Diphtheria is an acute toxic infection caused by Corynebacterium diphtheriae, an aerobic, non-encapsulated, gram positive bacillus. C.diphtheriae is an exclusive inhabitant of human mucous membranes and skin. It spreads primarily by airborne respiratory droplets, direct contact with respiratory secretions or exudates from infected skin lesions. Diphtheria is endemic in developing countries of Africa, Asia and South America. Incidence peaks during autumn and winter and majority of cases occur in unimmunized children below 15 years of age.

Diphtheria occurs by entry of C.diphtheriae into the nose or mouth and after a 2-4 day incubation period, toxins are secreted which leads to toxin mediated tissue necrosis. This coupled with local inflammatory response produces patchy exudates which later forms fibrinous exudates and a tough adherent membrane. Respiratory embarrassment may follow extension of disease into larynx or tracheobronchial tree.

Toxin is distributed via blood stream & lymphatics throughout the body. Any organ or tissue can be damaged as a result of diphtheria toxin, but lesions of the heart, nervous system and kidneys are particularly prominent. Clinical manifestations appear after a latent period ranging from 10-14 days for myocarditis and from 3 to 7 weeks for nervous system manifestations such as peripheral neuritis. Antitoxin can neutralize circulating toxin or toxin that is absorbed to cells but is ineffective once cell penetration has occurred. Thus early treatment is essential to limiting tissue damage.

The signs and symptoms of diphtheria will depend upon the site of infection, the immunization status of the host and whether or not toxin has been distributed to the systemic circulation.

In tonsillar and pharyngeal diphtheria, sore throat is a universal early symptom. Underlying soft tissue edema and enlarged lymph nodes may cause a bull-neck appearance.

Complications remain the greatest cause of morbidity and mortality following infection with diphtheria. Complications secondary to the elaborated diphtheria toxin are the most common. Myocarditis most commonly occurs in the second week of the disease but can appear as early as the first or as late as the sixth week of illness. Tachycardia, muffled first heart sound, murmurs and arrhythmias such as atrioventricular dissociation are indicative of myocardial involvement. Although some cases may result in cardiac failure, the majority of myocardial complications are temporary. Neurologic complications appear after a variable latent period, are predominantly bilateral are motor rather than sensory and usually resolve completely. Paralysis of the soft palate is common and generally appears in the 3rd week. Ocular paralysis usually occurs in the 5th week of illness. Paralysis of diaphragm, peripheral neuropathy are known complications. Gastritis hepatitis, nephritis and hemolytic uremic syndrome have been reported as complications of diphtheria.

Diagnosis of diphtheria should be made on basis of clinical findings, because any delay in therapy may pose a serious risk to patient. Examination of direct smear and isolation of organism from culture are important. The laboratory should be notified about the possibility of diphtheria so that appropriate culture media are inoculated.

Specific antitoxin is the main stay of therapy and should be administered as early as possible by intravenous route and in a dosage sufficient to neutralize the free toxin. Equine diphtheria anti toxin is available and administered as a single empirical dose of 20,000 – 1,20,000 U based on degree of toxicity, site and size of membrane and duration of illness.

Antibiotics such as erythromycin (40-50 mg/kg/d) or penicillin G (1,00,000 – 1,50,000U/kg/d) for 14 days are indicated to halt toxin production, treat localized infection and prevent transmission of organisms to contacts. Bed rest is essential usually for 2 weeks or more until the risk of symptomatic cardiac damage has passed. Serial electrocardiograms should be obtained 2 or 3 times each week for 4-6 weeks to detect myocarditis as early as possible. The patient with myocarditis may be digitalized if CCF develops. However, digitalization for arrhythmias due to diphtheria may be contraindicated. In severe disease, prednisolone, 1 to 1.5 mg/kg/day for 2 weeks has been shown to lessen the incidence of myocarditis. The quality of voice and gag reflex should be checked regularly for assessment of progression of the disease. At least half of the patients who recover from diphtheria will not develop adequate immunity. Therefore, immunization is indicated after the recovery of the patient. Recovery from myocarditis and neuritis is often slow but complete.

Primary prevention in form of active immunization as DPT vaccine at 2,4,6 months of age and booster dose at 15-18 months and again between 4-6 years of age is recommended. All household contacts and those who have had intimate respiratory or habitual physical contact with a patient are closely monitored for illness through the 7-day incubation period. Cultures of the nose, throat and any cutaneous lesions are performed. Antibiotic prophylaxis is given, regardless of immunization status using erythromycin (40-50 mg/kg/day) for 7-days or a single injection of benzathine penicillin.