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Methodology - Case Definition and Ascertainment

Case Definition

To be considered a case for this surveillance system, the following case definition must be met:

  • Group A Streptococcus, group B Streptococcus, Haemophilus influenzae, Neisseria meningitidis, Streptococcus pneumoniae or methicillin-resistant Staphylococcus aureus (MRSA) must be isolated from a normally sterile site, such as blood, cerebrospinal fluid (CSF), pleural fluid, peritoneal fluid, pericardial fluid, bone, joint/synovial fluid, or internal body site (e.g., lymph node, brain)
  • Case patient must be a resident of one of the defined surveillance areas

The following are exceptions to this sterile site case definition and would be counted as cases for this surveillance system:

  • Group B Streptococcus isolated from the placenta and/or amniotic fluid with fetal demise
  • Group A Streptococcus isolated from a wound culture and accompanied by necrotizing fasciitis or streptococcal toxic shock syndrome (STSS)

Case Ascertainment

ABCs case finding is both active and laboratory-based. Since isolation from a normally sterile site is essential to the case definition, microbiology laboratories in acute care hospitals and reference laboratories processing sterile site specimens for residents of the surveillance area are contacted regularly for case identification. 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, electronic line listings of all ABCs sterile site isolates are obtained on a monthly basis.

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