Prevalence and mean intensity of S. mansoni infection was lower in the snack schools , 1.3 % ( 95 % CI 0.6 % -2.6 % ) and 38.3 eggs per gram of stool ( epg ) ( 95 % CI 21.8-67 .2 ) , compared to that in the non-snack schools , 14.1 % ( 95 % CI 11.6 % -16.9 % ) ( p = 0.001 ) and 78.4 epg ( 95 % CI 60.6-101 .5 ) ( p = 0.001 ) , respectively .