Why are males more susceptible to Legionellosis?

Males are consistently reported to have a higher incidence of Legionnaires’ disease than females — typically 2–3 times higher. This is due to a combination of behavioural, biological, and environmental factors:

1. Higher exposure risk

• More likely to work in high-risk environments (cooling towers, construction, water systems)
• Greater exposure to aerosolised water sources
• Higher rates of smoking, which damages lung defence mechanisms

2. Pre-existing health conditions

• Increased prevalence of:
  • Chronic lung disease (e.g. COPD)
  • Cardiovascular disease
  • Alcohol-related illness
    These reduce the body’s ability to fight infection.

3. Biological / immune differences

• Hormonal effects:
  • Oestrogen may enhance immune response
  • Testosterone may suppress aspects of immunity
• Females generally mount a stronger immune response, aiding bacterial clearance

4. Lung capacity (possible contributing factor)

• Males typically have larger lung volumes than females
• This may result in:
  • Slightly greater inhalation of aerosolised particles during exposure
• However, this is considered a secondary factor, and evidence is limited compared to other risks

5. Health-seeking behaviour

• Men are more likely to:
  • Delay seeking medical attention
  • Present with more advanced disease

Bottom line

The increased risk in males is mainly driven by:

• Exposure
• Lifestyle factors (especially smoking)
• Underlying health conditions
• Immune differences

Lung capacity may play a small role, but it is not a primary driver of increased susceptibility.