Usefulness of 3'- 5' IS6110-RFLP genotyping and spoligotyping of Mycobacterium tuberculosis isolated in a tertiary hospital: a retrospective study detecting unsuspected epidemiological events

A drug resistance survey involving Mycobacterium tuberculosis isolated from patients of a tertiary Hospital in the Rio de Janeiro city (RJ), Brazil, between the years 1996 and 1998 revealed a high frequency of isoniazid (HR) resistance. These isolates were revisited and genotyped. Patients came from different RJ neighborhoods and municipalities, and 70% were outpatients. Applying the 3' and 5' IS 6110 -RFLP and the Spoligotype genotyping methods, the clonal structure of this population was investigated obtaining a snapshot of past epidemiological events. The 3' clusters were subsequently 5' IS 6110 -RFLP typed. Spoligotyping was analyzed in the SITVIT2 database. Epidemiological relationships were investigated. The major lineage was T (54.4%), and SIT 53/T1 and SIT 535/T1 were the most frequent. The T1 sublineage comprises 12.8% of resistant strains and SIT 535 were assigned for 31.8% of them. Orphan patterns corresponded to 12% and 73.3% and belonged to the T lineage. One pattern was unlisted in the SITVIT2. The 5' IS 6110 -RFLP did not confirm 3/12 of the 3' IS 6110 -RFLP clusters. A combination of all methods decreased the number of clusters to three. Nosocomial transmission was associated with one cluster involving a hospital cupbearer. This event was suspected in a multidrug resistant-TB inpatient caregiver who harbored a mixed infection. The 3' IS 6110 clusters were associated with HR (p=0.046). These genotypic retrospective data may reflect a fraction of more extensive recent transmission in different communities that may be corroborated by the concentration of HR patients, and may serve as a database for further evolutionary and characterization evaluation of circulating strains and together with epidemiological data favors a more effective transmission control.