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Contribution title Uncover the increase of reported legionellosis cases in Switzerland
  1. Fabienne Fischer Swiss Tropical and Public Health Institute, / University of Basel, Basel, Switzerland Presenter
  2. Claudia Schmutz Swiss Tropical and Public Health Institute, / University of Basel
  3. Apolline Saucy Swiss TPH / University of Basel
  4. Nicole Gysin Bundesamt für Gesundheit, BAG
  5. Daniel Mäusezahl Swiss Tropical and Public Health Institute, / University of Basel, Basel, Switzerland
Form of presentation Poster
  • Public health
Abstract Legionella spp. are common environmental bacteria living in fresh water. They are also known to cultivate in man-made water reservoirs such as cooling towers or shower heads. Infection may lead to legionellosis, a group of diseases ranging from mild Pontiac fever, pulmonary distress to potentially fatal legionnaires’ disease. In Switzerland, cases of legionellosis must be reported to the Federal Office of Public Health since 1988. Notifications were steadily rising, and more than doubled in the last 15 years.

However, increasing notifications do not necessarily reflect an actual epidemiological trend. Health seeking, testing and reporting behaviour can heavily influence these records. For legionellosis it is assumed that part of the increase can be explained by the introduction of a new urinary antigen test (UAT) around the year 2000 allowing detecting Legionella pneumophila serogroup 1 more easily and reliably than other diagnostic methods. But an expected levelling of the notification records some years after the new test has been introduced, could not be observed. Another hypothesis for the observed increase in case notifications is better awareness of practitioners for legionellosis resulting in higher case detection. Finally, the increase in case notifications could also reflect an actual increase in disease incidence.

It is essential to know if the observed increase in case numbers reflects a change in disease frequency in order to take appropriate actions. We aim to look at the proportion of positive tests out of all tests conducted, the positivity rate, for Legionella spp. Data of the last 10 years from 14 diagnostic laboratories in Switzerland will be used for analysis. Repeated tests likely belonging to the same disease episode will be excluded. Information on age, sex and canton of residence were obtained and included in the analysis to allow for standardisation and consideration of temporal - and spatial trends. Uni- and multivariable logistic regression analyses are used to test if age, sex, laboratory, test year and test method are associated with the test outcome.

This study will allow a better understanding of the surveillance data for legionellosis. Further investigation of exposure risks and possible prevention measures are needed to identify a true epidemiological trend. This includes also assessing the diagnostic approaches of physicians dealing with patients with suspected legionellosis.