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Scrub typhus has been documented since 1932 in Vietnam, however, the disease burden of scrub typhus remains poorly understood in the country. We conducted this study to describe the phylogenetic analysis of the 56-kDa type-specific antigen (TSA) gene of Orientia tsutsugamushi associated with PCR positive cases of scrub typhus. Of 116 positive samples, 65 type-specific antigen gene sequences were obtained and classified into 3 genogroups: Karp, Kato and Gilliam. The Karp genogroup was the most frequently detected phylogenetic cluster in the study with 30 samples (46%), followed by Kato and Gilliam with 20 (31%) and 15 (23%), respectively. All sequences showed 94-100% nucleotide similarity to reference sequences collected in the central part of Vietnam in 2017. Patients infected with Karp genogroup were more likely to have significant thrombocytopenia than the other genogroups. These results suggest that any scrub typhus vaccine considered for use in Vietnam should provide protection against each of these 3 genogroups., Competing Interests: The authors have declared that no competing interests exist.

Rickettsioses are endemic to Vietnam; however, only a limited number of clinical studies have been performed on these vectorborne bacteria. We conducted a prospective hospital-based study at 2 national referral hospitals in Hanoi to describe the clinical characteristics of scrub typhus and murine typhus in northern Vietnam and to assess the diagnostic applicability of quantitative real-time PCR assays to diagnose rickettsial diseases. We enrolled 302 patients with acute undifferentiated fever and clinically suspected rickettsiosis during March 2015-March 2017. We used a standardized case report form to collect clinical information and laboratory results at the time of admission and during treatment. We confirmed scrub typhus in 103 (34.1%) patients and murine typhus in 12 (3.3%) patients. These results highlight the need for increased emphasis on training for healthcare providers for earlier recognition, prevention, and treatment of rickettsial diseases in Vietnam.