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

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. 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). 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). 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.

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