Respiratory manifestations of rickettsial disease in tropical Australia; Clinical course and implications for patient management.

BACKGROUND

Rickettsial infections have a global distribution and can cause life-threatening disease. Respiratory symptoms can be a harbinger of a more complicated disease course. However, the clinical associations - and the clinical course - of patients with rickettsial disease and respiratory involvement are incompletely defined.

METHODS

This was a retrospective study of all patients with a diagnosis of scrub typhus or Queensland tick typhus (QTT) managed at Cairns Hospital in tropical Australia, between 1st January 1997 and 31st October 2023. We determined the demographic, clinical, radiological and laboratory associations of respiratory involvement which was defined as any acute abnormality of lung parenchyma identified on thoracic imaging during their hospitalisation that did not have another more likely explanation. We compared the clinical course of patients with a rickettsial infection who did - and did not - have respiratory involvement.

RESULTS

There were 226 individuals included in the analysis, 51/226 (22 %) had respiratory involvement, including 18/59 (31 %) with QTT and 33/167 (20 %) with scrub typhus, p = 0.09. The imaging findings were heterogenous: 33/51 (65 %) had predominantly alveolar changes, 18/51 (35 %) had interstitial changes and 12/51 (24 %) had a pleural effusion. Those with respiratory involvement were older than individuals without respiratory involvement (median (interquartile range (IQR)) age 51 (37-65) years versus 38 (25-51) years (p = 0.0001). However, most patients (27/51, 53 %) with respiratory involvement had no comorbidity and were younger than 60. Patients with respiratory involvement were more likely to require ICU admission that patients without respiratory involvement (19/51 (38 %) versus 6/175 (3 %) p < 0.001) and 9/51 (18 %) with respiratory involvement required mechanical ventilation. Patients with respiratory involvement were also more likely to require vasopressor support (14/51, 27 % versus 4/175, 2 %, p < 0.001) and renal replacement therapy (4/51, 8 % versus 1/175, 0.6 %, p = 0.01) than patients without respiratory involvement. There were 2/226 (1 %) individuals who died from their rickettsial infection (1 scrub typhus and 1 QTT) during the study period, both had respiratory involvement.

CONCLUSIONS

Respiratory involvement is common in individuals with rickettsial infection in tropical Australia and is associated with a greater risk of life-threatening disease.