ARCHIVED - 5.0 Definitions
5.1 National case definition
In Canada, confirmed cases of invasive GAS disease are notifiable at the national level. Probable cases of invasive GAS disease are not nationally notifiable (Table 1).
Table 1: National Case Definition for Invasive GAS Disease(21)
|Confirmed case||Laboratory confirmation of infection with or without clinical evidence of invasive disease.* Laboratory confirmation requires the isolation of group A streptococcus (Streptococcus pyogenes) from a normally sterile site.|
|Probable case||Invasive disease* in the absence of another identified etiology and with isolation of GAS from a non-sterile site.|
*Clinical evidence of invasive disease may be manifested as several conditions. These include:
a) STSS, which is characterized by hypotension (systolic blood pressure ≤ 90 mmHg in adults or < 5th percentile for age in children) and at least two of the following signs:
b) soft-tissue necrosis, including necrotizing fasciitis, myositis or gangrene;
c) meningitis; or
d) a combination of the above.
SGOT = serum glutamic oxaloacetic transaminase; AST = aspartate aminotransferase; SGPT = serum glutamate pyruvate transaminase; ALT = alanine aminotransferase
A normally sterile site is defined as blood, CSF, pleural fluid, peritoneal fluid, pericardial fluid, deep tissue specimen taken during surgery (e.g. muscle collected during debridement for necrotizing fasciitis), bone or joint fluid. This does not include middle ear or superficial wound aspirates.
Pneumonia with isolation of GAS from a sterile site, or from a bronchoalveolar lavage (BAL) when no other cause has been identified, should be regarded as aformofinvasivediseasefor thepurposesofpublic health management; however, as BAL does not provide a sterile site specimen, the latter would not meet the national case definition and would not be nationally notifiable.
5.2 Definitions for public health management
Tables 2 and 3 provide definitions of cases and close contacts.
|Sporadic case||AsinglecaseofinvasiveGAS diseaseoccurring in a community where there is no evidence of an epidemiologic link (by person, place or time) to another case.|
|Index case||The first case identified in an organization-or community-based outbreak. Identifying the index case in an outbreak is important for the characterization and matching of GAS isolate strains.|
|Subsequent||A case with onset of illness occurring within|
|case||21 days and caused by the same strain as another case (including sporadic or index cases) and with whom an epidemiologic link can be established. Most subsequent cases in the community will occur within 7 days of another case.|
|Severe case||Case of STSS, soft-tissue necrosis (including NF,myositisorgangrene),meningitis, GAS pneumonia, other life-threatening conditions or a confirmed case resulting in death.|
An epidemiologic link can be established when a person has one or both of the following in common with a confirmed case:
- contact with a common, specific individual (including confirmed or probable cases);
- presence in the same location (e.g. school, LTCF, child care centre) at or around the same time.
For public health management, cases that occur after the index case with whom an epidemiologic link can be established may have acquired the disease directly from the index case or from another common source.
- Household contacts of a case who have spent at least 4 hours/day on average in the previous 7 days or 20 hours/week with the case
- Non-household persons who share the same bed with the case or had sexual relations with the case
- Persons who have had direct mucous membrane contact with the oral or nasal secretions of a case (e.g. mouth-tomouth resuscitation, open mouth kissing) or unprotected direct contactwithanopenskinlesionofthe case
- Injection drug users who have shared needles with the case
- Selected LTCF contacts (see Section 6.3)
- Selected child care contacts (see Section 6.4)
- Selected hospital contacts (see Annex 3)
In order to be considered a close contact, there must have been exposure to the case during the period from 7 days prior to onset of symptoms in the case to 24 hours after the case's initiation of antimicrobial therapy. School classmates (kindergarten and older), work colleagues, as well as social or sports contacts of a case are not usually considered close contacts, unless they fit into one of the categories in Table 3.
An outbreak is defined as increased transmission of GAS causing invasive disease in a population. Outbreaks of invasive GAS disease do not occur in the community frequently and typically involve two cases (i.e. case-pairs) who have had close contact(17,22,23). Criteria defining the impetus for action for organization-based outbreaks or clusters are found in Table 4.
Table 4. Impetus for Action for Organization-based Outbreaks or Clusters
|Long-term care facility||An incidence rate of culture-confirmed invasive GAS infections of > 1 per 100 residents per month or at least two cases of culture-confirmed invasive GAS infection in 1 month in facilities with fewer than 200 residents or an incidence rate of suggested invasive or non-invasive GAS infections of > 4 per 100 residents per month.|
|Child care centre||One severe case of invasive GAS disease in a child attending a child care centre.|
|Hospital||One or more linked invasive or non-invasive GAS cases in either patients or staff occurring within 1 month of an invasive GAScase(seeAnnex3).|
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