Comparison of meningococcal disease surveillance systems - United States, 2005-2008.

Meningococcal disease is a nationally notifiable disease caused by the bacterium Neisseria meningitidis. Rates of the disease have decreased since 2000 and are currently at a historic low. The National Notifiable Diseases Surveillance System (NNDSS) and Active Bacterial Core surveillance (ABCs) are the two surveillance systems in the United States that track cases of meningococcal disease. Whereas NNDSS (a passive surveillance system) covers all of the United States and records both probable and confirmed cases of meningococcal disease, ABCs (an active surveillance system) covers six states and portions of four other states and records only culture-confirmed cases. However, ABCs surveillance data are more detailed than NNDSS and are more widely used in vaccine policy and development. To determine whether ABCs estimates of the number of cases of meningococcal disease were far lower than NNDSS counts and the contribution of polymerase chain reaction (PCR) to that difference, CDC conducted an analysis to compare the two systems. CDC compared 1) the number of meningococcal disease cases reported by NNDSS in ABCs areas during 2005-2008 with the number reported by both systems and 2) the mean annual number of cases reported by NNDSS nationally during 2005-2008, with the mean projected national number from ABCs. The results of these two calculations indicated that 8.9% or 14.5% of meningococcal disease cases reported by NNDSS, respectively, were not reported by ABCs, most commonly because they were probable cases detected by PCR testing. Because ABCs data do not substantially underestimate the number of cases of meningococcal disease, implementing PCR testing for N. meningitidis in all ABCs reference laboratories likely would not increase estimates of disease greatly.