The typical presentation of an atypical pathogen during an outbreak of Legionnaires’ disease in Vila Franca de Xira, Portugal, 2014

Abstract Background An outbreak of Legionella pneumophila serogroup 1, with 403 cases was identified on the 7th November 2014 in Vila Franca de Xira, Portugal. Outbreak source was the wet cooling system of a local factory. Hospital Pulido Valente was one of the hospitals receiving patients with Legionnaires’ disease (LD). Methods We describe the clinical findings and diagnostic methods used among the 43 confirmed or probable cases admitted to our department. Results 60.5% were male, mean age was 56.1 ± 13.5 years and tobacco smoking was the most frequent risk factor (76.7%). All patients had fever, 62.8% ≥39.5 °C, 72.1% had chills and myalgia/arthralgia and 62.8% had dry cough. Extra pulmonary symptoms were frequent: confusion and headache occurred in 34.9% and gastrointestinal symptoms in 20.9%. High C-Reactive Protein (55.8% ≥30 mg/dL) and hyponatremia (62.8%) were the laboratorial abnormalities most commonly found. Hypoxemia occurred in 55.8% and hypocapnia in 93%. Urinary Antigen Test (UAT) was positive in 83.7% of the cases. Conclusions Although not specific, a combination of risk factors, symptoms and laboratory findings can be highly suggestive of LD, even in an outbreak. This should prompt diagnosis confirmation. Routine use of UAT in less severe cases of community acquired pneumonia might contribute to earlier diagnosis.