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Diphtheria (Corynebacterium diphtheriae)
2019 Case Definition

NOTE: A surveillance case definition is a set of uniform criteria used to define a disease for public health surveillance. Surveillance case definitions enable public health officials to classify and count cases consistently across reporting jurisdictions. Surveillance case definitions are not intended to be used by healthcare providers for making a clinical diagnosis or determining how to meet an individual patient’s health needs.

CSTE Position Statement(s)

  • 18-ID-03

Background

Diphtheria is caused by toxin-producing Corynebacterium diphtheriae (C. diphtheriae). This disease primarily manifests as respiratory infections that may result in death, but it may also present as mild infections in non-respiratory sites, such as the skin. While respiratory diphtheria is now extremely rare, non-respiratory infections caused by toxin-producing bacteria have recently been detected. Non-respiratory disease caused by toxin-producing C. diphtheriae may act as a source of transmission and can lead to new respiratory and non-respiratory diphtheria disease; both respiratory and non-respiratory disease caused by toxin-producing bacteria require public health follow-up. This diphtheria surveillance case definition better reflects the epidemiology of diphtheria in the U.S, in order to focus efforts on identifying disease caused by toxin-producing bacteria and appropriately guide public health interventions.

Clinical Criteria

  • Upper respiratory tract illness with an adherent membrane of the nose, pharynx, tonsils, or larynx OR
  • Infection of a non-respiratory anatomical site (e.g., skin, wound, conjunctiva, ear, genital mucosa)

Laboratory Criteria for Diagnosis

Confirmatory laboratory evidence:

  • Isolation of C. diphtheriae from any site AND
  • Confirmation of toxin-production by Elek test or by another validated test capable of confirming toxin-production

Supportive laboratory evidence:

  • Histopathologic diagnosis

Epidemiologic Linkage

Epidemiologic linkage requires direct contact with a laboratory-confirmed case of diphtheria.

Criteria to Distinguish a New Case from an Existing Case

Individuals without evidence of clinical criteria as described by the diphtheria surveillance case definition but for whom toxin-producing Corynebacterium diphtheriae is confirmed via laboratory testing (isolation and toxigenicity testing by modified Elek test or other validated test capable of confirming toxin-production) should not be classified as cases. These individuals are considered carriers of the bacteria and are not reportable.

Case Classification

Suspected

  • In the absence of a more likely diagnosis, an upper respiratory tract illness with each of the following:
    • an adherent membrane of the nose, pharynx, tonsils, or larynx AND
    • absence of laboratory confirmation AND
    • lack of epidemiologic linkage to a laboratory-confirmed case of diphtheria.
    OR
  • Histopathologic diagnosis

Confirmed

  • An upper respiratory tract illness with an adherent membrane of the nose, pharynx, tonsils, or larynx and any of the following:
    • isolation of toxin-producing Corynebacterium diphtheriae from the nose or throat OR
    • epidemiologic linkage to a laboratory-confirmed case of diphtheria.
    OR
  • An infection at a non-respiratory anatomical site (e.g., skin, wound, conjunctiva, ear, genital mucosa) with
    • isolation of toxin-producing C. diphtheriae from that site

Case Classification Comments

  • Cases of laboratory-confirmed, non-toxin-producing C. diphtheriae (respiratory or non-respiratory) should not be reported by state or local health departments to CDC as diphtheria cases.
  • Negative laboratory results may be sufficient to rule-out a diagnosis of diphtheria; however, clinicians should carefully consider all lab results in the context of the patient's vaccination status, antimicrobial treatment, and other risk factors.
  • PCR (polymerase chain reaction) and MALDI-TOF (matrix assisted laser desorption/ionization-time of flight mass spectrometry) diagnostics for C. diphtheriae, when used alone, do not confirm toxin production. These tests, when used, should always be combined with a test that confirms toxin production, such as the Elek test.




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