Evidence of transmission of tuberculosis by DNA fingerprinting

Abstract

Objective: To determine whether a subject who had died of tuberculous meningitis had been infected by a neighbour.

Design: Retrospective comparison of isolates of Mycobacterium tuberculosis from the two cases and from 10 controls by DNA fingerprinting.

Setting: Public Health Service Reference Laboratory for Mycobacteria and bacterial molecular genetics unit of the London School of Hygiene and Tropical Medicine.

Subjects: Deceased and neighbour; 10 controls from the same city, from whom isolates had been collected over three months before the subject's death.

Main outcome measures: Identity and similarity values (SAB) between fingerprint patterns from different isolates obtained by hybridisation of restriction fragments produced by PvuII with a probe from the insertion element IS6110/986, present in multiple copies throughout the genome of M tuberculosis.

Results: Isolates from the two cases under investigation had identical fingerprints whereas those from the controls were all distinct. Two clusters of isolates with a similarity coefficient > 0.25 were identified: in one, four out of five patients were born in the midlands (the birth place of the fifth was not known) and in the other all three patients were born in the Indian subcontinent.

Conclusions: The data are consistent with, but do not prove, transmission of tuberculosis from the neighbour to the deceased. Geographical separation of the pools of infection may have led to the evolution of distinct clusters of fingerprint patterns. DNA fingerprinting of M tuberculosis is a powerful new tool for study of the epidemiology and pathogenesis of tuberculosis.