Diphtheria

Diphtheria is a serious infectious disease caused by strains of the bacterium Corynebacterium diphtheriae that produce a diphtheria toxin. The toxin damages tissues, most commonly attaching to the respiratory system where it kills healthy tissue and forms a characteristic pseudomembrane. The disease is classified under ICD-10 code A36 and ICD-11 code 1C15, and is included in the bacterial disease category.

The incubation period typically ranges from 2 to 5 days after exposure. Initial symptoms include sore throat, fever, swollen neck glands, and weakness, which may progress gradually. Within 2 to 3 days, dead respiratory tissue forms a thick grey or white pseudomembrane that can cover the nose, tonsils, and throat, obstructing breathing and swallowing. The toxin may enter the bloodstream and cause systemic complications including myocarditis, nerve inflammation, kidney problems, and bleeding disorders. While most infections are asymptomatic or mild, severe disease can be fatal in approximately 30% of unvaccinated individuals without adequate treatment, with mortality approaching 10% in some outbreak settings.

Diphtheria was historically common worldwide before widespread vaccination in the 1930s. The disease can affect anyone but historically predominated in unvaccinated children. No WHO region is currently free from diphtheria, and outbreaks have occurred with increasing frequency in areas with low immunization coverage. The COVID-19 pandemic disrupted routine immunization services and surveillance activities, leaving many children susceptible to vaccine-preventable diseases. Areas with inadequate diphtheria toxoid-containing vaccine coverage allow the bacteria to circulate, increasing outbreak likelihood and placing unvaccinated and under-vaccinated individuals at risk.

Diphtheria spreads primarily through respiratory droplets when infected individuals cough or sneeze. Some infected persons may be asymptomatic carriers yet still transmit the bacteria to others. Transmission can also occur through direct contact with infected open sores or ulcers, and indirectly via contaminated surfaces or objects where bacteria remain viable. Household contacts and those with frequent close contact with infected individuals face elevated exposure risk.

Any non-immune person who is unvaccinated or under-vaccinated remains susceptible to infection. Populations at elevated risk include household contacts of confirmed cases, individuals with frequent close contact with infected persons, and those in settings with compromised health infrastructure. Overcrowded conditions in residential or displacement camps increase transmission risk. Children under 5 years of age face greater risk of severe outcomes and death. Immunization coverage gaps in any community create conditions for resurgence, particularly in areas affected by conflict, natural disasters, or health system disruptions.

Diphtheria is preventable through vaccination with diphtheria toxoid-containing vaccines, which are safe, effective, and typically administered in combination with tetanus, pertussis, and other antigens. WHO recommends a 3-dose primary vaccination series beginning at 6 weeks of age, followed by 3 booster doses through adolescence, totaling 6 doses for long-term protection. Community-wide vaccination with high coverage embedded in routine primary healthcare services represents the most effective prevention strategy. All children should receive the complete primary series and booster doses to maintain population immunity.

Surveillance for diphtheria requires clinical recognition of the characteristic pseudomembrane and respiratory symptoms combined with laboratory confirmation. The disease serves as an indicator of immunization program performance; increases in case numbers typically signal gaps in vaccination coverage or disruptions to routine immunization services. Enhanced surveillance is particularly important in post-conflict settings, disaster-affected areas, and during or after public health emergencies that have impacted routine health services. Asymptomatic carriers complicate detection, making contact tracing and outbreak investigation essential components of surveillance response.

1. 1 WHO Health Topics. Diphtheria.
2. 2 WHO Fact Sheet. Diphtheria.
3. 3 WHO Q&A. Diphtheria.
4. 4 Wikidata. diphtheria.
5. 5 Wikipedia. Diphtheria - Wikipedia.

ICD-10

A36

ICD-11

1C15

Total cases

339

Total deaths

9

Peak month

2026-04

Coverage

3 reporting countries · 2000-01-01 → 2026-05-02