IID-1.2 Data Details

FOR SINGLE DATA YEARS: Case rates are calculated based on the resident population of the ABCs surveillance areas for the data year involved. For census years (e.g. 2010), population counts enumerated as of April 1 are used. For all other years, populations estimates as of July 1 are used. Postcensal population estimates are used in rate calculations for years after a census year and match the data year vintage (e.g. July 1, 2011 resident population estimates from Vintage 2011 are used as the denominator for 2011 rates). Postcensal population estimates are used in rate calculations for the years between censuses (e.g. 1991-1999, 2001-2009).

Data reflect cases of Hib disease among children less than 5 years of age submitted to Active Bacterial Core surveillance.

The Active Bacterial Core surveillance (ABCs) system is an active laboratory and population-based surveillance system that provides reports of H. influenzae cases from all or parts of 10 states in the United States. ABCs is supported by the CDC as part of its Emerging Infections Program network. The population under surveillance was 36,748,349 in 2009 (representing 12.0% of the US population).

A case was defined as isolation of H. influenzae from a normally sterile body site (eg, blood or cerebrospinal fluid) in a person aged <5 years. Illness outcome was based on patient status at the time of hospital discharge. Serotyping of H. influenzae was performed by using slide agglutination or polymerase chain reaction. All isolates from ABCs sites were sent to the CDC, where serotype was confirmed by using slide agglutination, Haemophilus quad identification plates or API Neisseria-Haemophilus strips, and polymerase chain reaction. The CDC result was used as the final serotype in the ABCs data set. This measure includes confirmed cases of H. influenzae type b disease.