Opisthorchis viverrini infection in rural and urban communities in northeast Thailand.

The prevalence and intensity of liver-fluke (Opisthorchis viverrini) infection were investigated among 559 patients who were born in, and had lived all their lives in, either the rural or urban northeastern Thailand. 344 (79.4%) of 433 rural dwellers were infected compared with only 69 (54.8%) of 126 urban dwellers (P less than 0.005). The intensity of infection, and the reported level of consumption of koi-pla, a favourite dish of local inhabitants prepared from uncooked freshwater fish which often contains viable metacercariae, were greater among rural dwellers than their urban counterparts (P less than 0.05 to P less than 0.005). Infection due to O. viverrini appears to be mainly a rural problem strongly associated with the habit and frequency of eating koi-pla.