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An IgM Flow Assay ( IgMFA ) as a Rapid Diagnostic Test (RDT) for

An IgM Flow Assay ( IgMFA ) as a Rapid Diagnostic Test (RDT) for Typhoid (enteric) Fever in Cambodian children. Investigations on Admission. L. Wijedoru 1 , V. Kumar 2 , N. Chanpheaktra 2 , K. Chheng 2 , H. Smits 3 , R. Pastoor 3 ,

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An IgM Flow Assay ( IgMFA ) as a Rapid Diagnostic Test (RDT) for

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  1. An IgM Flow Assay (IgMFA) as a Rapid Diagnostic Test (RDT) for Typhoid (enteric) Fever in Cambodian children Investigations on Admission L. Wijedoru1, V. Kumar2, N. Chanpheaktra2,K. Chheng2, H. Smits3, R. Pastoor3, S. Baker4, S. Peacock5, V. Wuthiekanun5, H. Putchhat6, C. Parry7 1Child and Reproductive Health Group, Liverpool School of Tropical Medicine (LSTM), UK, 2Paediatrics, Angkor Hospital for Children (AHC), Siem Reap, Cambodia, 3Rapid Diagnostics, Royal Tropical Institute (KIT), Amsterdam, The Netherlands, 4Microbiology, Oxford University Clinical Research Unit (OUCRU), Ho Chi Minh City, Vietnam, 5Microbiology, Mahidol Oxford Tropical Medicine Unit (MORU), Bangkok, Thailand 6Laboratory Services, Angkor Hospital for Children, Siem Reap, Cambodia, 7School of Infection and Host Defence, University of Liverpool, UK On Discharge or on Day 10 of fever (whichever was the earlier) • What is known on the topic • Differentiating bacterial infections that require antibiotics, from common viral and parasitic causes in febrile children is often difficult in low-resource settings (LRS) (Maitland, 2010). • Angkor Hospital for Children (AHC) serves a rural population of northern Cambodia at risk of febrile illnesses including malaria, dengue, rickettsiosis, leptospirosis, and melioidosis. • Typhoid (enteric) fever (TF) is a disease caused by Salmonella Typhi (ST) affecting an estimated 13 million people annually in Asia, of which a large proportion are children (Bhutta, 2008). • Blood culture sensitivity in diagnosing TF is only 40-60%, despite being the current gold standard. TF is often diagnosed clinically. • Rapid diagnostic tests (RDTs) can lead to timely and appropriate treatment, and rational prescription of drugs such as antibiotics. • An IgMFA developed by the Royal Tropical Institute (Netherlands) has shown to correspond with clinical pictures of TF in Indonesia despite negative blood cultures (Pastoor et al., 2008). • Objective • To estimate the proportion of febrile children admitted to AHC that have TF. • Methods • Cross-sectional descriptive study between April and June 2009. • All children (< 16 years) admitted to either the in-patient department (IPD) or intensive care unit (ICU) with a history of fever, and a documented temperature of ≥38⁰C within the first 48 hours of admission, were eligible. • Clinical data (history and examination) was collected. • ST-specific NAATs (PCR and 16S-RA) + blood culture were performed on admission. • 5 microlitres of patient serum (from venous blood) was mixed with 130 microlitres of manufacturer buffer solution on admission (Sample A). • A second serum sample was obtained on discharge or on Day 10 of fever (Sample B). • IgMFA results were classed as: negative, +1, +2, or +3 (as per manufacturer). Serology Sample B ST-specific IgM lateral flow assay (IgMFA) Routine investigations Blood Count + Film Liver and Renal Function C-Reactive Protein Microbiology Blood Culture (minimum 2ml) Nucleic Acid Amplification Tests (NAATs) Polymerase Chain Reaction 16-S Ribosomal Amplification Serology Sample A ST-specific IgM lateral flow assay (IgMFA) What this study adds The IgMFA RDT appears more sensitive than blood culture and nucleic acid amplification tests (NAATs). ST-specific IgM responses appear less affected by the factors contributing to low blood culture sensitivity in children, such as culture volume, pre-treatment with antibiotics, and laboratory quality. Results – Disease Burden • Five (3.7%) were confirmed typhoid cases (ST isolated from blood), • Eighteen (13.4%) were suspected cases (positive admission and/or discharge IgM serology and/or positive NAATs) • Eight (6.6%) were possible cases (appropriate clinical picture but all negative tests). • Twelve out of the twenty-one IgMFA positive patients (57.1%) had a rise in IgM titre, strongly suggestive of acute TF seroconversion. • Only four patients in total were positive by NAAT. Two of these were IgMFA positive. Results – Diagnostic Tests Eighteen Suspected (blood culture-negative) cases Five Confirmed (blood culture-positive) cases Conclusions One in six (17.1%) of febrile children admitted to AHC had confirmed or suspected TF. All confirmed cases were positive on IgMFA. IgMFA positivity exceeded that of both blood culture and NAATs. The value of NAATs for the detection of ST in blood appears limited. Further evaluation of the assay's specificity is needed among unselected febrile patients in TF endemic areas. References Bhutta, Z A . 2008. Typhoid fever in the developing world: a neglected disease? ActaTropica. 90(2):211-214 Maitland, K. 2010. Antimicrobials in children admitted to hospital in malaria-endemic areas. British Medical Journal. 340:c1818 Pastoor, R et al 2008. Simple, rapid, and affordable point-of-care test for the serodiagnosis of typhoid fever. Diagnostic Microbiology and Infectious Disease. 61(2): 129-134

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