OBJECTIVES: Clinical diphtheria is on the increase worldwide, mainly affecting 
developing countries. We sought to understand its presentation among patients at 
Sir Ronald Ross Institute of Tropical and Communicable Diseases in Hyderabad, 
Andhra Pradesh, India.
METHODS: Diphtheria patients presented with fever, pharyngitis, and a patch in 
the throat. Data collected for each patient included age, clinical presentation, 
morbidity, mortality, bacteria isolated from culture, and immunization status.
RESULTS: Of 61 950 admissions from January 2008 to December 2012, 2925 (4.7%) 
had clinical diphtheria; 1194 had been immunized and 1731 were non-immunized. 
Immunized patients had a milder disease. Culture-positive immunized patients 
were positive for Corynebacterium other than diphtheriae (COD; n=104) or 
Corynebacterium diphtheriae (CD; n=23); these patients suffered mild disease and 
recovered completely. In contrast, culture-positive non-immunized patients were 
positive for COD (n=11) or CD (n=412). Eighty-one patients (3%) died, 77 of whom 
were non-immunized; death was usually as a result of myocarditis. Seventy-three 
percent of deaths were in patients aged <5 years.
CONCLUSIONS: The clinical presentation of diphtheria and its severity and 
morbidity differ considerably in immunized and non-immunized patients. Disease 
caused by CD can be deadly, while disease due to COD is mild and responds to 
treatment.