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 pneumoniaeor methicillin-resistant Staphylococcus aureus must be isolated from a normally sterile site, such as blood, cerebrospinal fluid (CSF), pleural fluid, peritoneal fluid, pericardial fluid, surgical aspirate, bone, joint 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 of one of the six organisms 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.

Active Bacterial Core surveillance (ABCs)

To determine the incidence and epidemiologic characteristics of invasive disease due to Haemophilus influenzae, Neisseria meningitidis, group A Streptococcus, group B Streptococcus, Streptococcus pneumoniae and methicillin-resistant Staphylococcus aureus in multiple large diverse U.S. populations
To determine molecular epidemiologic patterns and microbiologic characteristics of public health relevance for isolates causing the above invasive infections
To provide an infrastructure for further research, such as special studies aimed at identifying risk factors for disease, post-licensure evaluation

Pathogen-Specific Objectives

Group A Streptococcus (GAS)

To determine the distribution of emm types and the association between specific emm types and disease severity in order to guide vaccine development
To track antimicrobial resistance among invasive GAS isolates
To identify potentially modifiable risk factors for community-acquired GAS infections and to identify potentially preventable nosocomial GAS infections such as postpartum and post-surgical infections

Group B Streptococcus (GBS)

To assess the impact of CDC prevention guidelines issued in 2002 recommending universal prenatal screening
To determine the extent to which continuing cases of early-onset GBS disease are preventable through current prevention strategies
To monitor the impact of intrapartum prophylaxis on resistance and non-GBS neonatal sepsis
To identify serotypes responsible for disease in order to guide vaccine development
To characterize invasive GBS disease epidemiology and trends in other age groups, particularly late-onset neonatal disease and adult disease.

Haemophilus influenzae

Determine the incidence and epidemiologic characteristics of invasive Haemophilus influenzaedisease
Monitor impact of the Haemophilus influenzae type b vaccination program
Detect possible emergence of disease due to non-b Haemophilus influenzae
Determine appropriate verification and validation criteria for serotyping

Neisseria meningitidis

To evaluate effectiveness of meningococcal conjugate vaccines and impact on disease burden and herd immunity
To evaluate the impact of meningococcal conjugate vaccines including changes in molecular epidemiology
To evaluate and validate molecular methods to determine or confirm serologic results
To evaluate trends in molecular subtypes and the emergence of antimicrobial resistance

Streptococcus pneumoniae

To track emerging antimicrobial resistance in pneumococcal isolates
To evaluate the impact of new pneumococcal conjugate vaccines for infants on disease burden and on antimicrobial resistance
To evaluate prevention among the elderly through pneumococcal polysaccharide vaccine use

Methicillin-resistant Staphylococcus aureus (MRSA)

To determine the incidence and epidemiologic characteristics of invasive disease due to MRSA in diverse geographic areas and to categorize as healthcare-associated or community-associated
To determine the molecular epidemiologic patterns and microbiologic characteristics of healthcare-associated and community-associated MRSA