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-producingCorynebacterium 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-producingCorynebacterium 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-producingC.diphtheriae from that site
Case Classification Comments
Cases of laboratory-confirmed,non-toxin-producingC.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.