1. Definition and agent factors
2. Epidemiological determinants: agent, reservoir, source, transmission, incubation, communicability, host and environmental factors
3. Clinical features, complications and diagnosis
4. Prevention: immunization schedule, vaccine efficacy and contraindications
5. Surveillance, notification, outbreak investigation and control
6. Case management, isolation, contact management and chemoprophylaxis

1. Definition and agent factors
2. Epidemiological determinants: agent, reservoir, source, transmission, incubation, communicability, host and environmental factors
3. Clinical features, complications and diagnosis
4. Prevention: immunization schedule, vaccine efficacy and contraindications
5. Surveillance, notification, outbreak investigation and control
6. Case management, isolation, contact management and chemoprophylaxis

1. Epidemiological determinants of diphtheria
2. Diphtheria immunization schedule
3. Case, contact and outbreak-control measures
4. Complete diphtheria topic, given section by section

Epidemiological determinants of diphtheria

1. Agent factors

2. Reservoir and source of infection

1. Clinical cases
   • May range from subclinical/mild illness to obvious clinical diphtheria.
   • Mild or silent cases, presenting only with running nose or sore throat, may be epidemiologically important because they can spread infection unnoticed.
2. Carriers
   • Carriers are a common source of infection.
   • They may be:
     • Temporary or chronic
     • Nasal or throat carriers
   • Nasal carriers are more dangerous than throat carriers because they shed bacilli more frequently into the environment.
   • Temporary carriage may last about 1 month.
   • Chronic carriage may continue for a year or longer if untreated.
   • Immunization protects against toxin-mediated disease but does not necessarily prevent the carrier state.

3. Infective material

• Nasopharyngeal secretions
• Discharge from skin lesions
• Contaminated fomites
• Possibly infected dust

4. Period of infectivity / communicability

• In untreated cases, infectivity may persist for 14 to 28 days from onset.
• Carriers may remain infective for much longer.
• A case or carrier is considered non-communicable after two negative cultures from properly collected nose and throat swabs, taken 24 hours apart.
• Current CDC guidance similarly states that communicability continues while virulent bacilli are present in discharges or lesions, and effective antibiotics rapidly stop shedding. CDC epidemiology section

5. Host factors

A. Age

• Traditionally, diphtheria mainly affects children aged 1-5 years.
• With widespread childhood vaccination, the age distribution shifts from preschool children to school-age children, adolescents and adults, owing to waning immunity and inadequate booster doses.

B. Sex

• Both sexes are equally affected.

C. Immunity

• Infants born to immune mothers have relative protection during the first few weeks or months of life due to maternal antibodies.
• Before widespread immunization, inapparent infection, including cutaneous infection, produced natural immunity in many people.
• Clinical diphtheria usually occurs in persons with absent or inadequate circulating antitoxin, conventionally stated in Park as less than 0.01 Lf unit/mL.
• Protection depends primarily on adequate neutralizing antitoxin from documented primary vaccination and booster doses.

D. Susceptibility

• Unimmunized persons
• Partially immunized persons
• Persons who missed booster doses
• People living in overcrowded settings
• Displaced populations, migrants and communities with disrupted vaccine supply or health services

6. Environmental factors

• Diphtheria occurs in all seasons, but winter months favor spread.
• In temperate countries, winter and spring predominance is often reported.
• Factors promoting transmission and outbreaks include:
  • Overcrowding
  • Poor hygiene
  • Low routine immunization coverage
  • Failure to give booster doses
  • Population displacement or migration
  • Irregular vaccine availability
  • Weak surveillance and delayed case detection

7. Mode of transmission

1. Droplet infection
   • Main mode of spread.
   • Infection spreads by respiratory droplets from coughing, sneezing or close contact with an infected person/carrier.
2. Direct contact
   • Direct transfer from infected cutaneous lesions to a susceptible person.
3. Indirect transmission
   • Through articles contaminated by nasopharyngeal secretion, such as:
     • Cups
     • Toys
     • Thermometers
     • Pencils
   • Fomite transmission is possible but usually for short periods only.

8. Portal of entry

9. Incubation period

• 2-6 days, occasionally longer according to Park.
• Contemporary sources commonly cite 2-5 days, range 1-10 days. CDC clinical epidemiology

10. Occurrence and epidemiological pattern

Globally

• Diphtheria is now rare in high-income countries due to successful routine immunization.
• It remains endemic or can re-emerge in settings with poor vaccination coverage.
• Outbreaks occur when routine immunization declines, immunity wanes in older age groups, vaccine supply is interrupted, or populations are displaced.
• Recent outbreaks have demonstrated an age shift toward older children and adults.

India

• Park describes diphtheria as endemic in India, with a declining trend associated with improved childhood immunization coverage.
• However, case numbers and geographic distribution change over time, so current national surveillance data should be used for contemporary figures rather than older textbook statistics.

Short exam answer: determinants in one list