"Classical" and "Asian" variants of Mycobacterium tuberculosis isolated in South East England 1977-1980.

Strains of Mycobacterium tuberculosis were divided into 'classical' and 'Asian' types according to their susceptibility to thiophen-2-carboxylic acid hydrazide (TCH). A study of 6638 new cases of tuberculosis showed that there was a much higher incidence of non-pulmonary disease among Asian than among European patients, and that the TCH-sensitive 'Asian' type of organism was much commoner among the former. There was, however, no correlation between the site of disease and the type of organism. Resistance to antituberculosis drugs was more frequent among strains from Asian patients but there was no correlation between such resistance and susceptibility to TCH. No evidence was therefore found to link differences in the clinical features of tuberculosis in the two populations of patients to the type to organism.