Clostridium perfringens is an important pathogen that is responsible for gastroenteritis; the causative agent for the symptoms is C. perfringens enterotoxin (CPE), which is mainly produced by type F C. perfringens . Since shellfishes may gather C. perfringens in the water environment, this study estimated the potential circulation of type F C. perfringens among humans, sewage, and Ruditapes philippinarum (asari clams) as a result of sewage pollution. A comparison of the characteristics among the isolates from 86 sewage influents, 36 effluents, 76 asari clams, and 37 humans was conducted. Serotyping, cpe genotyping, and toxin genotyping showed that C . perfringens with a plasmid IS 1151 sequence downstream of cpe was predominant among sewage influents, effluents, humans, and asari clams. Multilocus sequence typing suggested that some isolates from a human, sewage influents, effluents, and asari clams were linked to each other. These results demonstrated that asari clams are the necessary infection sources of C. perfringens responsible for carriers and foodborne diseases, and that these pathogens from humans infected by asari clams can pollute the water environment. It is useful to assess bacteria such as C. perfringens isolates from sewage to estimate the trend of those from the community.