A new format of the CATT test for the detection of Human African Trypanosomiasis, designed for use in peripheral health facilities

Abstract

Summaryobjectives To test the reproducibility and thermostability of a new format of the Card-Agglutination Test for Trypanosomiasis (CATT) test for Human African Trypanosomiasis (HAT), designed for use at primary health care facility level in endemic countries.methods A population of 4217 from highly endemic villages was screened using the existing format of the CATT test (CATT-R250) on whole blood. All those testing positive (220) and a random sample of negatives (555) were retested in the field with the new format (CATT-D10). Inter-format reproducibility was assessed by calculating kappa. All samples testing positive on whole blood with either method were further evaluated in Belgium by CATT titration of serum by two observers, using both old and new format. CATT-D10 test kits were incubated under four temperature regimens (4, 37, 45°C and fluctuating) with regular assessments of reactivity over 18 months.results Inter-format reproducibility of CATT-D10 vs. CATT-R250 on whole blood performed by laboratory technicians in the field was excellent with kappa values of 0.83-0.89. Both inter-and intra-format reproducibility assessed by CATT titration were excellent, with 96.5-100% of all differences observed falling within the limits of ±1 titration step. After 18 months, reactivity of test kits incubated under all four temperature regimens was still well above the minimum threshold considered acceptable.conclusion The CATT-D10 is thermostable and can be used interchangeably with the old format of the CATT test. It is highly suitable for use in peripheral health facilities in HAT-endemic countries.

Human African Trypanosomiasis Diagnosis in First-Line Health Services of Endemic Countries, a Systematic Review

“…It is a direct agglutination test based on a freeze-dried purified, formaldehyde-fixed and Coomassie-blue-stained bloodstream-form of T. b. gambiense variable antigen type LiTat 1.3. Three CATT formats are available: the classical CATT test on whole blood [5], the CATT on filter paper [12]–[17] and the CATT-D10 [18]. The CATT is a fast and simple agglutination assay for detection of T. b. gambiense -specific antibodies in the blood, plasma, or serum of HAT patients.…”

“…The rotator works on 12 V DC and is usually operated on a car battery; it can also be operated on eight 1.5 V battery cells. Reported sensitivity of CATT on undiluted blood varies from 68·8% to 100% [13], [15]–[17], [19]–[23], reported specificity ranges between 83·5% and 99·3% [13], [15], [17], [19]–[25] and reproducibility is good (Kappa coefficient = 0·84) [18]. The CATT test fulfils each of the ASSURED criteria except robustness since it is not thermostable (table 1).…”

Enhanced passive screening and diagnosis for gambiense human African trypanosomiasis in north-western Uganda – Moving towards elimination

“…Patients with such symptoms and are negative with a malaria test, or are unresponsive to malaria treatment, should be considered potential HAT cases and screened with a serological test for HAT. Until recently, the principal screening test for gHAT was the card agglutination test for trypanosomiasis (CATT), which requires cold storage and electricity, and is packed in multiple doses that are not optimal for screening individual patients [8]. This made it difficult to use the test in rural health facilities.…”

Proteomic Selection of Immunodiagnostic Antigens for Human African Trypanosomiasis and Generation of a Prototype Lateral Flow Immunodiagnostic Device

“…Over the years, the CATT test has been optimised to improve sensitivity, specificity and stability. Such modifications include dilution of the blood samples, the use of multiple trypanosome clones expressing different VSG variants and improvements in thermostability [28], [29], [30], [31]. Despite the usefulness and wide deployment of the CATT test, it has several widely accepted limitations [32], [33], [34], [35].…”