16 months between Portuguese Listeria outbreak start and detection

Listeriosis is a notifiable disease in Portugal, but active surveillance is just starting.

The first reported foodborne listeriosis outbreak in Portugal highlights the need for an effective surveillance system for early detection and prompt submission of isolates for typing, according to researchers. The number of cases between March 2009 and February 2012 was 30 with a fatality rate of 36.7%. Cheese was the probable source of infection, found the report in Eurosurveillance.

The long duration of this outbreak, (March 2009 to February 2012) linked with queijo fresco (fresh cheese) is noteworthy and reinforces the importance of setting up an effective multidisciplinary team able to help ensure rapid notification of cases and the prompt submission of L. monocytogenes isolates for routine laboratory typing.

 A retrospective study involving 25 national hospitals led to the awareness of the outbreak, meaning the time between the presumed onset and its detection was 16 months. Notifiable disease but no active surveillance In Portugal, listeriosis has been notifiable since April 2014, but there is no active surveillance program. As there is no such program, outbreak detection is extremely difficult and work on the one reported was due mainly to retrospective investigations.

Between January and July 2010, a high number of listeriosis cases was observed (40 compared with 20 during all of 2009) particularly in the Lisbon and Vale do Tejo region.

Molecular typing of the 40 L. monocytogenes clinical isolates revealed 18 serotype IVb isolates presented the same PFGE type and ribotype observed for five isolates recovered in 2009. Continued monitoring detected two more cases with the outbreak strain in November 2010, three more in January, February and March 2011 and two in February 2012.

Processing plant investigation: The food safety authority inspected 42 food retailers and collected 103 samples for analysis (51 meat products, 24 dairy products, 13 ready­ to­ eat foods and 15 environmental swabs). L. monocytogenes was found in four samples collected at a retailer: three from queijo fresco and one from a swab from a ham slicing­machine; one queijo fresco sample contained Listeria counts greater than 100 CFU/g.

PFGE typing revealed isolates recovered from two queijo fresco samples of different brands from the same retailer showed the same PFGE type as the clinical isolates with the outbreak strain.  

In European countries with established surveillance programs, such as France, Germany and the UK, the incidence of listeriosis is reported to be increasing and the distribution of cases is shifting, primarily affecting elderly persons and those with predisposing medical conditions, leading to a high case fatality rate.

Source: http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=21104