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The following is a summary of “Clinical and epidemiological characteristics of Legionnaires’ disease in Southern Sweden, a population-based study,” published in the April 2025 issue of Infectious Diseases by Wikén et al. 

Researchers conducted a retrospective study to describe diagnosed cases of Legionnaire’s disease (LD), focusing on incidence, characteristics, diagnostics, outcomes, and infection control investigations.  

They analyzed data from individuals with LD in Skåne between 2011–2021. Inclusion required a positive polymerase chain reaction (PCR) for Legionella pneumophila/Legionella spp. or a positive urinary antigen test (UAT), along with clinical symptoms consistent with Legionella infection and radiological confirmation of pulmonary infiltrates.  

The results showed that 280 individuals met the inclusion criteria, with a mean incidence of 2.00 per 1,00,000 person-years (95% CI: 1.23–2.78). Empiric treatment covering Legionella was administered in 15% of cases. Mortality rates were 13% at 30 days, 15% at 90 days, and 23% at 365 days, UAT was conducted in 88% of cases, with a 66% positivity rate. Lower respiratory tract PCR was performed in 76% of cases, yielding a 90% positivity rate. Bacterial culture was positive in 43% of cases, with L. pneumophila serogroup 1 being the most common (58%), while serogroups 2–14, undetected by UAT, accounted for 30%. Genetic matches between environmental and patient strains were confirmed in 5% of cases.  

Investigators concluded that LD was clinically significant but often treated with inappropriate initial antibiotics, and diagnosis required PCR on lower respiratory samples in addition to UAT, while environmental sources were usually identified but rarely definitively linked to infection. 

Source: tandfonline.com/doi/full/10.1080/23744235.2025.2476532