Diphtheria Facts (cont.)

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What causes diphtheria?

The cause of diphtheria is bacterial species termed Corynebacterium diphtheriae, a gram-positive bacillus that usually produces exotoxins. There are three main strains of C. diphtheriae: gravis, intermedius, and mitis. The strain termed intermedius is most often associated with exotoxin production although all three strains are capable of producing exotoxin. The organisms easily invade the tissue lining the throat, and during that invasion, they produce exotoxins that destroy the tissue and lead to the development of a pseudomembrane. The exotoxin production is dependent upon a viral genome that is present within the bacteria. This viral genome is copied when the bacteria multiplies; if the viral genome is lost, diphtheria exotoxin is not produced. Non-toxin-producing strains and other Corynebacterium species such as C. ulcerans can still cause infection, but infection is less severe and sometimes remains only in the skin (cutaneous infection).

What are risk factors for diphtheria?

Because human carriers or symptomatic individuals are the main reservoir for infection, situations such as overcrowding (dormitories, institutional housing, poor living conditions), incomplete immunization, and people who are immunodepressed are at higher risk for getting diphtheria. Diphtheria is transmitted by inhalation of airborne droplets or by direct contact with infected patients by mucous secretions or skin ulcerations. Some people may carry the bacteria in their respiratory tracts (termed carriers) but do not exhibit disease. However, such individuals can still transmit the organisms to uninfected individuals.

How do physicians diagnose diphtheria?

Preliminary diagnosis of diphtheria is usually made from the patient's history and physical exam and the presence of a pseudomembrane formation in the throat. Confirmation is based on isolation of the organism from swab specimens taken from the throat or from skin lesions. However, because diphtheria can be lethal, the CDC recommends immediate treatment if diphtheria suspected; do not wait for laboratory confirmation.

Medically Reviewed by a Doctor on 12/8/2014

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