Twin closeness and co-twin risk for substance use disorders: assessing the impact of the equal environment assumption

Studies were conducted from May, 1993 to April, 1995 to determine the changing patterns of infection by the liver fluke, Clonorchis sinensis, among residents and fish hosts in Kyongbuk Province. The infection rate among residents was 7.7% by stool examination. The rate in males (11.3%) was significantly higher than females (4.1%). Positive rate of intradermal test was 27.6% in the same population. The special type of a simple catalytic model was applied for the analysis of intradermal positive reactors by age and sex, and the equation was y = 0.4776 (1 - e-0.0375t) for males and, y = 0.2085 (1 - e-0.0138t) for females. Analysis of stool examination data by two-stage catalytic model revealed y = 0.025 (e-0.00471 - e-0.0235t). The annual Clonorchis infection rate was 4.7 per 1,000 susceptibles and the annual loss rate was 23.5 per 1,000 infected. The frequency distribution by the eggs per gram (EPG) was calculated as well as the cumulative percentages of positives. The regression equations were y = 0.929 + 1.506 log x for males and, y = 0.473 + 1.767 log x for females. Of the 25 fish species, 7 species were infected with Clonorchis metacercariae. Infection rates varied by the species, and ranged from 2.8% in Puntungia herzi to 30.0% in Pseudorasbora parva. Average number of the matacercariae per gram of flesh was 58.1 in P. parva, followed by 10.2 in Gnathopogon atromaculatus, 7.0 in Saurogobio dabryi, and 3.0 in Paracheilognathus rhombea. The present study indicates that clonorchiasis in Kyongbuk Province is less prevalent than that of several decades ago.