Development and Evaluation of a Dipstick Diagnostic Test for

The emergence ofNeisseria meningitidis serogroup X (NmX) in the African meningitis belt has urged the development of diag-nostic tools and vaccines for this serogroup, especially following the introduction of a conjugate vaccine againstN. meningitidis serogroup A (NmA).We have developed and evaluated a new rapid diagnostic test (RDT) for detecting the capsular polysaccha-ride (cps) antigen of this emerging serogroup.Whole inactivated NmX bacteria were used to immunize rabbits. Following puri-fication by affinity chromatography, the cpsX-specific IgG antibodies were utilized to develop an NmX-specific immunochro-matography dipstick RDT. The test was validated against purified cpsX andmeningococcal 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 105 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 % proba-bility of declaring disease or not when the test is positive or negative, respectively. This unique NmX-specific test could be adde