title: Detecting and enumerating soil-transmitted helminth eggs in soil: New method development and results from field testing in Kenya and Bangladesh.
abstract: Globally, about 1.5 billion people are infected with at least one species of soil-transmitted helminth (STH). Soil is a critical environmental reservoir of STH, yet there is no standard method for detecting STH eggs in soil. We developed a field method for enumerating STH eggs in soil and tested the method in Bangladesh and Kenya. The US Environmental Protection Agency (EPA) method for enumerating Ascaris eggs in biosolids was modified through a series of recovery efficiency experiments; we seeded soil samples with a known number of Ascaris suum eggs and assessed the effect of protocol modifications on egg recovery. We found the use of 1% 7X as a surfactant compared to 0.1% Tween 80 significantly improved recovery efficiency (two-sided t-test, t = 5.03, p = 0.007) while other protocol modifications-including different agitation and flotation methods-did not have a significant impact. Soil texture affected the egg recovery efficiency; sandy samples resulted in higher recovery compared to loamy samples processed using the same method (two-sided t-test, t = 2.56, p = 0.083). We documented a recovery efficiency of 73% for the final improved method using loamy soil in the lab. To field test the improved method, we processed soil samples from 100 households in Bangladesh and 100 households in Kenya from June to November 2015. The prevalence of any STH (Ascaris, Trichuris or hookworm) egg in soil was 78% in Bangladesh and 37% in Kenya. The median concentration of STH eggs in soil in positive samples was 0.59 eggs/g dry soil in Bangladesh and 0.15 eggs/g dry soil in Kenya. The prevalence of STH eggs in soil was significantly higher in Bangladesh than Kenya (chi-square, χ2 = 34.39, p < 0.001) as was the concentration (Mann-Whitney, z = 7.10, p < 0.001). This new method allows for detecting STH eggs in soil in low-resource settings and could be used for standardizing soil STH detection globally.
authors.affiliation: Civil and Environmental Engineering, Stanford University, Stanford, California, United States of America.
authors.forename: Lauren
authors.identifier: http://orcid.org/0000-0003-1710-2639
authors.initials: L
authors.lastname: Steinbaum
authors.affiliation: Civil and Environmental Engineering, Stanford University, Stanford, California, United States of America.
authors.forename: Laura H
authors.initials: LH
authors.lastname: Kwong
authors.affiliation: School of Public Health, University of California, Berkeley, Berkeley, California, United States of America.
authors.forename: Ayse
authors.initials: A
authors.lastname: Ercumen
authors.affiliation: Integrative Biology, University of California, Berkeley, Berkeley, California, United States of America.
authors.forename: Makeda S
authors.initials: MS
authors.lastname: Negash
authors.affiliation: School of Public Health, University of California, Berkeley, Berkeley, California, United States of America.
authors.forename: Amira J
authors.initials: AJ
authors.lastname: Lovely
authors.affiliation: Eastern and Southern Africa Center of International Parasite Control, Kenya Medical Research Institute (KEMRI), Nairobi, Kenya.
authors.forename: Sammy M
authors.initials: SM
authors.lastname: Njenga
authors.affiliation: Civil and Environmental Engineering, Stanford University, Stanford, California, United States of America.
authors.forename: Alexandria B
authors.initials: AB
authors.lastname: Boehm
authors.affiliation: Civil and Environmental Engineering, Stanford University, Stanford, California, United States of America.
authors.forename: Amy J
authors.initials: AJ
authors.lastname: Pickering
authors.affiliation: Civil and Environmental Engineering, University of California, Berkeley, Berkeley, California, United States of America.
authors.forename: Kara L
authors.initials: KL
authors.lastname: Nelson
mesh_terms: D000723:Ancylostomatoidea / Q000302:isolation & purification*; D000818:Animals; D001196:Ascariasis / Q000453:epidemiology / Q000469:parasitology; D001200:Ascaris / Q000302:isolation & purification*; D001459:Bangladesh / Q000453:epidemiology; D006725:Hookworm Infections / Q000453:epidemiology / Q000469:parasitology; D006801:Humans; D007630:Kenya / Q000453:epidemiology; D008853:Microscopy; D010270:Parasite Egg Count; D015995:Prevalence; D012987:Soil / Q000469:parasitology*; D014257:Trichuriasis / Q000453:epidemiology / Q000469:parasitology; D014258:Trichuris / Q000302:isolation & purification*
chemical_list: D012987:Soil