How Long Can Stool Samples Be Fixed for an Accurate Diagnosis of Soil-Transmitted Helminth Infection Using Mini-FLOTAC?

Beatrice Barda, Marco Albonico, Davide Ianniello, Shaali M. Ame, Jennifer Keiser, Benjamin Speich, Laura Rinaldi, Giuseppe Cringoli, Roberto Burioni, Antonio Montresor, Jürg Utzinger

Research output: Contribution to journalArticle

Abstract

Kato-Katz is a widely used method for the diagnosis of soil-transmitted helminth infection. Fecal samples cannot be preserved, and hence, should be processed on the day of collection and examined under a microscope within 60 min of slide preparation. Mini-FLOTAC is a technique that allows examining fixed fecal samples. We assessed the performance of Mini-FLOTAC using formalin-fixed stool samples compared to Kato-Katz and determined the dynamics of prevalence and intensity estimates of soil-transmitted helminth infection over a 31-day time period. The study was carried out in late 2013 on Pemba Island, Tanzania. Forty-one children were enrolled and stool samples were subjected on the day of collection to a single Kato-Katz thick smear and Mini-FLOTAC examination; 12 aliquots of stool were fixed in 5% formalin and subsequently examined by Mini-FLOTAC up to 31 days after collection. The combined results from Kato-Katz and Mini-FLOTAC revealed that 100% of children were positive for Trichuris trichiura, 85% for Ascaris lumbricoides, and 54% for hookworm. Kato-Katz and Mini-FLOTAC techniques found similar prevalence estimates for A. lumbricoides (85% versus 76%), T. trichiura (98% versus 100%), and hookworm (42% versus 51%). The mean eggs per gram of stool (EPG) according to Kato-Katz and Mini-FLOTAC was 12,075 and 11,679 for A. lumbricoides, 1,074 and 1,592 for T. trichiura, and 255 and 220 for hookworm, respectively. The mean EPG from day 1 to 31 of fixation was stable for A. lumbricoides and T. trichiura, but gradually declined for hookworm, starting at day 15. The findings of our study suggest that for a qualitative diagnosis of soil-transmitted helminth infection, stool samples can be fixed in 5% formalin for at least 30 days. However, for an accurate quantitative diagnosis of hookworm, we suggest a limit of 15 days of preservation. Our results have direct implication for integrating soil-transmitted helminthiasis into transmission assessment surveys for lymphatic filariasis.

Original languageEnglish
Article numbere0003698
JournalPLoS Neglected Tropical Diseases
Volume9
Issue number4
DOIs
Publication statusPublished - Apr 7 2015

ASJC Scopus subject areas

  • Infectious Diseases
  • Public Health, Environmental and Occupational Health
  • Pharmacology, Toxicology and Pharmaceutics(all)

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    Barda, B., Albonico, M., Ianniello, D., Ame, S. M., Keiser, J., Speich, B., Rinaldi, L., Cringoli, G., Burioni, R., Montresor, A., & Utzinger, J. (2015). How Long Can Stool Samples Be Fixed for an Accurate Diagnosis of Soil-Transmitted Helminth Infection Using Mini-FLOTAC? PLoS Neglected Tropical Diseases, 9(4), [e0003698]. https://doi.org/10.1371/journal.pntd.0003698