This story is not atypical at all. This round worm's life cycle includes
embryonation within hours of the eggs being shed by the fecal route.
Therefore, autoinfection, reinfection and institutional and family clusters
are common. This is unlike whipworms. The eggs of E. vermicularis can
survive for probably up to 2-3 weeks outside the body just waiting to be
picked up on the fingers and put in the mouth. I would treat this child and
his entire family (and daycare if they change diapers or due not use good
hygiene with toddlers) with one dose 100mg of mebendazole. I would then
repeat this in 2 weeks to assure that any reinfection is squelched before
new females are available to lay eggs. The incubation period for the eggs
is about a month so treating at 2 weeks should work well. I would teach
them hygiene. I might have them change the bed linens on day 0 and every 7
days thereafter for 3 weeks. Although this practice is not really proven
necessary, it certainly does not hurt. His potty should be cleaned as well.
There are other drug choices but I believe the failure here is not of the
drug but of the timing and completeness of treatment. This child is likely
just getting reinfected.
My 2 cents worth,
Randy Cordle MD
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