Abstract
Queensland tick typhus (QTT; Rickettsia australis) is an important cause of community-acquired acute febrile illness in eastern Australia. Cases of QTT were identified retrospectively from 2000 to 2015 at five sites in Northern Brisbane through a pathology database. Those included had a fourfold rise in spotted fever group (SFG)-specific serology, a single SFG-specific serology ≥ 256 or SFG-specific serology ≥ 128 with a clinically consistent illness. Cases were excluded on the basis of clinical unlikelihood of QTT infection. Thirty-six cases were included. Fever was found in 34/36 (94%) patients. Rash occurred in 83% of patients with maculopapular being the dominant morphology (70%). Thrombocytopenia, lymphopenia, and raised transaminases were common and occurred in 58%, 69%, and 89% of patients, respectively. Thirty-one of 36 (86%) patients received antibiotic therapy (usually doxycycline) and the time to correct antibiotic (from admission) ranged from 3 to 120 h (mean 45.5 h). Four of 36 (11%) required intensive care unit (ICU) admission for severe sepsis and end-organ support. There were no deaths. QTT has a wide range of clinical and laboratory features. Early and appropriate antimicrobial therapy is important and may prevent severe disease. Further prospective studies are required to identify factors associated with severe infection and sepsis.
Highlights
Queensland tick typhus (QTT) is an ill-recognized tick-borne disease that occurs along the eastern coast of Australia [1]
The causative organism, Rickettsia australis, is one of 19 known pathogenic Rickettsia species worldwide and one of three spotted fever group (SFG) rickettsial infections that occur in Australia, the other two species being R. honei (Flinders Island spotted fever) and R. honei sub sp. marmionii (Australian spotted fever) [1,2]
Laboratory and clinical manifestations of SFG infections in Australia were evaluated by Sexton et al (1991) and provide the basis for our current understanding of QTT [4]
Summary
Queensland tick typhus (QTT) is an ill-recognized tick-borne disease that occurs along the eastern coast of Australia [1]. The causative organism, Rickettsia australis, is one of 19 known pathogenic Rickettsia species worldwide and one of three spotted fever group (SFG) rickettsial infections that occur in Australia, the other two species being R. honei (Flinders Island spotted fever) and R. honei sub sp. Clinical illness is often non-specific and difficult to diagnose, with severity ranging from a mild self-limiting illness to fulminant disease and sepsis, including death [3]. Recent case reports and series have demonstrated the occurrence of more severe disease and complications, shifting the paradigm from the short-lived, mild flu-like illness that was originally described in the retrospective review by Sexton et al in 1990 [4,5,6]
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