Legionella pneumophila pneumonia in South Eastern Sydney: diagnosis, prognosis and public health outcomes

BACKGROUND: Legionellosis causes more severe disease than other aetiologies of community-acquired pneumonia (CAP). Early recognition and treatment of Legionella pneumonia reduce mortality. Urinary antigen testing (UAT) has facilitated rapid and reliable diagnosis of Legionella pneumonia. AIMS: The aims of this study were as follows: (i) identify characteristics of CAP patients more likely to be associated with a positive Legionella UAT, (ii) identify clinical features of Legionella pneumonia associated with higher risk of intensive care unit (ICU) admission and (iii) describe public health interventions resulting from positive Legionella UATs. METHODS: We conducted a case-control study of CAP patients admitted at two South-Eastern Sydney hospitals between January 2015 and March 2024 who underwent Legionella UAT. Multivariable logistic regression was used to identify characteristics associated with a positive Legionella UAT and ICU admission. RESULTS: There were 13 697 Legionella UATs during the study period, and 51 (0.4%) were positive. A total of 100% of the Legionella UAT-positive cases could be detected by conducting Legionella UAT in CAP patients with at least one of the following characteristics: >20 standard alcoholic drinks/week, confusion, failure of outpatient antibiotic therapy, diarrhoea, myalgias, temperature >40°C, serum sodium 300 mg/L. CURB-65 score, CRP and heart rate were independent factors associated with ICU admission. Positive Legionella UAT results led to 11 regulatory actions under the Public Health Act. CONCLUSION: Our study identified characteristics of CAP patients more likely to be associated with a positive Legionella UAT. Future prospective studies with greater power and in different populations may assist in refining this model to create a clinical decision-making tool to determine the appropriateness of Legionella UAT in CAP.