INVASIVE INFECTIONS DUE TO A FISH PATHOGEN, STREPTOCOCCUS-INIAE

Background Streptococcus iniae is a pathogen in fish, capable of causi ng invasive disease and outbreaks in aquaculture farms. During the win ter of 1995-1996 in the greater Toronto area there was a cluster of fo ur cases of invasive S. iniae infection in people who had recently han dled fresh, whole fish from such farms. Methods We conducted a prospec tive and retrospective community-based surveillance for cases of S. in iae infection in humans. To obtain a large sample of isolates, we stud ied cultures obtained from the surface of fish from aquaculture farms. Additional isolates were obtained from the brains of infected tilapia (oreochromis species). All the isolates were characterized by pulsed- field gel electrophoresis (PFGE). Results During one year, our surveil lance identified a total of nine patients with invasive S. iniae infec tion (cellulitis of the hand in eight and endocarditis in one). All th e patients had handled live or freshly killed fish, and eight had perc utaneous injuries. Six of the nine fish were tilapia, which are common ly used in Asian cooking. Thirteen additional S. iniae isolates (2 fro m humans and 11 from infected tilapia) were obtained from normally ste rile sites. The isolates from the nine patients were indistinguishable by PFGE and were highly related to the other clinical isolates. There was substantial genetic diversity among the 42 surveillance isolates from the surface of fish, but in 10 isolates the PFGE patterns were id entical to those from the patients with S. iniae infection. Conclusion s S. iniae can produce invasive infection after skin injuries during t he handling of fresh fish grown by aquaculture. We identified a clone of S. iniae that causes invasive disease in both humans and fish. (C) 1997, Massachusetts Medical Society.