Diagnostic accuracy of antigen-based immunochromatographic rapid diagnostic tests for the detection of <i>Salmonella</i> in blood culture broth

<div><p>Background</p><p>In low resource settings, <i>Salmonella</i> serovars frequently cause bloodstream infections. This study investigated the diagnostic performance of immunochromatographic rapid diagnostic tests (RDTs), which detect <i>Salmonella</i> antigens, when applied to stored grown blood culture broth.</p><p>Material/Methods</p><p>The SD Bioline One Step <i>Salmonella</i> Typhi Ag Rapid Detection Kit (Standard Diagnostics, Republic of Korea), marketed for the detection of <i>Salmonella enterica</i> serovar Typhi (<i>Salmonella</i> Typhi) in stool and the <i>Salmonella</i> Ag Rapid Test (Creative Diagnostics, USA), marketed for the detection of all <i>Salmonella</i> serotypes in stool, were selected for evaluation based on a pre-test evaluation of six RDT products. The limits of detection (LOD) for culture suspensions were established and the selected RDT products were assessed on 19 freshly grown spiked blood culture broth samples and 413 stored clinical blood culture broth samples, collected in Cambodia and the Democratic Republic of the Congo.</p><p>Results</p><p>The LOD of both products was established as 10⁷−10⁸ CFU/ml. When applied to clinical blood culture broth samples, the diagnostic sensitivity and specificity of the SD Bioline RDT were respectively 100% and 79.7% for the detection of <i>Salmonella</i> Typhi; 94.4% (65/69) of false-positive results were caused by <i>Salmonella</i> Enteritidis. When considering the combined detection of <i>Salmonella</i> Typhi and Enteritidis (both group D <i>Salmonella</i>), sensitivity and specificity were 97.9% and 98.5% respectively. For Creative Diagnostics, diagnostic sensitivity was 78.3% and specificity 91.0% for all <i>Salmonella</i> serotypes combined; 88.3% (53/60) of false negative results were caused by <i>Salmonella</i> Paratyphi A.</p><p>Conclusions</p><p>When applied to grown blood culture broths, the SD Bioline RDT had a good sensitivity and specificity for the detection of <i>Salmonella</i> Typhi and <i>Salmonella</i> Enteritidis. The Creative Diagnostics product had a moderate sensitivity and acceptable specificity for the detection of all <i>Salmonella</i> serovars combined and needs further optimization. A RDT that reliably detects <i>Salmonella</i> Paratyphi A is needed.</p></div

Presence of black and red colored test lines.

<p>Samples applied to both tests (<i>Salmonella</i> Ag Rapid Test, Creative diagnostics) contained <i>Salmonella</i> Enteritidis and both were scored as a positive test result. The test above shows a red colored control line and a black colored test line. The picture below shows a red colored control and test line.</p

Bacterial strains used for spiking blood culture bottles and corresponding rapid diagnostic test results.

<p>Bacterial strains used for spiking blood culture bottles and corresponding rapid diagnostic test results.</p

Determination of limit of detection and corresponding test line intensity for each rapid diagnostic test.

<p>Determination of limit of detection and corresponding test line intensity for each rapid diagnostic test.</p

Variable background clearance.

<p>Both tests shown (Standard Diagnostics Bioline One Step <i>Salmonella</i> Typhi Ag Rapid Detection Kit) with the presence of a control line and absence of a test line, show a negative test result. Background clearance is scored poor for the test above (more reddish) and good for the test below.</p

Characteristics of the <i>Salmonella</i> antigen-based immunochromatographic rapid diagnostic tests evaluated.

<p>Characteristics of the <i>Salmonella</i> antigen-based immunochromatographic rapid diagnostic tests evaluated.</p

Direct atomic scale determination of magnetic ion partition in a room temperature multiferroic material

The five-layer Aurivillius phase Bi6TixFeyMnzO18 system is a rare example of a single-phase room temperature multiferroic material. To optimise its properties and exploit it for future memory storage applications, it is necessary to understand the origin of the room temperature magnetisation. In this work we use high resolution scanning transmission electron microscopy, EDX and EELS to discover how closely-packed Ti/Mn/Fe cations of similar atomic number are arranged, both within the perfect structure and within defect regions. Direct evidence for partitioning of the magnetic cations (Mn and Fe) to the central three of the five perovskite (PK) layers is presented, which reveals a marked preference for Mn to partition to the central layer. We infer this is most probably due to elastic strain energy considerations. The observed increase (>8%) in magnetic cation content at the central PK layers engenders up to a 90% increase in potential ferromagnetic spin alignments in the central layer and this could be significant in terms of creating pathways to the long-range room temperature magnetic order observed in this distinct and intriguing material system

Assessment of labelling and instructions for use of 11 rapid diagnostic tests used in the NIDIAG persistent fever study.

<p>Assessment of labelling and instructions for use of 11 rapid diagnostic tests used in the NIDIAG persistent fever study.</p

Cassettes and buffer bottles from different products but indistinguishable from each other.

<p>Cassettes and buffer bottles from different products but indistinguishable from each other.</p

Characteristics of 11 rapid diagnostic tests used in the NIDIAG persistent fever study.

<p>Characteristics of 11 rapid diagnostic tests used in the NIDIAG persistent fever study.</p