History and exam
Key diagnostic factors
common
presence of risk factors
Risk factors include non-municipal water supply, recent residential plumbing repair, smoking, use of whirlpool spas, and living close to a cooling tower.
known acquaintance with Legionella
Signifies potential outbreak.
fever
Pulse/temperature dissociation may be present.[42]
headache
May be prominent symptom.[42]
crackles/rhonchi
Legionnaires' disease only, not Pontiac fever.[42]
Other diagnostic factors
common
productive cough
Typical symptom.
dyspnoea
Typical symptom.
nausea/vomiting
May be present.
abdominal pain
May be present.
hypoxia
Typical signs of pneumonia may be present.
tachycardia
Typical signs of pneumonia may be present.
Risk factors
strong
non-municipal water supply
Multivariate analysis: odds ratio, 2.26; 95% CI, 1.17 to 4.37.[18]
The cleaning process that is conducted at water treatment plants kills Legionella.
recent residential plumbing repair
Multivariate analysis: odds ratio, 2.39; 95% CI, 1.10 to 5.18.[18]
An interruption in the water line stops flow, changes water temperature, and allows air and possibly Legionella to enter.
smoking
use of whirlpool spas
living close to a cooling tower
Cooling towers are frequently colonised with Legionella. While most people exposed will not develop the disease, contaminated towers increase the risk of transmission.[26]
weak
cytotoxic chemotherapy
Multivariate analysis: odds ratio, 5.2; 95% CI, 1.5 to 17.9.[20]
In one study, anti-tumour necrosis factor (TNF) alpha inhibitors including infliximab, adalimumab, and etanercept were associated with legionellosis.[21] The overall annual incidence rate for Legionella in those receiving a TNF-alpha inhibitor was 46.7 (95% CI, 0.0 to 125.7) per 100,000 patient-years.
Immunosuppression predisposes to nosocomial-acquired Legionella pneumonia.
lung transplant recipient
Two patients acquired Legionnaires' disease who had recently received a lung transplant from the same donor. The transplanted lungs were the most likely source of infection as the donor had drowned in a freshwater river and hospital water quality tests were within normal ranges. Three additional recipients who received the heart, liver, and right kidney from the same donor did not develop complications suggestive of legionellosis.[22]
corticosteroids
electric water heater
Univariate analysis: odds ratio, 1.97; 95% CI, 1.10 to 3.52.[18]
Electric water heaters are more likely than gas water heaters to harbor infection due to lower water temperatures. Lower temperatures are more favourable for growth and propagation of Legionella.
working >40 hours per week
Univariate analysis: odds ratio, 2.13; 95% CI, 1.12 to 4.07.[18]
Time away from home, including travel, may be associated with Legionnaires' disease.
recent travel
Univariate analysis: odds ratio, 1.68; 95% CI, 1.03 to 2.74.[18][19]
Travel may expose people to infectious aerosols, particularly when staying in hotels with poorly maintained decorative fountains, outdated plumbing systems, and contaminated heating/cooling devices. Approximately 10% of all reported cases of Legionnaires’ disease in the US occur in people who have travelled in the 10 days prior to symptom onset.[10]
diabetes mellitus
Having a chronic disease that may be associated with immunosuppression and lead to frequent admissions to hospital may predispose to Legionnaires' disease.[19]
professional driver
Drivers are exposed to multiple water sources and multiple other travellers who are a higher-risk population.[19]
filling nebuliser, humidifiers, ventilator tubing, or lavage equipment with tap water
Anecdotal reports of outbreaks.[27]
close proximity to a decorative fountain
Anecdotal report of an outbreak.[28]
consumption of Legionella pneumophila-contaminated ice
Consumption of Legionella-contaminated ice may confer risk for infection due to the possibility of micro-aspiration.[29]
delivery by water birth
exposure to contaminated compost
Legionella in compost may become airborne when opening packages.[32]
exposure to rainwater
Exposure to rainwater has been shown to be associated with Legionella.[33]
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