The increasing health burden of Legionella Pneumophila in NSW.

Background: Legionella pneumophila can cause severe respiratory disease and is notifiable in NSW. An analysis of notifications linked to hospitalisation and death data over the period 2010-2022 was conducted to determine the burden of disease and any association with the introduction of NSW regulatory changes in 2018.

Methods: Cases were retrospectively identified from the Notifiable Conditions Records for Epidemiology and Surveillance (NCRES). Data on related morbidity and mortality were obtained from linked data within the NSW Communicable Disease Register (CDR). The impact of the regulatory change was evaluated by analysing monthly count data using an interrupted time series analysis.

Results: A total of 928 cases were notified with 84% admitted to hospital. Annual adjusted notification and admission rates increased over the period from 4.40 to 7.92 cases and 3.72 to 7.20 admissions, per 1,000,000 population, respectively. The mean length of hospital stay (LOS) was 14 days with a median of 8 days (range 1-262 days). Time series analysis identified an underlying increasing time trend in cases notified per month with an IRR of 1.069 (95% ci 0.751-1.523) post 2018 regulatory implementation.

Conclusion: L. pneumophila is posing an increasing burden of disease with an underlying upward trend in notification incidence despite the introduction of regulatory changes in 2018.

Implication For Public Health Practice: This study demonstrates how linking notification, hospitalisation and death data can measure the health burden of a notifiable condition. Furthermore, time-series analysis using these data is able to identify underlying temporal trends and evaluate policy changes.