Clinical Features and Risk Factors for Severe Disease of Rickettsiosis: A Military Hospital-Based Study in Bangkok, Thailand

Background: Rickettsiosis is Southeast Asia’s third leading cause of undifferentiated fever. Due to limited epidemiological data and nonspecific symptoms, diagnosing the disease is complex, leading to treatment challenges and complications. Military personnel are at a higher risk for rickettsial exposure, and their treatment might be delayed due to military duties. Objectives: The study aimed to investigate the outbreak, symptoms, and clinical manifestations of rickettsiosis, as well as the risk factors for severe disease, among patients treated at the military hospital in Bangkok, Thailand. Methods: A retrospective analysis of rickettsiosis’s epidemiology, symptoms, and clinical manifestations was performed. The data were collected from patient electronic medical records at Phramongkutklao Hospital from June 2009 to May 2020. Results: Of 184 confirmed patients diagnosed with rickettsial infection, 12 scrub typhus, 16 murine typhus, and 156 were clinically diagnosed with rickettsiosis. Nineteen cases (10%) were grouped as severe rickettsial infection, and the other 165 (90%) were in the non-severe group. Fever, myalgia, rigor, and headache were common presentations of rickettsiosis. Alteration of consciousness and tachypnea were common in those with severe rickettsiosis group. Impaired renal function, elevated bilirubin, elevated alkaline phosphatases, aspartate aminotransferase, and alanine aminotransferase, pyuria, as well as abnormal chest radiographs, were more common findings in the severe rickettsiosis group. Additionally, the rate of ICU admission (73.7% vs. 8.5%, p < 0.001) and duration of hospitalization (18.63 ± 20 vs. 7.42 ± 7.58, p < 0.026) were significantly higher in the severe rickettsiosis group. The mortality rate of rickettsiosis was 2.1%. Elevated bilirubin (OR = 17.93, 95% CI = 3.52-91.42, p = 0.001) and abnormal chest radiograph (OR = 11.73, 95% CI = 1.36-100.89, p = 0.025) were independently predictive for severe disease. Conclusion: Murine typhus was more common in a military hospital in Bangkok and less severe than scrub typhus. Increased bilirubin levels and abnormal chest radiography with bilateral alveolar infiltration tend to predict severe rickettsial infection independently.