Last December the ECDC reported on a cluster of MDR-TB among a group of 16 migrants who had recently entered the EU during the first six months of 2016 (see Multidrug-resistant tuberculosis in migrants, multi-country cluster, first update 19 Dec 2016).
By the end of March, the ECDC reported that cluster had grown to 25 cases (see ECDC: Rapid Risk Assessment On Multi-Country Cluster Of MDR-TB In Migrants), where they stated:
A WGS analysis of the 25 cluster isolates supports the hypothesis that the cases are part of a chain of recent transmission likely to have taken place either in the country of origin or in a place along the migration route to the country of destination. Based on the currently available information, it is not possible as of yet to rule out that transmission occurred in an EU/EFTA country.
It therefore remains important to rapidly investigate exposure risk factors, including the travel history and itineraries of patients and their contacts, and share this information to determine whether transmission may have taken place in the EU/EFTA, during migration, or in the country of origin. Depending on the results of the investigation, appropriate prevention and control measures should be taken.
Today the ECDC has published an interim report on that epidemiological investigation, which expands the cluster to 28 cases, attempts to document the travel history of these cases and their contacts, and updates their Rapid Risk Assessment for the EU.
I've only posted some limited excerpts from the 7-page epidemiological report. Follow the link below to read it in its entirety.
Multidrug-resistant tuberculosis in migrants, multi-country cluster
Third update, 13 April 2017
Conclusions and options for response
A multi-country cluster of multidrug-resistant tuberculosis (MDR TB) involving 28 migrants has been delineated by whole genome sequencing (WGS).
In December 2016, Switzerland initially reported a cluster of seven MDR TB cases to the European Commission in newly-arrived migrants from Somalia (5 cases), Eritrea (1 case) and Ethiopia (1 case). The Commission then informed the Member States through an Early Warning and Response System (EWRS) message. Following the EWRS notification, Germany, Austria, Finland, France and Sweden reported cases that were linked to this cluster on the basis of WGS. Switzerland later reported an eighth case. As of 4 April 2017, isolates from 28 cases that are part of the WGS cluster had been reported from Germany (14), Switzerland (8), Austria (2), France (2), Finland (1) and Sweden (1). All cases have a recent history of migration from Somalia (23), Eritrea (3), Sudan (1) and Ethiopia (1).
The six countries involved in the multi-country cluster have implemented migrant screening.
Early case identification of active TB and drug susceptibility testing, especially in migrants arriving from the Horn of Africa, is important in order to identify and treat active cases and provide preventive treatment or monitoring for those diagnosed with latent tuberculosis infection .
It is therefore important to rapidly investigate exposure risk factors, including the travel history and itineraries of patients and their contacts, and share this information to determine whether transmission may have taken place in the EU/EEA, during migration, or in the country of origin. Depending on the results of the investigation, appropriate prevention and control measures should be taken.
Although the number of cases detected so far suggests that there is only a limited risk of this cluster becoming a widespread event in Europe, more cases associated with this cluster may yet be identified
ECDC threat assessment for the EU
Twenty-three of the twenty-eight cases in this cluster have an epidemiological link with Somalia, although Somalis represent only 2.1% of the refugee population in the EU/EEA according to the International Organization for Migration (IOM). The three remaining cluster cases had travelled along the same migration route. No cases associated with other migration routes to the EU have been identified in relation to this cluster, suggesting that transmission took place in the country of origin or along the migration route prior to entering the EU/EEA.
The clustering of case strains by WGS within one SNP difference suggests that transmission was recent and likely to have taken place either in the patients’ country of origin or in a place along their migration route to the country of destination. For three of the 20 documented cases, infection clearly occurred while in the Horn of Africa, prior to migration. However, for other cases, infection may have occurred during migration, in particular in Libya for migrants who spent a long time there in unsanitary conditions (e.g. Bani Walid). It is possible that some transmissions occurred in Europe, but the likelihood is low, given the intense efforts to identify cases and the short travelling times and better living conditions for migrants in Europe compared to those during migration.
Infected persons who do not have active TB are not infectious. However, they are at risk of developing active TB disease and becoming infectious. The lifetime risk of reactivation TB for a person with documented latent TB infection is estimated to be 5 to 10%, with the majority developing TB disease within the first five years of initial infection .
The risk of transmission within the EU/EEA is primarily within the affected migrant population, but a low risk of transmission to the indigenous population cannot be ignored. This risk is low because TB incidence in a foreign-born population does not have a significant influence on the overall TB incidence in the indigenous population. Therefore, while there remains a risk of additional cases being detected among newly-arrived migrants, the risk of transmission to the EU/EEA population is considered low.