Health Hygiene & Sanitation

Lesson 37 : Prevention Of Respiratory Infections


Diphtheria is an acute infectious disease caused by toxigenic strains of Corynebacterium diphtheriae. Three major types of diphtheria have been reported- anterior nasal, faucial and laryngeal: however, the skin, conjunctiva, vulva and other parts of the body may be affected. The bacilli multiply in the throat and elaborate a powerful exotoxin. The toxin is responsible for:

  • Formation of a greyish or yellowish membrane ("false membrane") over the tonsils, pharynx or larynx (or at the site of implantation);
  • Marked congestion, oedema or local tissue, destruction;
  • Enlargement of the regional lymph nodes; and
  • Signs and symptoms of toxemia.

Fatality rate on the average is about 5 and 10 per cent in treated and untreated cases respectively.

Agent Factors:

  • Agent: the causative agent of diphtheria is Corynebacterium diphtheria produces a powerful exotoxin. Three types are pathogenic to man-gravis, mitis and intermedius.

  • Reservoir of Infection: Nasopharyngeal secretions, discharges from skin lesions, contaminated fomites, and infected dust.

  • Source of Infection: Usually a case or carrier.

  • Period of Infectivity: Unless treated it varies from14 to 28 days.

Host Factors:

  • Age and Sex: Diphtheria affects children aged 1 to 5 and both sexes. In case of prompt immunization a shift in the age of occurrence has been observed from preschool age to school age.

  • Immunity: Immunity to diphtheria is seen among children born to immune mothers. About 70 and 99 per cent of the children above the age of 3 and 5 years respectively are immune to diphtheria.

Environmental Factors:

All seasons witness diphtheria, however, winter is more ideal for its spread.

Mode of Transmission:

The disease is spread mainly by droplet infection. It can also be transmitted directly to susceptible persons from infected skin lesions.

Portal of Entry:

Respiratory tract is the common portal of entry. Sometimes it can be skin, umbilicus of the new born. Occasionally it can be eye, middle ear or genitalia

Incubation Period: 2 to 6 days

Clinical Features: sore throat, difficulty in swallowing low grade fever, hoarseness, croupy cough.


  • Cases and Carriers: early detection, isolation, treatment help in control of the disease.

  • Contacts: person in contact with the patient should be determined for immunity status and treated accordingly.

  • Community: active immunization of infants as early in life as possible is the only means of control of diphtheria. DPT is the vaccine of choice to protect infants from three deadly diseases-diphtheria, pertussis and tetanus.
Last modified: Friday, 27 April 2012, 5:53 AM