Disease Risk – Diphtheria

 

Risk to a child from Diphtheria if not vaccinated until the age of 5

Diphtheria is an infectious disease caused by the bacterium Corynebacterium diphtheriae. It primarily affects the mucous membranes of the respiratory tract (respiratory diphtheria), although it may also affect the skin (cutaneous diphtheria) and lining tissues in the ear.  Prior to vaccination, diphtheria was endemic.  In historical times, classical naso-pharyngeal Diphtheria resulted in relatively high rates of mortality in young children although like most diseases morbidity and case fatality rates differed significantly between communities, likely reflecting differences in standards of living.[1]  The Diphtheria vaccine is toxoid-based and thus does not protect the individual from infection, but instead from the effects of the toxin produced by the bacteria.  Mass vaccination initiated in the 1940’s combined with improved living conditions has gradually resulted in only a handful of annual cases of diphtheria infection from North America.[2]  However, because vaccination does not confer immunity to the disease, the pathogen still exists and outbreaks can recur if living and health conditions decline sufficiently as witnessed in the former Russian republics in the 1990’s.

Case Fatality Rates: The case fatality rates largely vary depending on the age of the patient and the type of diphtheria infection.  Dixon observed that case fatality rates have remained relatively constant over time but that local variations between locations could be quite drastic[1].  The CDC lists case fatality rates of up to 20% in persons younger than 5 and older than 40.  Using data from the recent outbreaks in Russia, the highest case fatality rate was 13% for unvaccinated children < 18 years while the rate for fully vaccinated children was 0.5%.[3]  This analysis will use a rate of 13%.

Rates of Long Term Sequelae or Injury: Although there are several complications that can occur from Diphtheria infection, there is little documentation regarding long term sequelae.  This analysis will use a long term sequelae rate of 0.

Incremental Risk in Highly Vaccinated Population (if a child does not vaccinate by age 5): In the past five years there has not been a single reported case of diphtheria within the United States[1].  Diphtheria is no longer circulating within the United States and so the risk posed to an individual child electing not to receive the diphtheria vaccine is zero provided that herd immunity, adequately clean water supply and basic sanitation are maintained.

Incremental Risk in Population with Low Rates of Vaccination (if a child does not vaccinate by age 5): The most recent outbreak of Diphtheria in modern times occurred in the former Russian republics during the 1990s.  In populations with low rates of vaccination, diphtheria outbreaks occur in waves so this analysis uses the incidence rates over the peak 5 years ending in 1996.[4]  The 5 year incidence rates per 100,000 population used are:  1.93, 6.55, 16.04, 16.98 and 6.81 (ending in 1996).  The cumulative risk of death over the 5 years is calculated to be 6 per 100,000 or 1 in 15,925.

References:

[1] Dixon, JMS.  Diphtheria in North America.  J Hyg. Camb (1984), 93, 419-432

[2] Centers for Disease Control and Prevention: Epidemiology and Prevention of Vaccine-Preventable Disease. Atkinson W, Wolfe S, Hamborsky J, McIntyre L. eds. 11th edition. Washington D.C.: Public Health Foundation, 2009.

[3]  Vitek CR, Brisgalov SP, Bragina VY, Zhilyakov AM, Bisgard KM, Brennan M, Kravtsova ON, Lushniak BD, Lyerla R, Markina SS, Strebel PM.  Epidemiology of epidemic diphtheria in three regions, Russia, 1994-1996.  Eur J Epidemiol. 1999 Jan;15(1):75-83.

[4]  Vitek CR, Wharton M.  Diphtheria in the former Soviet Union: reemergence of a pandemic disease.  Emerg Infect Dis. 1998 Oct-Dec;4(4):539-50.