The Characteristics and Clinical Course of Patients with Scrub Typhus and Queensland Tick Typhus Infection Requiring Intensive Care Unit Admission: A 23-year Case Series from Queensland, Tropical Australia

Abstract

Scrub typhus and Queensland tick typhus (QTT)-rickettsial infections endemic to tropical Australia-can cause life-threatening disease. This retrospective study examined the clinical course of all patients with laboratoryconfirmed scrub typhus or QTT admitted to the intensive care unit (ICU) of a tertiary referral hospital in tropical Australia between 1997 and 2019. Of the 22 patients, 13 had scrub typhus and nine had QTT. The patients' median (interquartile range [IQR]) age was 50 (38-67) years; 14/22 (64%) had no comorbidity. Patients presented a median (IQR) of seven (5-10) days after symptom onset. Median (IQR) Acute Physiology and Chronic Health Evaluation II scores were 13 (9-17) for scrub typhus and 13 (10-15) for QTT cases (P = 0.61). Following hospital admission, the median (IQR) time to ICU admission was five (2-19) hours. The median (IQR, range) length of ICU stay was 4.4 (2.9-15.9, 0.8-33.8) days. Multi-organ support was required in 11/22 (50%), 5/22 (22%) required only vasopressor support, 2/22 (9%) required only invasive ventilation, and 4/22 (18%) were admitted for monitoring. Patients were ventilated using protective lung strategies, and fluid management was conservative. Standard vasopressors were used, indications for renal replacement therapy were conventional, and blood product usage was restrictive; 9/22 (41%) received corticosteroids. One patient with QTT died, and two (8%) additional patients with QTT developed purpura fulminans requiring digital amputation. Death or permanent disability occurred in 3/9 (33%) QTT and 0/13 scrub typhus cases (P = 0.055). Queensland tick typhus and scrub typhus can cause multi-organ failure requiring ICU care in otherwise well individuals. Queensland tick typhus appears to have a more severe clinical phenotype than previously believed.

The Applicability of Commonly Used Severity of Illness Scores to Tropical Infections in Australia

“…The study only reflects clinical management strategies used at this center which evolved significantly over the study period. 11,12 There were only 21 cases with rickettsial disease, and this group included patients with both scrub typhus and QTT, conditions caused by different pathogens. Some rickettsiologists may take issue with this approach.…”

“…31 Rickettsial infection was diagnosed if there was a clinical diagnosis of O. tsutsugamushi or R. australis infection accompanied by a positive polymerase chain reaction (PCR), a 4-fold rise in titers of paired serological samples (confirmed infection) or a single serological titer $128 with a clinically compatible syndrome (two or more of fever, rash, eschar, myalgia, or headache with no convincing alternative diagnosis) (probable infection). 12 Demographic, clinical, and laboratory data were collected from electronic and paper medical records. The study's primary endpoint was death before ICU discharge.…”

“…4,[7][8][9] These tropical pathogens can lead to multi-organ involvement with concurrent-sometimes dramatic-derangement in clinical and laboratory indices. [10][11][12] This results in significant elevation of the severity of illness (SOI) scores that are routinely calculated to estimate mortality risk in the critical care population. 13 While SOI scores have no role in the management of individual patients, they permit quantitative assessment of an intensive care unit's (ICU) performance, allowing comparison between institutions.…”

Scrub Typhus and Other Rickettsial Infections

“…Multiple organ dysfunction syndromes (MODS) are reported frequently (34–50%) in patients with rickettsial infections, and 18 to 30% of these patients require ventilatory support. 4 , 5 …”

“…Multiple studies have shown that delays in the recognition and administration of appropriate antibiotic therapy increase the chance of severe disease, whereas early diagnosis and appropriate management of complications improve outcomes. 5 – 7 Hence, in order to reduce morbidity and mortality due to rickettsial infections, there needs to be a high clinical suspicion of these infections in the presence of epidemiological data and clinical manifestations, such as rash, eschar, and multi-organ involvement. Further, laboratory clues, such as elevated liver enzymes, thrombocytopenia, and normal or mildly elevated white blood counts, should prompt the diagnosis of rickettsial infections, and appropriate treatment needs to be initiated as soon as possible.…”