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Country-wide surveillance of norovirus outbreaks in the Portuguese Army, 2015–2017
  1. António Lopes-João1,
  2. J R Mesquita2,3,
  3. R de Sousa4,
  4. M Oleastro4,
  5. C Silva4,
  6. C Penha-Gonçalves1 and
  7. M S J Nascimento3,5
  1. 1 Laboratório de Bromatologia e Defesa Biológica do Exército (LBDB), Lisboa, Portugal
  2. 2 Instituto Politécnico de Viseu – Escola Superior Agrária (ESAV), Viseu, Portugal
  3. 3 Epidemiology Research Unit (EPIUnit), Instituto de Saúde Pública da Universidade do Porto, Porto, Portugal
  4. 4 Laboratório Nacional de Referência para as Infeções Gastrointestinais, Departamento de Doenças Infecciosas, Instituto Nacional de Saúde Dr Ricardo Jorge, Lisboa, Portugal
  5. 5 Laboratório de Microbiologia, Departamento de Ciências Biológicas, Faculdade de Farmácia da Universidade do Porto, Porto, Portugal
  1. Correspondence to Professor J R Mesquita, Instituto Politecnico de Viseu, Viseu, 3504-510, Portugal; jmesquita{at}


Introduction Gastrointestinal infections are among the most common foodborne and waterborne diseases in military populations, with direct implications in operational efficiency and force readiness. Through the surveillance system of reportable acute gastrointestinal illness in the Portuguese Army, four norovirus outbreaks were identified between October 2015 and October 2017 in mainland Portugal and the Azores archipelago. The present study documents the epidemiological, clinical and laboratory investigations of these norovirus outbreaks.

Methods Cases were investigated and epidemiological questionnaires were distributed to all soldiers in each military setting where the outbreaks occurred. Stool samples from soldiers with acute gastroenteritis illness were collected and screened for common enteropathogenic agents. Food and water samples served on the settings were also collected for microbiological investigation. Norovirus-positive samples were further characterised by sequence analysis using a public automated genotyping tool.

Results The four outbreaks affected a total of 99 soldiers among the 618 stationed on base units and in a military exercise. A total of 27 soldiers provided a stool sample, of which 20 were positive for norovirus by real-time PCR. Phylogenetic analysis showed that the noroviruses involved were all genogroup II, namely GII.17, GII.Pe-GII.4 Sydney 2012, GII.P2-GII.2 and GII.P16-GII.2. Of note, 30 soldiers had to receive treatment at the military hospital due to severity of symptoms.

Conclusion In this short, two-year surveillance period, a total of four norovirus gastroenteritis outbreaks were detected in the Portuguese Army which caused a considerable morbidity, showing once again the impact of norovirus on Army effectiveness and force readiness.

  • gastrointestinal infections
  • epidemiology
  • public health

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  • Contributors AL-J, JRM, RdS, MO, CS, CP-G and MSJN equally contributed to the manuscript.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Patient consent Not required.

  • Provenance and peer review Not commissioned; externally peer reviewed.