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Development and evaluation of a dipstick diagnostic test for Neisseria meningitidis serogroup X
Alain Agnememel1, François Traincard2, Sylvie Dartevelle2
1Institut Pasteur, Invasive Bacterial Infection Unit, National Reference Centre for Meningococci, Paris, France WHO Collaborating Centre for Meningococci, Institut Pasteur, Paris, France Université Denis Diderot, Sorbonne Paris Cité, Paris, France.
Abstract:
The emergence of Neisseria meningitidis serogroup X (NmX) in the African meningitis belt has urged the development of diagnostic tools and vaccines for this serogroup, especially following the introduction of a conjugate vaccine against N. meningitidis serogroup A (NmA). We have developed and evaluated a new rapid diagnostic test (RDT) for detecting the capsular polysaccharide (cps) antigen of this emerging serogroup. Whole inactivated NmX bacteria were used to immunize rabbits. Following purification by affinity chromatography, the cpsX-specific IgG antibodies were utilized to develop an NmX-specific immunochromatography dipstick RDT. The test was validated against purified cpsX and meningococcal strains of different serogroups. Its performance was evaluated against that of PCR on a collection of 369 cerebrospinal fluid (CSF) samples obtained from patients living in countries within the meningitis belt (Cameroon, Côte d'Ivoire, and Niger) or in France. The RDT was highly specific for NmX strains. Cutoffs of 10(5) CFU/ml and 1 ng/ml were observed for the reference NmX strain and purified cpsX, respectively. Sensitivity and specificity were 100% and 94%, respectively. A high agreement between PCR and RDT (Kappa coefficient, 0.98) was observed. The RDT gave a high positive likelihood ratio and a low negative likelihood (0.07), indicating almost 100% probability of declaring disease or not when the test is positive or negative, respectively. This unique NmX-specific test could be added to the available set of RDT for the detection of meningococcal meningitis in Africa as a major tool to reinforce epidemiological surveillance after the introduction of the NmA conjugate vaccine.
Insights
A new rapid diagnostic test (RDT) accurately detects Neisseria meningitidis serogroup X (NmX) capsular polysaccharide antigen. This NmX RDT enhances meningitis surveillance in Africa, complementing existing NmA vaccines.
Area of Science:
- Microbiology
- Immunology
- Epidemiology
Background:
- Neisseria meningitidis serogroup X (NmX) is an emerging pathogen in Africa's meningitis belt.
- The introduction of a serogroup A (NmA) conjugate vaccine necessitates surveillance for other serogroups like NmX.
- Development of specific diagnostic tools for NmX is crucial for effective meningitis control.
Purpose of the Study:
- To develop and evaluate a novel rapid diagnostic test (RDT) for the detection of Neisseria meningitidis serogroup X (NmX).
- To assess the performance of the NmX RDT against established methods like PCR using clinical samples.
Main Methods:
- Production of NmX-specific IgG antibodies by immunizing rabbits with whole inactivated NmX bacteria.
- Development of an immunochromatography dipstick RDT using purified cpsX-specific antibodies.
- Validation against purified antigen and various meningococcal strains, followed by performance evaluation on 369 cerebrospinal fluid (CSF) samples.
Main Results:
- The NmX RDT demonstrated high specificity for NmX strains.
- Sensitivity and specificity were 100% and 94%, respectively, with high agreement with PCR (Kappa coefficient, 0.98).
- The test showed a high positive likelihood ratio and a low negative likelihood ratio, indicating reliable diagnostic accuracy.
Conclusions:
- The developed NmX-specific RDT is a unique and effective tool for detecting NmX antigen.
- This RDT can significantly enhance epidemiological surveillance of meningococcal meningitis in Africa.
- It serves as a valuable addition to existing diagnostic capabilities, particularly post-NmA vaccine introduction.
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