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Open Access Research article

Genotypic characteristics of Mycobacterium tuberculosis isolated from household contacts of tuberculosis patients in the Philippines

Irene G Sia6, Seanne P Buckwalter1, Kelly A Doerr1, Sonia Lugos2, Rebecca Kramer2, Ruth Orillaza-Chi3, Maria Imelda Quelapio4, Thelma E Tupasi45 and Nancy L Wengenack1*

Author Affiliations

1 Department of Laboratory Medicine and Pathology, Mayo Clinic, 200 First Street SW, Rochester, MN 55905, USA

2 Michigan Department of Community Health, Lansing, Michigan, USA

3 University of the Philippines and Philippine General Hospital, Manila, The Philippines

4 Tropical Disease Foundation, Manila, The Philippines

5 Makati Medical Center, Manila, The Philippines

6 Division of Infectious Diseases, Mayo Clinic, 200 First Street SW, Rochester, MN 55905, USA

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BMC Infectious Diseases 2013, 13:571  doi:10.1186/1471-2334-13-571

Published: 5 December 2013

Abstract

Background

The Philippines has an extremely high rate of tuberculosis but little is known about M. tuberculosis genotypes and transmission dynamics in this country. The aim of this study was to determine the proportion of household contacts who develop active TB due to direct transmission from an index case in that household.

Methods

Mycobacterium tuberculosis isolates from household contacts of tuberculosis patients in the Philippines were characterized using restriction-fragment-length polymorphism analysis, spoligotyping, and mycobacterial interspersed repetitive units – variable number tandem repeats typing (12-loci) to determine their utility in elucidating transmission in an area of high tuberculosis prevalence. Drug susceptibility patterns for these isolates were also determined.

Results

Spoligotyping and MIRU-VNTR typing results matched in 10 (62.5%) of 16 index patient-household contact pairs while IS6110 fingerprints matched in only six (37.5%) pairs. Only 3/16 (18.8%) index patient-household contact pairs had identical drug susceptibility results.

Conclusions

Strain typing of M. tuberculosis isolates from household contacts in the Philippines indicates that transmission of strains does not necessarily occur directly from the index patient living in close proximity in the same household but rather that community-based transmission also frequently occurs. Accurate susceptibility testing of all isolates is necessary to insure optimal care of both the index patients and any culture-positive household contacts.