Case Definition and Ascertainment

Case Definition

For CDC to consider a case for this surveillance system, the case must meet the following case definition:

  • Group A Streptococcus, group B StreptococcusHaemophilus influenzaeNeisseria meningitidis, or Streptococcus pneumoniae must be isolated from a normally sterile site, such as blood, cerebrospinal fluid, pleural fluid, peritoneal fluid, pericardial fluid, bone, joint/synovial fluid, or internal body site (e.g., lymph node, brain) OR ABCs pathogen-specific nucleic acid must be detected in a specimen obtained from a normally sterile body site, using a validated molecular test
  • Case patient must be a resident of one of the defined surveillance areas

The following is an exception to this sterile site case definition and CDC would count it as a case for this surveillance system:

  • Group A Streptococcus isolated from a wound culture and accompanied by necrotizing fasciitis or streptococcal toxic shock syndrome
  • Autopsy case in which a culture was taken ≤12 hours after death (handled on a case-by-case basis)


Case Ascertainment

ABCs case finding is both active and laboratory-based. Isolation from a normally sterile site is essential to the case definition. Therefore, for case identification, ABCs personnel regularly contact microbiology laboratories in acute care hospitals and reference laboratories processing sterile site specimens for residents of the surveillance area. In hospitals without computerized microbiology data, surveillance personnel call designated microbiology laboratory contacts regularly to identify new cases and request isolate submission. Where microbiology data are computerized, personnel regularly obtain electronic line listings of all ABCs sterile site isolates.