BMC Infect Dis. 2018 Jan 25;18(1):53. doi: 10.1186/s12879-018-2968-1.

A complex scenario of tuberculosis transmission is revealed through genetic and epidemiological surveys in Porto.

Rito T^1,², Matos C³, Carvalho C^4,⁵, Machado H^6,⁷, Rodrigues G⁴, Oliveira O⁸, Ferreira E³, Gonçalves J⁹, Maio L³, Morais C¹⁰, Ramos H¹¹, Guimarães JT^8,^12,¹³, Santos CL^6,⁷, Duarte R^8,^14,¹⁵, Correia-Neves M^6,⁷.

Author information

1: Life and Health Sciences Research Institute (ICVS), School of Medicine, University of Minho, Gualtar Campus, 4710-057, Braga, Portugal. teresarito@med.uminho.pt.
2: ICVS/3B's, PT Government Associate Laboratory, Braga/4805-017, 4710-057, Guimarães, Portugal. teresarito@med.uminho.pt.
3: Eastern Porto Public Health Unit, (ACES Porto Oriental), 4200-510, Porto, Portugal.
4: Northern Health Regional Administration, Department of Public Health, 4000-078, Porto, Portugal.
5: Multidisciplinary Unit for Biomedical Research (UMIB), Institute of Biomedical Sciences Abel Salazar, University of Porto, 4050-013, Porto, Portugal.
6: Life and Health Sciences Research Institute (ICVS), School of Medicine, University of Minho, Gualtar Campus, 4710-057, Braga, Portugal.
7: ICVS/3B's, PT Government Associate Laboratory, Braga/4805-017, 4710-057, Guimarães, Portugal.
8: EPI Unit, Institute of Public Health, University of Porto, 4050-600, Porto, Portugal.
9: Western Porto Public Health Unit, (ACES Porto Ocidental), 4100-503, Porto, Portugal.
10: Porto TB Outpatient Centre, Centro Diagnóstico pneumológico, 4250-162, Porto, Portugal.
11: Porto Hospital Centre, Hospital Santo António, 4099-001, Porto, Portugal.
12: Clinical Pathology, São João Hospital Centre, 4200-319, Porto, Portugal.
13: Biomedicine Department, Faculty of Medicine, University of Porto, 4200-319, Porto, Portugal.
14: Pulmonology Department, Centro Hospitalar de Vila Nova de Gaia/Espinho EPE, 4400-129, Vila Nova de Gaia, Portugal.
15: Clinical Epidemiology, Predictive Medicine and Public Health Department, Faculty of Medicine, University of Porto, 4200-319, Porto, Portugal.

Abstract

BACKGROUND:

Tuberculosis (TB) incidence is decreasing worldwide and eradication is becoming plausible. In low-incidence countries, intervention on migrant populations is considered one of the most important strategies for elimination. However, such measures are inappropriate in European areas where TB is largely endemic, such as Porto in Portugal. We aim to understand transmission chains in Porto through a genetic characterization of Mycobacterium tuberculosis strains and through a detailed epidemiological evaluation of cases.

METHODS:

We genotyped the M. tuberculosis strains using the MIRU-VNTR system. We performed an evolutionary reconstruction of the genotypes with median networks, used in this context for the first time. TB cases from a period of two years were evaluated combining genetic, epidemiological and georeferencing information.

RESULTS:

The data reveal a unique complex scenario in Porto where the autochthonous population acts as a genetic reservoir of M. tuberculosis diversity with discreet episodes of transmission, mostly undetected using classical epidemiology alone.

CONCLUSIONS:

Although control policies have been successful in decreasing incidence in Porto, the discerned complexity suggests that, for elimination to be a realistic goal, strategies need to be adjusted and coupled with a continuous genetic characterization of strains and detailed epidemiological evaluation, in order to successfully identify and interrupt transmission chains.