with H552Y substitution on gene shows attenuated behavior : report of a rifampicin-resistant case following chemoprophylaxis.

We present the first Italian reported case of an invasive meningococcal disease with rifampicin-resistance (Rif-R)secondary to chemoprophylaxis. The case is entered in a cluster of two IMDs registered in Tuscany, Italy, in November 2019 caused by two non-differentiable group-C belonging to ST-11 clonal-complex. The contact case, differently from the index, harbored H552Y mutation on gene which is known to confer Rif-R putting a high-cost fee on bacterial fitness. The extremely mild clinical presentation in the contact can constitute an demonstration of the virulence attenuation observed for H552Ymutants. Clinicians should be aware of the possibility of secondary cases with induced Rif-R and keep a high level of suspicion on contacts who received rifampicin-chemoprophylaxis. Molecular characterization of Rif-R should be performed routinely directly on biological samples and not only on isolates, in order to rapidly detect rare cases of resistance and consequently modify chemoprophylaxis for contacts.