Abstract
Rapid diagnostics can be accurate but, often, those based on antibody detection for infectious diseases are unwittingly underrated for various reasons. Herein, we described the development of a combined rapid test for two clinically-indistinguishable bacterial diseases, typhoid and paratyphoid A fever, the latter fast emerging as a global threat. By using monoclonal antibodies (mAbs) to bacterial antigens of known chemical structures as probes, we were able to dissect the antibody response in patients at the level of monosaccharides. Thus, a mAb specific for a common lipopolysaccharide antigen (O12) found in both the causative organisms was employed to semi-quantify the amounts of anti-O12 antibodies present in both types of patients in an epitope-inhibition particle-based (TUBEX) immunoassay. This colorimetric assay detected not only anti-O12 antibodies that were abundantly produced, but also, by steric hindrance, antibodies to an adjoining epitope (O9 or O2 in the typhoid or paratyphoid bacillus, respectively). Sensitivity and, particularly, reaction intensities, were significantly better than those obtained using an anti-O9 or anti-O2 mAb-probe in the examination of paired sera from 22 culture-confirmed typhoid patients (sensitivity, 81.8% vs 75.0%) or single sera from 36 culture-confirmed paratyphoid patients (52.8% vs 28.6), respectively. Importantly, sensitivity was better (97.1% for typhoid, 75.0% for paratyphoid) if allowance was made for the absence of relevant antibodies in certain specimens as determined by an independent, objective assay (ELISA) — such specimens might have been storage-denatured (especially the older paratyphoid samples) or procured from non-responders. Benchmarking against ELISA, which revealed high concordance between the two tests, was useful and more appropriate than comparing with culture methods as traditionally done, since antibody tests and culture target slightly different stages of these diseases. Paired sera analysis was insightful, revealing 64% of typhoid patients who had no change in antibody titer over 4–16 days, and 14% with no IgM-IgG class-switching.
Highlights
IntroductionSensitivity and specificity characterize how clinically useful an immunodiagnostic (serological) test is
Sensitivity and specificity characterize how clinically useful an immunodiagnostic test is
We prepared blue latex particles coupled with the anti-O12 monoclonal antibodies (mAbs) (P4E8) and examined the performance of these as substitute indicator particles in various TUBEX tests
Summary
Sensitivity and specificity characterize how clinically useful an immunodiagnostic (serological) test is. These parameters are usually computed by comparing the results obtained from such a test with those derived by culture of the infectious agent from the study cohort This time-honored use of culture as the gold standard in diagnosis has seldom been questioned even though in many situations, culturing is neither sensitive nor practicable [1,2,3]. This raises the possibility that, in some cases, the real worth of immunodiagnostic tests could be unfairly benchmarked. Study of both diseases together allows assay sensitivity and specificity to be addressed more comprehensively, while the availability of detailed information regarding both of the infecting organisms, including, in particular, the relevant antigens, permits high-resolution analysis of specificity
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have