Respiratory diphtheria was one of the most common causes of death among children 
in the pre-vaccine era. Since the introduction of diphtheria toxoid vaccine in 
1920s, and its widespread use by the late 1940s, diphtheria became increasingly 
rare in the United States. However, through the 1970s diphtheria remained 
endemic in some states, with reported incidence rates > 1.0 per million 
population in six states (Alaska, Arizona, Montana, New Mexico, South Dakota, 
and Washington). Starting in 1980, less than five cases have been reported each 
year in the United States. The majority of culture-confirmed cases have been 
associated with importation from other countries. Toxigenic Corynebacterium 
diphtheriae, the organism causing diphtheria, was thought to have become rare or 
even have disappeared from previously endemic areas such as South Dakota. 
However, during four months in 1996, 11 persons (one index case, six patients 
and four household contacts) in an American Indian community in South Dakota 
were found to be infected by C. diphtheriae; six of these isolates were 
toxigenic. The findings in this report indicate that despite 20 years without 
reported respiratory diphtheria cases, toxigenic C. diphtheriae is still present 
in South Dakota. The continuous circulation of toxigenic strains of C. 
diphtheriae emphasizes the need for health care providers throughout South 
Dakota to promote timely vaccination against diphtheria among persons of all 
ages and ethnic groups, to be aware of the clinical signs and symptoms of 
diphtheria so that cases can be promptly diagnosed and treated, and further 
public health measures can be taken to contain this serious disease.