Prompt defervescence after initiation of treatment for rickettsial infections - time to dispense with the dogma?

INTRODUCTION:Clinicians are commonly taught that if patients with suspected rickettsial disease have continuing fever after 48 hours of anti-rickettsial therapy, an alternative diagnosis is likely. METHODS:This retrospective study of patients hospitalised with scrub typhus and Queensland tick typhus (QTT) in tropical Australia, examined the time to defervescence after initiation of the patients' anti-rickettsial therapy. It also identified factors associated with delayed defervescence (time to defervescence >48 hours after antibiotic commencement). RESULTS:Of the 58 patients, 32 (56%) had delayed defervescence. The median (interquartile range (IQR)) age of patients with delayed defervescence was 52 (37-62) versus 40 (28-53) years in those who defervesced within 48 hours (p = 0.05). Patients with delayed defervescence were more likely to require Intensive Care Unit (ICU) admission than those who defervesced within 48 hours (12/32 (38%) versus 3/26 (12%), p = 0.02). Even among patients not requiring ICU care, patients with delayed defervescence required a longer hospitalisation than that those who defervesced within 48 hours (median (IQR): 6 (3-8) versus 3 (2-5) days, p = 0.006). CONCLUSIONS:A significant proportion of patients with confirmed scrub typhus and QTT will remain febrile for >48 hours after appropriate anti-rickettsial therapy. Delayed defervescence is more common in patients with severe disease.