Chapter 131. Diphtheria and Other Infections Caused by Corynebacteria and Related Species (Part 4)

DiagnosisThe diagnosis of diphtheria is based on clinical signs and symptoms plus laboratory confirmation. Respiratory diphtheria should be considered in patients with sore throat, pharyngeal exudates, and fever. Other symptoms may include hoarseness, stridor, or palatal paralysis. The presence of a pseudomembrane should prompt consideration of diphtheria. Once a clinical diagnosis of diphtheria is made, diphtheria antitoxin should be administered as soon as possible.Laboratory diagnosis is based either on cultivation of C. diphtheriae or toxigenic C. ulcerans from the site of infection or on the demonstration of local lesions with characteristic histopathology. ...
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Chapter 131. Diphtheria and Other Infections Caused by Corynebacteria and Related Species (Part 4) Chapter 131. Diphtheria and Other Infections Caused by Corynebacteria and Related Species (Part 4) Diagnosis The diagnosis of diphtheria is based on clinical signs and symptoms pluslaboratory confirmation. Respiratory diphtheria should be considered in patientswith sore throat, pharyngeal exudates, and fever. Other symptoms may includehoarseness, stridor, or palatal paralysis. The presence of a pseudomembraneshould prompt consideration of diphtheria. Once a clinical diagnosis of diphtheriais made, diphtheria antitoxin should be administered as soon as possible. Laboratory diagnosis is based either on cultivation of C. diphtheriae ortoxigenic C. ulcerans from the site of infection or on the demonstration of locallesions with characteristic histopathology. C. pseudodiphtheriticum, anontoxigenic organism, is a common component of the normal throat flora anddoes not pose a significant risk. Throat samples should be submitted to thelaboratory for culture with the notation that diphtheria is being considered. Thisinformation should prompt cultivation on special selective medium andsubsequent biochemical testing to differentiate C. diphtheriae from othernasopharyngeal commensal corynebacteria. All laboratory isolates of C.diphtheriae, including nontoxigenic strains, should be submitted to the CDC. A diagnosis of cutaneous diphtheria requires laboratory confirmation sincethe lesions are not characteristic and are clinically indistinguishable from otherdermatoses. Diphtheritic ulcers occasionally—but not consistently—have apunched-out appearance (Fig. 131-2). Patients in whom cutaneous diphtheria isidentified should have the nasopharynx cultured for C. diphtheriae. The laboratorymedia for cutaneous diphtheria are the same as those used for respiratorydiphtheria: Löfflers or Tinsdales selective medium in addition to nonselectivemedium such as blood agar. As has been mentioned, respiratory diphtheriaremains a notifiable disease in the United States, whereas cutaneous diphtheria isnot. Diphtheria: Treatment Diphtheria Antitoxin Prompt administration of diphtheria antitoxin is critical in the managementof respiratory diphtheria. The antitoxin—a horse antiserum—is effective inreducing the extent of local disease as well as the risk of complications ofmyocarditis and neuropathy. Rapid institution of antitoxin therapy is alsoassociated with a significant reduction in mortality risk. Because diphtheriaantitoxin cannot neutralize cell-bound toxin, prompt initiation is important. Thisproduct, which is no longer made commercially in the United States, is availablefrom the CDC under an investigational new drug protocol and may be obtained bycalling the Bacterial Vaccine Preventable Disease Branch of the NationalImmunization Program at 404-639-8257 between 8:00 A.M. and 4:30 P.M. U.S.Eastern time or at 770-488-7100 at other hours; the relevant website ishttp://www.cdc.gov/nip/vaccine/dat/default.htm. The current protocol for the useof antitoxin includes a test dose to rule out immediate-type hypersensitivity.Patients who exhibit hypersensitivity require desensitization before a fulltherapeutic dose of antitoxin is administered. Antimicrobial Therapy Antibiotics are used in the management of diphtheria primarily to preventtransmission to other susceptible contacts. Recommended options for the treatmentof patients with respiratory diphtheria are as follows: (1) procaine penicillin G at adosage of 600,000 units (for children, 12,500–25,000 U/kg) IM every 12 h untilthe patient can swallow comfortably, after which oral penicillin V is given at 125–250 mg four times daily to complete a 14-day course; or (2) erythromycin at adosage of 500 mg IV every 6 h (for children, 40–50 mg/kg per day IV in two orfour divided doses) until the patient can swallow comfortably, after which 500 mgis given PO four times daily to complete a 14-day course. A clinical study in Vietnam found that penicillin was associated with amore rapid resolution of fever and a lower rate of bacterial resistance thanerythromycin; however, relapses were more common with penicillin.Erythromycin therapy targets protein synthesis and thus offers the presumedbenefit of stopping toxin synthesis more quickly than a cell wall–active β-lactamagent. Alternative agents for patients who are allergic to penicillin or cannot takeerythromycin include rifampin and clindamycin. Eradication of C. diphtheriaeshould be documented at least 1 day after antimicrobial therapy is complete. Arepeat throat culture 2 weeks later is recommended. For patie ...