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

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)

SerologySample B

ST-specific IgM lateral flow assay (IgMFA)

Investigations on Admission

Routine investigationsBlood Count + Film

Liver and Renal FunctionC-Reactive Protein

SerologySample A

ST-specific IgM lateral flow assay (IgMFA)

Microbiology

Blood Culture(minimum 2ml)

Nucleic Acid Amplification Tests (NAATs)

Polymerase Chain Reaction16-S Ribosomal Amplification

Laboratory Evidence of TF (I34 Patients)

Confirmed

Suspected

Possible

Non-TF

18 Suspected TF patients

IgMFA positive only

NAAT positive only

Positive on both NAAT and IgMFA

IgMFA Sample A Day of Fever (Sample A)

IgMFA Sample B Day of Fever(Sample B)

NAATPolymerase

Chain Reaction(PCR)

NAAT16S Ribosomal Amplification

(16SRA)- 7 1+ 10 - -- 1 1+ 6 - -- 7 1+ 10 - -

1+ 2 2+ 5 - -1+ 3 2+ 6 - -1+ 5 2+ 10 - -4+ 12 4+ 14 - -1+ 4 1+ 7 - +3+ 10 3+ 12 - -1+ 2 1+ 5 - -3+ 6 3+ 10 - -- 3 - 5 + -- 6 1+ 8 - -- 3 - 6 + -

3+ 7 3+ 10 - -1+ 4 1+ 7 - -1+ 5 2+ 7 - -1+ 4 2+ 8 - -

Confirmed Case Serovar NAAT(16SRA or

PCR)

IgMFA(Sample A)

Day of Fever(A)

IgMFA(Sample B)

Day of Fever (B)

1 Typhi - 2+ 6 3+ 10

2 Typhi - 3+ 6 4+ 10

3 Typhi - 2+ 3 3+ 10

4 Typhi + (PCR)

3+ 7 3+ 10

5 Typhi - 4+ 8 4+ 10

•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.