External quality assessment schemes to support European surveillance of Legionnaires’ disease in Western Balkan countries, 2022–2023

This report describes the external quality assessment (EQA) scheme for the European Legionnaires’ disease Surveillance network, for the detection, isolation, identification, and enumeration of Legionella species. The EQA schemes provide an outbreak scenario with packages of clinical and environmental samples for the participating laboratories to process, according to their technical capacity and protocols. The purpose of the 2022–2023 EQA exercise was to continue monitoring the accuracy of Legionella testing and results reported by individual laboratories and to enable comparison of results between laboratories and within countries across Europe. This report presents an analysis of the results for Western Balkan countries. It also includes results from a survey on the methods/kit information and frequency of testing performed for each method/kit, which was sent to all participating laboratories. A total of six Western Balkan countries were invited to take part via their national ECDC correspondents for Legionnaires’ disease. A maximum of two laboratories per country were selected, based on their involvement in surveillance and the management of public health incidents associated with Legionella in their country. The samples for the 2022–2023 exercise were sent in April 2023. Each package contained 10 samples representing clinical material (distribution 5582) and 10 samples containing environmental material (distribution 5581). Strains of Legionella were provided by the Respiratory and Vaccine Preventable Bacteria Reference Unit (RVPBRU) of the United Kingdom Health Security Agency (UKHSA) and these strains were fully characterised using conventional and molecular methods. Laboratories only needed to examine the samples they would routinely test or process and report whether any contained a Legionella spp., and then provide identification, enumeration levels, serogroup (Sg) and sequence type (ST), where relevant. This exercise represented an outbreak associated with a dental practice. The outbreak strain of Legionella pneumophila Sg 1, ST2681 was isolated from clinical specimens and environmental samples. This sequence type of L. pneumophila is rare and has only been identified in the UK five times since 2018. It has the following allelic profile: 6,10,2,10,13,4,9 and is a single-locus variant of ST501, ST969 and ST2110.