of ED visits for a tick-related patient complaint or a subsequent diagnosis of a tick-borne infection.
Aggregate monthly counts of total dispensed doxycycline prescriptions for each North Carolina Piedmont Metropolitan Statistical Area (MSA) were compared with the proportions of tick-related ED visits from August 2007 through July 2009.