Molecular tracking investigation of melioidosis cases reveals regional endemicity in Hainan, China.

Sporadic cases of melioidosis have been reported in Hainan, China for decades; however, to the best of our knowledge, there are no accurate source-identification investigations confirming that melioidosis is endemic. Four indigenous melioidosis cases were identified, which prompted the performance of contact microbiologic and molecular techniques to evaluate endemicity. Environmental samples were collected from various locations surrounding each patient's residence. The samples were screened for Burkholderia pseudomallei (B. pseudomallei) using Ashdown culture medium, and confirmed by polymerase chain reaction and 16S ribosomal DNA sequencing. Clinical and environmental isolates of B. pseudomallei were evaluated by multilocus sequence typing (MLST) and 4-locus multilocus variable number tandem repeat analysis (MLVA-4) for evidence of homology between them. Analysis by MLST indicated that one environmental sample and one clinical colony were sequence type-46, as well as type (8, 3, 11, 9) by MLVA-4. The evidence indicates a likely geographical and epidemiological association. Taken together, B. pseudomallei from the environmental samples in addition to the high molecular homology between the clinical and environmental isolates indicates, at least, regional endemicity of melioidosis in Hainan, China.