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[Gr. diphthera, hide, membrane + -ia]
A rare, contagious, toxin-mediated bacterial disease marked by the formation of a patchy grayish-green membrane over the tonsils, uvula, soft palate, and posterior pharynx. Occasionally the skin, conjunctiva, ears, GI and urinary tracts are involved. In cutaneous diphtheria, impetiginous lesions occur. The membrane is created by a thick, inflammatory exudate.
SEE: antitoxin; SEE: exotoxin; SEE: sepsis; SEE: diphtheria toxoid
diphtherial (dif-thēr′ē-ăl)
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, adj.

An effective vaccination program has made the incidence of the disease rare in the U.S., except among those groups of people who do not receive immunizations. The lack of virulent strains to reinforce immunity, however, has resulted in loss of immunity in some older adults. In the 1920s, before vaccination, about 200,000 cases of diphtheria were reported annually. The current incidence is about 1 case per year.

The causative organism is Corynebacterium diphtheriae. Airborne droplets transmit the organism from person to person (usually from asymptomatic carriers or convalescent patients). More people carry the disease than actually contract an active infection. The incubation period is 2 to 5 days and occasionally longer.

Immunization is by administration of three doses at least 4 weeks apart, beginning at 2 months of age. Diphtheria toxoid (inactivated exotoxin capable of stimulating antibody production) is given in combination with pertussis vaccine (usually acellular pertussis) and tetanus toxoid; a fourth dose is given 1 year later. Booster doses are administered if a child under 6 years old or other close family member is exposed to diphtheria. Because effective immunity does not last longer than 10 years after the last vaccination, people should receive a booster of diphtheria toxoid every 10 years. Immunity to diphtheria is assessed by measuring antibody levels in the blood.

Patients present with fever, malaise, cervical lymphadenopathy, sore throat, raspy cough, hoarseness, and other croup-like symptoms. A tough yellow-white or gray-green pseudomembrane forms in the throat. It contains cellular debris and fibrin and, unlike the exudate caused by streptococci, is difficult to remove and can obstruct air flow. If not treated it may result in stridor, suprasternal retractions, tachypnea, cyanosis, and death by suffocation. As the bacteria multiply, they produce a potent exotoxin that prevents protein synthesis in cells. Once the exotoxin has spread to the bloodstream, signs of sepsis develop. The toxin can cause peripheral nerve paralysis, thrombocytopenia, renal and pulmonary involvement, and myocarditis, with ventricular fibrillation resulting in death.

Similar symptoms may be due to tonsillitis, scarlet fever, acute pharyngitis, streptococcal sore throat, peritonsillar abscess, infectious mononucleosis, necrotizing ulcerative gingivitis, acute moniliasis, primary HIV retroviral syndrome, and staphylococcal infections in the respiratory tract after chemotherapy. Examination of a smear from the infected area is advisable; cultures should be obtained in every instance to confirm the diagnosis. In the laryngeal type of diphtheria, edema of the glottis, foreign bodies, and retropharyngeal abscess must be considered.

If an adult or unimmunized child shows signs of infection, then diphtheria antitoxin, containing preformed antibodies, is administered immediately without waiting for laboratory confirmation. Because the antitoxin is made from animal serum, hypersensitivity must first be assessed with an intradermal injection of 1:10 dilute antitoxin. If testing is positive, desensitization should be attempted even though it is time-consuming and carries some risk. When antitoxin is administered, epinephrine 1:1000 and resuscitation equipment should be on standby, and the patient should be closely observed for anaphylaxis. Intravenous erythromycin administered for 7 to 14 days may decrease exotoxin production by C. diphtheriae and limit spread of the disease although it may sometimes cause thrombophlebitis.

The patient is monitored for respiratory distress, sepsis, and myocardial or neural involvement. Humidified oxygen is administered to maintain saturated hemoglobin (SaO2) above 92%, and the patient is assessed for increased ventilatory effort, use of accessory muscles, nasal flaring, stridor, cyanosis, and agitation or decreased level of consciousness. If airway obstruction occurs, intubation, tracheostomy, mechanical ventilation, or other life-support measures may be required. Hypotension, tachycardia, and crackles on auscultation may indicate heart failure. Sepsis may produce fever, tachycardia, and hypotension. Neuromuscular involvement is assessed through weakness, paralysis, or sensory changes. All data are clearly documented. Patients who receive antitoxin are closely observed for local or systemic anaphylaxis.

Strict isolation is maintained until two consecutive negative nasopharyngeal cultures have been obtained at least 1 week after drug therapy ceases. Unimmunized members of the patient's household are advised to receive diphtheria toxoid appropriate for age and to complete the proper series of immunizations. Even if previously immunized, a person should receive a booster immunization if more than 10 years have passed since the last vaccination. All cases of diphtheria must be reported to local public health authorities. Families must be prepared for a prolonged convalescence esp. if the patient has neuromuscular involvement.

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