Transmission of tuberculosis in Havana, Cuba: a molecular epidemiological study by IS6110 restriction fragment length polymorphism typing

The combination of molecular and conventional epidemiological methods has i mproved the knowledge about the transmission of tuberculosis in urban popul ations. To examine transmission of tuberculosis in Havana, Cuba, with DNA f ingerprinting, we studied 51 out of 92 Mycobacterium tuberculosis strains i solated from tuberculosis patients who resided in Havana and whose infectio n was culture-confirmed in the period from September 1997 to March 1998. Is olates from 28 patients (55%) had unique IS6110 restriction fragment length polymorphism (RFLP) patterns, while isolates from 23 others (45%) had iden tical patterns and belonged to 7 clusters. Three clusters consisting of six , five and two cases were each related to small outbreaks that occurred in a closed setting. Thr-ee other clustered cases were linked to a large outbr eak that occurred in another institution. Younger patients where more corre lated to clustering than older ones. The finding that 45% of the isolates h ad clustered RFLP patterns suggests that recent transmission is a key facto r in the tuberculosis cases in Havana. The IS6110 RFLP typing made it possi ble to define the occurrence of outbreaks in two closed institutions.