Development of the epidemiological situation in invasive meningococcal disease in the Czech Republic caused by emerging Neisseria meningitidis clone ET-15/37.

Meningococcal clone ET-15/37, which appeared as a new one in the Czech Republic in 1993, caused an emergency epidemiological and clinical situation in invasive meningococcal disease, characterized by a high fatality rate (20%) compared to the "normal" fatality rate due to "non ET-15/37" strains. Morbidity rate increased since the first year of the new clone occurrence and reached the peak in 1995. This clone has spread all over the country and investigation of the epidemiological markers of Neisseria meningitidis allowed to quickly recognize the emergency situation and subsequently to provide a targeted vaccination with A + C polysaccharide meningococcal vaccine which prevented the spread of the disease caused by Neisseria meningitidis C. The most frequent phenotype of ET-15/37 clone was C:2a:P1.2(P1.5) and its percentage achieved 80% of group C Neisseria meningitidis strains tested. This antigenic shift of Neisseria meningitidis was associated with the age shift in invasive meningococcal disease morbidity: teenagers started to be the most affected age group and later age group of 1-4 olds followed with high morbidity rates. In 1995 B variant of ET-15/37 clone, B:2a:P1.2(P1.5), appeared, causing a high fatality rate, too. Some data are indicative of a possible decrease in the invasive meningococcal disease incidence in the Czech Republic; nevertheless, the active surveillance and detailed investigation of meningococci have to be continued. After four years following the vaccination and chemoprophylaxis strategy recommended in the Guidelines, set up by the National Reference Laboratory for Meningococcal Infections in 1993, it is possible to conclude, that there have been practically no secondary cases of invasive meningococcal disease in the Czech Republic.