infectious diseases
Diphtheria
Diagnosis of Diphtheria
Gram stain and culture Pharyngeal diphtheria needs to be considered in patients with nonspecific findings of pharyngitis, cervical adenopathy, and low-grade fever if they also have systemic toxicity plus hoarseness, palatal paralysis, or stridor. The appearance of the characteristic membrane suggests the diagnosis. Gram stain of a specimen from the membrane may reveal gram-positive bacilli with metachromatic (beaded) staining in typical Chinese-character configuration, with club-shaped swelling at one or both ends. Material for culture should be obtained from below the membrane, or a portion of the membrane itself should be submitted. The laboratory should be notified thatC. diphtheriaeis suspected, so that special culture media (Loeffler or Tindale) can be used. In vitro testing for toxin production (modified Elek test) is done to differentiate toxigenic from nontoxigenic strains. Polymerase chain reaction testing for the diphtheria toxin gene can be done. Cutaneous diphtheria should be considered when a patient develops skin lesions during an outbreak of respiratory diphtheria. Swab or biopsy specimens should be cultured. Cutaneous diphtheria lesions may be coinfected with group A streptococci orStaphylococcus aureus. ECG should be done to look for ST-T wave changes, QTc prolongation, and/or 1st-degree heart block related to myocarditis, which often becomes evident as the respiratory symptoms resolve. 