Clinical and epidemiological characteristics of Legionnaires' disease in Southern Sweden, a population-based study.

BACKGROUND

The study aimed to describe all diagnosed cases of Legionnaire's disease (LD) in south Sweden, regarding incidence, patient characteristics, diagnostics, outcomes, and infection control investigations.

METHODS

This population-based retrospective study was conducted in Skåne, on patients with LD between 2011-2021. Inclusion criteria were positive polymerase chain reaction (PCR) for L. pneumophila/Legionella spp. or a positive urinary antigen test (UAT), combined with a clinical presentation consistent with Legionella infection and radiological evidence of pulmonary infiltrates.

RESULTS

A total of 280 patients met the inclusion criteria, with a mean incidence of 2.00 per 100,000 person-years (95% CI: 1.23-2.78). Empiric treatment covering Legionella was administered in 15% of cases. Mortality rates were 13%, 15% and 23% at 30-, 90- and 365 days, respectively. UAT was performed in 88% of patients, with a 66% positivity rate. Lower respiratory tract PCR was performed in 76% of patients with a 90% positivity rate. Bacterial culture was positive in 43% of cases. Out of these, L. pneumophila serogroup 1 was most common (58%), though a significant proportion were serogroups 2-14 (30%), which are not generally detected by UAT. Genetic matches between environmental and patient strains were established in 5% of cases.

CONCLUSION

Legionnaires' disease in Skåne is an uncommon but clinically significant condition. Few patients received appropriate empiric antibiotic treatment. Reliance on UAT alone is insufficient for establishing diagnosis, and species-specific PCR, particularly from lower respiratory samples, enhances detection. Environmental investigations frequently identified Legionella in suspected settings; however, a definitive source of infection was rarely established.