Prevalence of relative bradycardia in Orientia tsutsugamushi infection.

We investigated 100 febrile patients infected with Orientia tsutsugamushi (the etiologic agent of scrub typhus) for the presence of relative bradycardia, defined as in increase in heart rate of < 10 beats/minutes/1 degree C increase in temperature. The median heart rate response for the entire febrile scrub typhus population was 9.3 beats/minute/degrees C and the prevalence of relative bradycardia was 53%. The occurrence of relative bradycardia was independent of patient age or gender. There were no differences in median basal temperature or febrile temperature between those patients exhibiting relative bradycardia and those with a normal febrile pulse increase. However, febrile patients with relative bradycardia had a significantly higher resting pulse rate following recovery from infection than did patients who had a normal pulse increase during their illness. These data demonstrate that relative bradycardia frequently accompanies mild infection with O. tsutsugamushi and that baseline cardiovascular parameters may affect the febrile heart rate response to scrub typhus.