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Shigellosis (Shigella spp.)
2017 Case Definition

Clinical Criteria

An illness of variable severity commonly manifested by diarrhea, fever, nausea, cramps, and tenesmus. Asymptomatic infections may occur.

Laboratory Criteria for Diagnosis

Supportive laboratory evidence: Detection of Shigella spp. or Shigella/ enteroinvasive E. coli (EIEC) in a clinical specimen using a culture-independent diagnostic testing (CIDT).

Confirmatory laboratory evidence: Isolation of Shigella spp. from a clinical specimen.

Epidemiologic Linkage

A clinically compatible case that is epidemiologically linked to a case that meets the supportive or confirmatory laboratory criteria for diagnosis.

Criteria to Distinguish a New Case from an Existing Case

A case should not be counted as a new case if laboratory results were reported within 90 days of a previously reported infection in the same individual.

When two or more different serotypes are identified in one or more specimens from the same individual, each should be reported as a separate case.

Case Classification

Probable

  • A case that meets the supportive laboratory criteria for diagnosis; OR
  • A clinically compatible case that is epidemiologically linked to a case that meets the supportive or confirmatory laboratory criteria for diagnosis.

Confirmed

A case that meets the confirmed laboratory criteria for diagnosis.

Comments

The use of CIDTs as stand-alone tests for the direct detection of Shigella/EIEC in stool is increasing. EIEC is genetically very similar to Shigella and will be detected in CIDTs that detect Shigella. Specific performance characteristics such as sensitivity, specificity, and positive predictive value of these assays likely depend on the manufacturer and are currently unknown. It is therefore useful to collect information on the type(s) of testing performed for reported shigellosis cases. When a specimen is positive using a CIDT, it is also helpful to collect information on all culture results for the specimen, even if those results are negative.

Culture confirmation of CIDT-positive specimens is ideal, although it might not be practical in all instances. State and local public health agencies should make efforts to encourage reflexive culturing by clinical laboratories that adopt culture-independent methods, should facilitate submission of isolates/clinical material to state public health laboratories, and should be prepared to perform reflexive culture when not performed at the clinical laboratory. Isolates are currently necessary for molecular typing (PFGE and whole genome sequencing) that are essential for outbreak detection and for antimicrobial susceptibility testing, which is increasingly important because of substantial multidrug resistance among Shigella.



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