Abstract
BackgroundTuberculosis (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.MethodsWe 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.ResultsThe 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.ConclusionsAlthough 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.
Highlights
Tuberculosis (TB) incidence is decreasing worldwide and eradication is becoming plausible
61.8% of the samples collected were isolated from individuals registered as living in the city of Porto, whereas 38.2% were from individuals registered as living in the surroundings of the city
There is over a decade of valuable MIRU genotyping data that when analysed with other tools could provide further insights into modelling and understanding of transmissibility and outbreaks
Summary
Tuberculosis (TB) incidence is decreasing worldwide and eradication is becoming plausible. Intervention on migrant populations is considered one of the most important strategies for elimination Such measures are inappropriate in European areas where TB is largely endemic, such as Porto in Portugal. Tuberculosis (TB) still ranks as one of the deadliest infectious diseases worldwide [1] It has been consistently declining in Europe, some urban areas still display a high incidence [2]. This is the case for the city of Porto in Portugal where, in 2014, the reported incidence rate was 46.3 cases per 100,000 inhabitants [3] This higher incidence in European urban areas has been associated with disproportionately affected sub-populations, In the TB-endemic Porto urban area, there has been a continuous reduction of TB incidence from 81 to 38 cases per 100,000 people in one decade (2002–2012) [7], Rito et al BMC Infectious Diseases (2018) 18:53 leading to a very recent shift from relatively high to intermediate TB incidence. The Porto urban area could potentially be a useful model with which to study and develop control strategies in European endemic urban areas
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