International Journal of Biometeorology

, Volume 62, Issue 7, pp 1167–1179 | Cite as

The unprecedented 2014 Legionnaires’ disease outbreak in Portugal: atmospheric driving mechanisms

  • Ana Russo
  • Célia M. Gouveia
  • Pedro M. M. Soares
  • Rita M. Cardoso
  • Manuel T. Mendes
  • Ricardo M. Trigo
Original Paper


A large outbreak of Legionnaires’ disease occurred in November 2014 nearby Lisbon, Portugal. This epidemic infected 377 individuals by the Legionella pneumophila bacteria, resulting in 14 deaths. The primary source of transmission was contaminated aerosolized water which, when inhaled, lead to atypical pneumonia. The unseasonably warm temperatures during October 2014 may have played a role in the proliferation of Legionella species in cooling tower systems. The episode was further exacerbated by high relative humidity and a thermal inversion which limited the bacterial dispersion. Here, we analyze if the Legionella outbreak event occurred during a situation of extreme potential recirculation and/or stagnation characteristics. In order to achieve this goal, the Allwine and Whiteman approach was applied for a hindcast simulation covering the affected area during a near 20-year long period (1989–2007) and then for an independent period covering the 2014 event (15 October to 13 November 2014). The results regarding the average daily critical transport indices for the 1989–2007 period clearly indicate that the airshed is prone to stagnation as these events have a dominant presence through most of the study period (42%), relatively to the occurrence of recirculation (18%) and ventilation (17%) events. However, the year of 2014 represents an exceptional year when compared to the 1989–2007 period, with 53 and 33% of the days being classified as under stagnation and recirculation conditions, respectively.


Legionnaires’ disease Outbreak Recirculation Stagnation Weather Research and Forecasting (WRF) model Regional climate simulation 



The authors would like to acknowledge the European Centre for Medium Weather Forecast for providing the meteorological data. The authors gratefully acknowledge the NOAA Air Resources Laboratory (ARL) for the provision of the HYSPLIT transport and dispersion model and/or READY website ( used in this publication. Pedro M.M. Soares and Rita M. Cardoso thank the Portuguese Science Foundation (FCT) for funding under Project SOLAR-PTDC/GEOMET/7078/2014. Ana Russo also thanks FCT by the research grant SFRH/BPD/99757/2014.

Supplementary material

484_2018_1520_MOESM1_ESM.docx (274 kb)
ESM 1 (DOCX 274 kb)


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Copyright information

© ISB 2018

Authors and Affiliations

  1. 1.Instituto Dom LuizFaculdade de Ciências da Universidade de LisboaLisbonPortugal
  2. 2.Instituto Português do Mar e da AtmosferaLisbonPortugal

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