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Risk Factors Associated with Life-threatening Rickettsial Infections

We retrospectively analyzed 92 cases of severe rickettsial infections in patients (median age = 49 years, 57% male, 37.0% with scrub typhus) in Hong Kong. Immunofluorescence assay was used for diagnostic confirmation. Identification of 1 diagnostic sign (exposure history, rash, or eschar) was possible in 94.6% of the cases. Multivariate analysis suggested that pulmonary infiltrates (odds ratio [OR] = 25.2, 95% confidence interval [CI] = 3.9–160.9, P = 0.001) and leukocytosis (OR = 1.3, 95% CI = 1.0–1.5 per unit increase, P = 0.033) were independent predictors of admission to an intensive care unit (14.1%). Delayed administration of doxycycline was independently associated with major organ dysfunction (23.9%; oxygen desaturation, renal failure, severe jaundice, encephalopathy, cardiac failure) (OR = 1.2, 95% CI = 1.0–1.5 per day delay, P = 0.046; adjusted for age and rickettsia biogroup) and prolonged hospitalization > 10 days (25%) (OR = 1.4, 95% CI = 1.1–1.9 per day delay, P = 0.014). Treatment with fluoroquinolone/clarithromycin did not correlate with clinical outcomes (P > 0.05). Early empirical doxycycline therapy should be considered if clinico-epidemiologic signs of rickettsial infections are present.

Received November 1, 2007. Accepted for publication February 15, 2008.

^* Address correspondence to Nelson Lee, Department of Medicine and Therapeutics, Prince of Wales Hospital, The Chinese University of Hong Kong, Hong Kong, Special Administrative Region, People’s Republic of China. E-mail: leelsn{at}cuhk.edu.hk

Authors’ addresses: Nelson Lee, Bonnie Wong, Grace Lui, Kin Wing Choi, Jenny Ho, Yin Yan Chan, and Clive S. Cockram, Department of Medicine and Therapeutics, Prince of Wales Hospital, 9/F Clinical Science Building, The Chinese University of Hong Kong, Hong Kong, Special Administrative Region, People’s Republic of China, E-mail: leelsn{at}cuhk.edu.hk. Margaret Ip and Rebecca Lam, Department of Microbiology, Prince of Wales Hospital, The Chinese University of Hong Kong; Hong Kong, Special Administrative Region, People’s Republic of China. Owen Tak Yin Tsang, Jak Yiu Lai, and Sik To Lai, Department of Medicine and Geriatrics, Princess Margaret Hospital, Hong Kong, Special Administrative Region, People’s Republic of China. Tak Keung Ng, Department of Pathology, Princess Margaret Hospital, Hong Kong, Special Administrative Region, People’s Republic of China.