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

Abstract

Introduction: Clinicians are commonly taught that if patients with suspected rickettsial disease have continuing fever after 48 h 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 (TTD) after the initiation of the patients' anti-rickettsial therapy. It also identified factors associated with delayed defervescence (TTD >48 h 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 h (p = 0.05). Patients with delayed defervescence were more likely to require Intensive Care Unit (ICU) admission than those who defervesced within 48 h (12/32 (38%) versus 3/26 (12%) and p = 0.02). Even among patients not requiring ICU care, patients with delayed defervescence required a longer hospitalisation than those who defervesced within 48 h (median (IQR): 6 (3-8) versus 3 (2-5) days and p = 0.006). Conclusions: A significant proportion of patients with confirmed scrub typhus and QTT will remain febrile for >48 h after appropriate anti-rickettsial therapy. Delayed defervescence is more common in patients with severe disease.

An Update on the Laboratory Diagnosis of Rickettsia spp. Infection

“…When a rickettsial infection is considered within the differential and anti-rickettsial antibiotics are commenced, defervescence within 48 h is often used as a diagnostic test [ 22 ]. However, a significant proportion of patients with confirmed rickettsial infections may have persisting fevers past this time point, particularly in severe disease [ 24 ]. Laboratory diagnosis relies heavily on serology, with interpretation of results dependent on appropriate epidemiology, a clinically compatible illness, and the phase of rickettsial disease when testing occurs [ 22 ].…”