title: Improved sensitivity of the urine CAA lateral-flow assay for diagnosing active Schistosoma infections by using larger sample volumes.
abstract: BACKGROUND
  Accurate determination of Schistosoma infection rates in low endemic regions to examine progress towards interruption of transmission and elimination requires highly sensitive diagnostic tools. An existing lateral flow (LF) based test demonstrating ongoing infections through detection of worm circulating anodic antigen (CAA), was improved for sensitivity through implementation of a protocol allowing increased sample input. Urine is the preferred sample as collection is non-invasive and sample volume is generally not a restriction.
  
  
  METHODS
  Centrifugal filtration devices provided a method to concentrate supernatant of urine samples extracted with trichloroacetic acid (TCA). For field trials a practical sample volume of 2 mL urine allowed detection of CAA down to 0.3 pg/mL. The method was evaluated on a set of urine samples (n = 113) from an S. mansoni endemic region (Kisumu, Kenya) and compared to stool microscopy (Kato Katz, KK). In this analysis true positivity was defined as a sample with either a positive KK or UCAA test.
  
  
  RESULTS
  Implementation of the concentration method increased clinical sensitivity (Sn) from 44 to 98% when moving from the standard 10 μL (UCAA10 assay) to 2000 μL (UCAA2000 assay) urine sample input. Sn for KK varied between 23 and 35% for a duplicate KK (single stool, two slides) to 52% for a six-fold KK (three consecutive day stools, two slides). The UCAA2000 assay indicated 47 positive samples with CAA concentration above 0.3 pg/mL. The six-fold KK detected 25 egg positives; 1 sample with 2 eggs detected in the 6-fold KK was not identified with the UCAA2000 assay.
  
  
  CONCLUSIONS
  Larger sample input increased Sn of the UCAA assay to a level indicating 'true' infection. Only a single 2 mL urine sample is needed, but analysing larger sample volumes could still increase test accuracy. The UCAA2000 test is an appropriate candidate for accurate identification of all infected individuals in low-endemic regions. Assay materials do not require refrigeration and collected urine samples may be stored and transported to central test laboratories without the need to be frozen.
authors.affiliation: Department of Molecular Cell Biology, Leiden University Medical Center, Einthovenweg 20, P.O. Box 9600, 2300 RC, Leiden, the Netherlands. p.corstjens@lumc.nl.
authors.forename: Paul L A M
authors.initials: PL
authors.lastname: Corstjens
authors.affiliation: Institute of Primate Research, National Museums of Kenya, Nairobi, Kenya. nyakundirk@gmail.com.
authors.forename: Ruth K
authors.initials: RK
authors.lastname: Nyakundi
authors.affiliation: Department of Molecular Cell Biology, Leiden University Medical Center, Einthovenweg 20, P.O. Box 9600, 2300 RC, Leiden, the Netherlands. C.J.de_Dood@lumc.nl.
authors.forename: Claudia J
authors.initials: CJ
authors.lastname: de Dood
authors.affiliation: Institute of Primate Research, National Museums of Kenya, Nairobi, Kenya. tkariuki@africaonline.co.ke.
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Kariuki
authors.affiliation: Center for Global Health Research, Kenya Medical Research Institute, Kisumu, Kenya. EAkinyi@kemricdc.org.
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Ochola
authors.affiliation: Center for Global Health Research, Kenya Medical Research Institute, Kisumu, Kenya. DKaranja@kemricdc.org.
authors.forename: Diana M S
authors.initials: DM
authors.lastname: Karanja
authors.affiliation: Center for Global Health Research, Kenya Medical Research Institute, Kisumu, Kenya. PMwinzi@kemricdc.org.
authors.forename: Pauline N M
authors.initials: PN
authors.lastname: Mwinzi
authors.affiliation: Department of Parasitology, Leiden University Medical Center, Leiden, the Netherlands. G.J.van_Dam@lumc.nl.
authors.forename: Govert J
authors.initials: GJ
authors.lastname: van Dam
mesh_terms: D000818:Animals; D000947:Antigens, Helminth / Q000652:urine*; D005243:Feces / Q000469:parasitology; D006023:Glycoproteins / Q000652:urine*; D015801:Helminth Proteins / Q000652:urine*; D006801:Humans; D010270:Parasite Egg Count; D012550:Schistosoma mansoni / Q000378:metabolism*; D012555:Schistosomiasis mansoni / Q000175:diagnosis* / Q000652:urine*; D012680:Sensitivity and Specificity
chemical_list: D000947:Antigens, Helminth; D006023:Glycoproteins; D015801:Helminth Proteins; C090907:circulating anodic antigen, Schistosoma mansoni