Clinical Report: Legionella Antibody Prevalence in Northeastern Australia Blood Donors 2016-2023

Overview

This study analyzed 1001 plasma samples from blood donors in Northeastern Australia collected in 2016 and 2023 to assess Legionella antibody seroprevalence. While overall seroprevalence remained stable (~32%), there was a significant decrease in L. pneumophila antibodies and a concurrent increase in L. longbeachae antibodies. Associations were found between L. pneumophila seropositivity and environmental factors such as rainfall and land cover.

Background

Legionella species, particularly L. pneumophila and L. longbeachae, are important causes of legionellosis, which ranges from mild Pontiac fever to severe pneumonia known as Legionnaires’ disease. L. pneumophila commonly colonizes water systems, while L. longbeachae is associated with soil and potting mix. Increases in legionellosis cases were observed in Queensland, Australia during 2021–2022, mainly due to L. longbeachae. Understanding seroprevalence and environmental risk factors is critical for public health surveillance and prevention.

Data Highlights

Key Findings

• Total Legionella antibody seroprevalence remained stable between 2016 (32.46%) and 2023 (32.28%).
• Significant decrease in L. pneumophila serogroups 1–6 from 19% to 13% (P = .0182) and serogroups 7–14 from 24% to 18% (P = .0257).
• Significant increase in L. longbeachae seropositivity from 1% to 3% (P = .0355).
• L. pneumophila seroprevalence positively correlated with higher rainfall and specific land cover types, including croplands and urban areas.
• Demographic factors such as age and gender were analyzed but environmental factors showed stronger associations with seropositivity.
• Findings highlight the importance of monitoring Legionella exposure risks, especially in vulnerable populations like the elderly and immunocompromised.

Clinical Implications

Clinicians should be aware of the shifting epidemiology of Legionella species, with increasing L. longbeachae exposure in Northeastern Australia. Environmental factors such as rainfall and land use should be considered when assessing patient risk for legionellosis. Preventive measures and heightened surveillance in high-risk areas can help protect vulnerable individuals from severe disease.

Conclusion

While overall Legionella antibody prevalence remained stable over seven years, the species distribution shifted, with decreased L. pneumophila and increased L. longbeachae seropositivity. Environmental factors play a significant role in exposure risk, underscoring the need for targeted public health strategies.

References

1. Queensland Health 2021-2022 -- Increase in Legionnaire's Disease Cases
2. Graham et al. 2017 -- Global Legionella Seroprevalence Estimates
3. Australian Red Cross Lifeblood -- Blood Donor Sample Source
4. National Notifiable Disease Surveillance System Australia 2022 -- Legionella Notifications