Case Report: Soft tissue infection with Burkholderia thailandensis capsular variant: case report from the Lao PDR

Background: Burkholderia thailandensis is an environmental bacteria closely related to Burkholderia pseudomallei that rarely causes infection in humans. Some environmental isolates have shown to express a capsular polysaccharide known as B. thailandensis capsular variant (BTCV), but human infection has not previously been reported. Although B. thailandednisis has been identified in environmental samples in Laos before, there have not been any human cases reported. Case: A 44-year-old man presented to a district hospital in Laos with a short history of fever and pain in his left foot. Physical examination identified a deep soft-tissue abscess in his left foot and an elevated white blood count. A deep pus sample was taken and melioidosis was suspected from preliminary laboratory tests. The patient was initially started on cloxacillin, ceftriaxone and metronidazole, and was then changed to ceftazidime treatment following local melioidosis treatment guidelines. Laboratory methods: A deep pus sample was sent to Mahosot Hospital microbiology laboratory where a mixed infection was identified including Burkholderia sp. Conventional identification tests and API 20NE were inconclusive, and the B. pseudomallei-specific latex agglutination was positive. The isolate then underwent a Burkholderia species specific PCR which identified the isolate as B. thailandensis. The isolate was sent for sequencing on the Illumina NovaSeq 6000 system and multi-locus sequence typing analysis identified the isolate had the same sequence type (ST696) as B. thailandensis E555, a strain which expresses a B. pseudomallei-like capsular polysaccharide. Conclusion: This is the first report of human infection with B. thailandensis in Laos, and the first report of any human infection with the B. thailandensis capsular variant. Due to the potential for laboratory tests to incorrectly identify this bacteria, staff in endemic areas for B. thailandensis and B. pseudomallei should be aware and ensure that appropriate confirmatory methods are used to differentiate between the species.