Epidemiological studies on the reinfection pattern of Ascaris lumbricoides were undertaken by means of blanket mass chemotherapy and worm collection in a rural village in Korea, during 1977~1980. The study objectives were to determine the age(sex)-specific reinfection rate during 2, 4, 6 and 12 months through repeated mass chemotherapy with pyrantel pamoate, and to observe the familial aggregation tendency of the reinfected cases.
The results obtained are as follows:
1. The age(sex)-reinfection curve revealed that the reinfection rate is much higher in younger individuals than in olders in all of 4 kinds of interval chemotherapy groups. The highest reinfection rate and the highest burden of reinfected worms were observed in preschool childen, followed by primary school students. Such fluctuation in the age-specific reinfection rates was more pronounced in males than in females.
2. There was noted a significant tendency of familial aggregation among the reinfected cases. It is suggested that reinfection occurs never randomly but preferably to the members of certain household families.
From these reinfection analyses, it is inferred that the principal mode of A. lumbricoides transmission in the surveyed rural area is likely to be of 'dooryard type', in which case childen and certain family members are more preferably reinfected. It is also suggested that the preschool childen should be included in the primary targets of mass control programme.
Fig. 1 Age-specific reinfection rate of A. lumbricoides according to masstreatment interval groups.
Fig. 2 Age-specific reinfection rate of A. lumbricoides in male and female villagers.
Fig. 3 Observed and theoretical number of households with 'n' reinfected members.
Table 1 The scheme of repeated mass chemotherapy to 11 hamlets of Hwasong-gun, Korea (1977-'80)
Table 2 Age-specific reinfection rates of A. lumbricoides during mass chemotherapeutic control trials (1977~'80)
Table 3 Overall age-specific reinfection rates of A. lumbricoides in male and female inhabitants (1977~'80)
Table 4 Worm burden of reinfected A. lumbricoides according to age and sex of the inhabitants (1977~'80)
Table 5 The observed (expected) number of households according to number of total family members and reinfected members with A. lumbricoides
Table 6 The *result of statistical test for familial aggregation of A. lumbricoides reinfection
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