Epidemiologic usefulness of spoligotyping for secondary typing of Mycobacterium tuberculosis isolates with low copy numbers of IS6110

Restriction fragment length polymorphism (RFLP) analysis of IS6110 is commo nly used to DNA fingerprint Mycobacterium tuberculosis. However, low-copy ( less than or equal to5) IS6110 M. tuberculosis strains are poorly different iated, requiring secondary typing. When spoligotyping was used as the secon dary method, only 13% of Maryland culture-positive tuberculosis (TB) patien ts with low-copy IS6110-spoligotyped clustered strains had epidemiologic li nkages to another patient, compared to 48% of those with high-copy strains clustered by IS6110 alone (P < 0.01). Spoligotyping did not improve a popul ation-based molecular epidemiologic study of recent TB transmission.