Clinical isolates of Streptococcus iniae from Asia are more mucoid and β-hemolytic than those from North America

Streptococcus iniae, a widely distributed fish pathogen, is known to cause rare cases of human infection. We describe 2 cases of invasive S. iniae infection, one with septic arthritis complicating chronic gout and the other with bacteremic cellulitis. Both patients were Chinese and have been regularly handling fresh fish for cooking. Both isolates were unidentified or misidentified by 3 commercially available identification system and were only identified by 16S rRNA gene sequencing. When compared with a clinical isolate of S. iniae from Canada, their colonies were larger, more β-hemolytic, and mucoid. Although bacteremic cellulitis has been described as the most common infection associated with S. iniae, the bacterium has not been reported to cause exacerbations of gouty arthritis previously. Clinical laboratories should be aware of the possibility of different colony morphology of S. iniae from Asia. More accurate identification of nongroupable β-hemolytic streptococci, especially from patients with epidemiologic linkage to fresh fish, may uncover more cases of S. iniae infection. The Asian population and handlers of fresh fish should be informed of the risk of acquiring S. iniae infection.