title: How long can stool samples be fixed for an accurate diagnosis of soil-transmitted helminth infection using Mini-FLOTAC?
abstract: BACKGROUND
  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.
  
  
  METHODS
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Medical Parasitology and Infection Biology, Swiss Tropical and Public Health Institute, Basel, Switzerland; University of Basel, Basel, Switzerland.
authors.forename: Beatrice
authors.initials: B
authors.lastname: Barda
authors.affiliation: Ivo de Carneri Foundation, Milano, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Albonico
authors.affiliation: Section of Veterinary Parasitology and Parasitic Diseases, University of Naples Federico II, Naples, Italy.
authors.forename: Davide
authors.initials: D
authors.lastname: Ianniello
authors.affiliation: Laboratory Division, Public Health Laboratory-Ivo de Carneri, Chake-Chake, Tanzania.
authors.forename: Shaali M
authors.initials: SM
authors.lastname: Ame
authors.affiliation: Department of Medical Parasitology and Infection Biology, Swiss Tropical and Public Health Institute, Basel, Switzerland; University of Basel, Basel, Switzerland.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Keiser
authors.affiliation: Department of Medical Parasitology and Infection Biology, Swiss Tropical and Public Health Institute, Basel, Switzerland; University of Basel, Basel, Switzerland.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Speich
authors.affiliation: Section of Veterinary Parasitology and Parasitic Diseases, University of Naples Federico II, Naples, Italy.
authors.forename: Laura
authors.initials: L
authors.lastname: Rinaldi
authors.affiliation: Section of Veterinary Parasitology and Parasitic Diseases, University of Naples Federico II, Naples, Italy.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Cringoli
authors.affiliation: Laboratory of Microbiology and Virology, San Raffaele Hospital, Milan, Italy.
authors.forename: Roberto
authors.initials: R
authors.lastname: Burioni
authors.affiliation: Department of Control of Neglected Tropical Diseases, World Health Organization, Geneva, Switzerland.
authors.forename: Antonio
authors.initials: A
authors.lastname: Montresor
authors.affiliation: University of Basel, Basel, Switzerland; Department of Epidemiology and Public Health, Swiss Tropical and Public Health Institute, Basel, Switzerland.
authors.forename: Jürg
authors.initials: J
authors.lastname: Utzinger
mesh_terms: D000723:Ancylostomatoidea / Q000302:isolation & purification; D000818:Animals; D017164:Ascaris lumbricoides / Q000302:isolation & purification; D002648:Child; D005243:Feces / Q000469:parasitology*; D005260:Female; D005557:Formaldehyde; D006373:Helminthiasis / Q000175:diagnosis* / Q000453:epidemiology*; D006801:Humans; D007195:Indian Ocean Islands / Q000453:epidemiology; D008297:Male; D008853:Microscopy; D015995:Prevalence; D012680:Sensitivity and Specificity; D012987:Soil / Q000469:parasitology*; D013048:Specimen Handling / Q000379:methods*; D013636:Tanzania / Q000453:epidemiology; D013997:Time Factors; D014258:Trichuris / Q000302:isolation & purification
chemical_list: D012987:Soil; D005557:Formaldehyde
references.citation: Parasit Vectors. 2015;8:82
references.pmid: 25652120
references.citation: Eur J Clin Microbiol Infect Dis. 2014 May;33(5):815-22
references.pmid: 24272064
references.citation: PLoS Negl Trop Dis. 2014 Feb;8(2):e2708
references.pmid: 24551267
references.citation: Trans R Soc Trop Med Hyg. 2009 Apr;103(4):347-54
references.pmid: 19168197
references.citation: East Afr Med J. 1997 May;74(5):294-8
references.pmid: 9337006
references.citation: Am J Trop Med Hyg. 1968 May;17(3):382-91
references.pmid: 5690644
references.citation: Trans R Soc Trop Med Hyg. 2012 Mar;106(3):199-201
references.pmid: 22261186
references.citation: PLoS Negl Trop Dis. 2013;7(8):e2344
references.pmid: 23936577
references.citation: N Engl J Med. 2014 Feb 13;370(7):610-20
references.pmid: 24521107
references.citation: PLoS Negl Trop Dis. 2009;3(1):e366
references.pmid: 19172171
references.citation: Geospat Health. 2013 May;7(2):399-404
references.pmid: 23733301
references.citation: Acta Trop. 2013 Nov;128(2):412-22
references.pmid: 21586268
references.citation: J Vis Exp. 2012;(66):e3966
references.pmid: 22951972
references.citation: Lancet Infect Dis. 2015 Mar;15(3):277-84
references.pmid: 25589326
references.citation: Am J Trop Med Hyg. 2014 Apr;90(4):661-6
references.pmid: 24493672
references.citation: Trans R Soc Trop Med Hyg. 2008 Jan;102(1):84-90
references.pmid: 18028969
references.citation: Rev Inst Med Trop Sao Paulo. 1972 Nov-Dec;14(6):397-400
references.pmid: 4675644
references.citation: Lancet. 2006 May 6;367(9521):1521-32
references.pmid: 16679166
references.citation: Trans R Soc Trop Med Hyg. 2007 Feb;101(2):140-5
references.pmid: 16824566
references.citation: PLoS Negl Trop Dis. 2013;7(6):e2223
references.pmid: 23755308
references.citation: Clin Microbiol Infect. 2010 Mar;16(3):267-73
references.pmid: 19456836
references.citation: Biometrics. 1977 Mar;33(1):159-74
references.pmid: 843571
references.citation: Trans R Soc Trop Med Hyg. 2011 Dec;105(12):683-93
references.pmid: 22040463
references.citation: Nat Protoc. 2010 Mar;5(3):503-15
references.pmid: 20203667
references.citation: Parasit Vectors. 2010 Aug 14;3:71
references.pmid: 20707931
references.citation: Am J Trop Med Hyg. 2015 Feb;92(2):342-53
references.pmid: 25487730
references.citation: World Health Organ Tech Rep Ser. 2002;912:i-vi, 1-57, back cover
references.pmid: 12592987
references.citation: Parasit Vectors. 2014;7:271
references.pmid: 24929554
references.citation: PLoS Negl Trop Dis. 2010;4(7):e754
references.pmid: 20651931
references.citation: Parasit Vectors. 2013;6(1):220
references.pmid: 23902918