The growth of Vibrio vulnificus and the habitat of infected patients in Kumamoto.

In Japan, Vibrio vulnificus (V. vulnificus) infection is very rare, and most infections have occurred in Kumamoto Prefecture (1), and especially around the Ariake and Yatsushiro seas. To investigate the relationship between the occurrence of V. vulnificus infection and environmental factors, including the salinity of seawater and the amount of rain in the Ariake and Yatsushiro seas, we measured the most probable number (MPN) of V. vulnificus in seawater and sea mud. In the Ariake Sea, we also observed the temperature and salinity of seawater at one site located on an estuary where the salinity is easily affected by river water and another site located offshore where seawater is little affected by river water. Furthermore, we investigated the MPN of V. vulnificus and observed the temperature and the salinity of seawater in 25 sites in the Ariake and Yatsushiro seas from July to August 2003 and 2004. In addition, we collected data on patients with V. vulnificus infections in Kumamoto from 1990 to 2006. The MPN of V. vulnificus differed by sampling site. More V. vulnificus were detected around the inland sea than the open sea, and the increase in V. vulnificus levels was affected by rainfall around inland sea areas with many rivers. V. vulnificus increases significantly in brackish water areas, and the salinity of seawater was as important as the seawater temperature. In other words, an area's topography and amount of rain are believed to be important factors for the occurrence of V. vulnificus infection. V. vulnificus infection has been regarded as an infection of hot districts. However, the salinity of seawater may be more important than temperature for the growth of V. vulnificus. Therefore, investigating these geographical and meteorological factors can help predict areas with a higher number of V. vulnificus infection outbreaks.