Legionellosis

Legionellosis is the infection caused by bacteria of the genus Legionella, and it includes a non-pneumonic influenza-like syndrome as well as Legionnaires’ disease, the more serious pneumonic illness ^[1]. Legionnaires’ disease is described as a severe pneumonia and systemic infection caused by Legionella bacteria ^[2]. The condition has been recognised since its first identification in early 1977 ^[2].

The clinical spectrum ranges from a non-pneumonic influenza-like syndrome to Legionnaires’ disease, which is characterized by pneumonia and systemic involvement ^[1][2]. In severe disease, the clinical picture may include marked lung injury requiring respiratory and/or hemodynamic support, extrapulmonary symptoms, and non-specific laboratory findings ^[3]. The disease is described as non-specific in presentation, which contributes to it being overlooked clinically ^[2]. Severe cases may require intensive care, and the reported mortality range in the source literature is broad ^[3].

Legionella is recognised as a common cause of community-acquired pneumonia and a rare cause of hospital-acquired pneumonia ^[2]. The condition is increasingly important as a public-health problem worldwide, although it remains underreported; studies cited in the source material describe high incidence and rising overall occurrence ^[1][3]. Severe disease is particularly noted among patients with risk factors, especially immunosuppression, and the source literature also identifies age and underlying debilitating conditions as susceptibility factors ^[2][3]. Legionella is associated with outbreaks, and notification systems are described as important for initiating investigations and limiting recurrence ^[2].

The major natural reservoir for Legionella is water, and the organism is found in both natural and artificial aquatic environments, including cooling towers and building water systems, hospitals included ^[2]. The provided sources do not further specify the exact route of human acquisition beyond this water-associated exposure ecology. Source-backed detail on persistence, infective dose, or person-to-person spread is not yet available in the supplied material.

The sources identify susceptible patients as those affected by older age, underlying debilitating conditions, or immunosuppression ^[2]. Severe outcomes are reported more often in immunocompromised patients and in cases with a nosocomial source ^[3]. Beyond these groups, source-backed detail on additional high-risk populations is not yet available in the supplied material.

Prevention in the supplied sources centers on environmental control of water-associated sources and outbreak limitation through surveillance and notification ^[2]. Because Legionella is linked to cooling towers and building water systems, including hospitals, exposure control in these settings is implied by the described reservoir ecology ^[2]. Source-backed detail on specific engineering standards, disinfection protocols, or population-based preventive schedules is not yet available in the supplied material.

Legionellosis should be read in surveillance as an underreported but increasingly recognized cause of pneumonia, with particular relevance to severe community-acquired disease and nosocomial settings ^[1][2]. The source literature emphasizes that notification systems are essential for outbreak investigation and for limiting scale and recurrence ^[2]. Ongoing monitoring is also important because improved diagnostic methods may increase case detection over time ^[1][3].

1. 1 Viasus D et al. Legionnaires' Disease: Update on Diagnosis and Treatment. Infect Dis Ther. 2022 Jun. PMID: 35505000. doi: 10.1007/s40121-022-00635-7. PubMed: https://pubmed.ncbi.nlm.nih.gov/35505000/
2. 2 Cunha BA et al. Legionnaires' disease. Lancet. 2016 Jan 23. PMID: 26231463. doi: 10.1016/S0140-6736(15)60078-2. PubMed: https://pubmed.ncbi.nlm.nih.gov/26231463/
3. 3 Rello J et al. Severe Legionnaires' disease. Ann Intensive Care. 2024 Apr 2. PMID: 38565811. doi: 10.1186/s13613-024-01252-y. PubMed: https://pubmed.ncbi.nlm.nih.gov/38565811/
4. 4 Legionellosis. Van Nostrand's Scientific Encyclopedia. 2005. doi: 10.1002/0471743984.vse4530. DOI: https://doi.org/10.1002/0471743984.vse4530
5. 5 Legionellosis. Antimicrobics and Infectious Diseases Newsletter. 1997. doi: 10.1016/s1069-417x(00)80033-3. DOI: https://doi.org/10.1016/s1069-417x(00)80033-3
6. 6 Legionellosis. Tropical Infectious Diseases. 2006. doi: 10.1016/b978-0-443-06668-9.50038-7. DOI: https://doi.org/10.1016/b978-0-443-06668-9.50038-7

ICD-10

ICD-11

Total cases

98K

Peak month

2023-01

Coverage

8 reporting countries · 2000-01-01 → 2026-06-20