Patterns of infection, incidence and reinfection with Schistosoma mansoni in Nile Delta Governorate: Kafr El Sheikh.

Abstract

Two annual follow-up measures of incidence, reinfection after treatment and reversion rates were estimated in a large prospective study of Schistosoma mansoni located in the northern Nile Delta of Kafr El Sheikh. Rates were estimated in a cohort established from a probability sample of the entire rural area of Kafr El Sheikh. Infection was determined by the examination of two Kato stool slides. The weighted first and second annual overall incidence rates were 20.4%, SE +/- 1.4 and 15.9%, SE +/- 1.4, respectively. Geometric mean egg counts in incident cases were 35.6 epg, SE +/- 1.2 and 31.0, SE +/- 1.6 in the first and second follow-ups. Incidence was strongly associated with first round prevalence (r2 = 0.34). Reinfection rates were higher: 33.4%, SE +/- 3.1 and 31.0%, SE +/- 2.1. Reinfection was associated with incidence (r2 = 0.32). Reversion rates were highest in children 0 to 4 years old (61.2%, SE +/- 18.1 and 78.5%, SE +/- 7.0, respectively) and increased from the first to second follow-up: 37.2%, SE +/- 3.4 and 47.0%, SE +/- 3.7, respectively. Patterns of these rates by village community, age and sex are also given over both follow-up examinations and comparison with limited data on rates of S. mansoni infection from previous studies, suggests a stable pattern of transmission over time in the Nile Delta.