Observations on the Bacteriology of an Epidemic of Diphtheria in a School, with Special Reference to the Virulence of the Organisms which were Isolated from the Cases

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Abstract
(1) A localised epidemic of diphtheria of a clinically mild type (both as regards local and general symptoms) was associated with the prevalence in the fauces of patients and contacts of strains of B. diphtheriae of low pathogenicity for animals; 35% of these strains possessed moderate virulence for guinea-pigs, 30% low virulence and 35% were non-virulent.(2) Prolonged nasal discharge after moderately severe diphtheria was in one case associated with a strain of B. diphtheriae which was non-virulent for guinea-pigs.(3) Acid production in various carbohydrate media proved a valuable means of differentiating diphtheria-like bacilli, but the exact composition of the medium is of importance. Peptone water appears to be especially suitable for the basis as being least liable to variation.(4) The agglutination test gave a fairly uniform result with most of the strains of virulent B. diphtheriae, but three virulent strains did not give a decided positive reaction to this test. Of the non-virulent strains half gave a slight, the remainder a negative result.Bacillus pseudo-diphtheriae (Hofmann) and certain acid producing diphtheroids gave no reaction.(5) B. fusiformis and spirochaetes occurred in large numbers on the fauces in this epidemic of diphtheria, in association with the B. diphtheriae.(6) After all the boys had received prophylactic infections of antitoxin and after the carriers had been isolated the epidemic promptly ceased.I have to thank Lieut.-Col. Sir Joseph Fayrer, Medical Officer of the Duke of York's School, who was at the time Acting Commandant, for his permission to publish this account.I am very much indebted to Dr Boycott and Dr Marshall for the very large amount of help which they gave me, and to Dr Dean for his assistance throughout the investigation.