This circular, drafted following consultation with the French High Council for Public Health, is intended to rescind and replace sheets 2, 3, 4, and 5 of Circular DGS/SD5C/No. 542 of March 8, 2001, with the updated forms attached hereto, taking into account, in particular, the polymerase chain reaction (PCR) in the case definition and meningococcal C conjugate vaccines. In particular, it is intended to enable the rapid identification of situations requiring further investigation, which may lead to the implementation of exceptional preventive measures. The opinion of the French High Council for Public Health dated May 16, 2002, regarding the definition of cases of invasive meningococcal infections in individuals for whom prophylaxis should be considered and which must be reported to the health authority, is reproduced in this document. (R.A.)