Why is Legionnaires’ disease more common in men than women?

Introduction

Legionnaires’ disease is a potentially fatal respiratory illness caused by Legionella bacteria which leads to pneumonia. Everyone is susceptible to contracting Legionnaires’ disease although some individuals hold an increased susceptibility. The Health and Safety Executive provides a background overview of the illness and symptoms on its website. Susceptibility plays a big role in Legionnaires’ disease infections with over 80% of cases reported in England and Wales between 2017 and 2023 having at least one condition which increased the patients’ susceptibility (Source: gov.uk).

Legionnaires’ disease affects males at a significantly higher rate than females, with around 70% of all recorded cases typically occurring in males. For example, in 2023 604 cases of Legionnaires’ disease were reported in England and Wales with 70.2% (424 cases) of those cases reported in males (Source: gov.uk). This trend is often attributed to men being more likely to work in an environment where they could be exposed to Legionella bacteria but this often feels too simplistic as an explanation. Furthermore, workplaces and society in general have changed significantly in recent years and with trends such as a 6% increase in females working in engineering between 2010 and 2022 (Source: Institution of Mechanical Engineers) we might expect to see a change in the ratio of Legionnaires’ disease cases reported in males, although the reported figures do not indicate any significant change to support this theory.

Analysis

The reality is that multiple factors increase an individual’s risk of contracting Legionnaires’ disease, making the reason males are more likely to contract the illness a lot more complex than simply place of work. Below we summarise these points.

Hormonal and Immune System Differences:

Testosterone has been identified as having a link to a weakened immune response (Source: Stanford Medicine news centre), potentially increasing the susceptibility of males to infection. Furthermore oestrogen has been linked to a stronger immune response (Source: MDPI), potentially reducing the susceptibility of females to infection. Studies have shown that the trend of increased rates of infection in males is not unique to Legionnaires’ disease and that this trend is noted in many infectious diseases, which seems to support these points (Source: NIH).

Smoking Rates:

Smoking damages the lungs and increases an individual’s susceptibility to respiratory infections, including Legionnaires’ disease. In the UK in 2023 males were confirmed to be more likely to smoke than females with 13.7% of men and 10.1% of women smokers (Source: gov.uk). The higher instance of smoking among males creates a greater proportion of males with an increased susceptibility to Legionella infections than their female counterparts.

Occupational Exposure:

Men are more likely to work in industries such as construction, plumbing, building maintenance and industrial settings where there is often an increased risk of exposure to Legionella bacteria. Occupational exposure is often noted as a risk factor including in official UK government data (Source: Public Health England).

Healthcare-Seeking Behaviour:

Women tend to seek medical care sooner than men, leading to earlier detection and treatment of infections, which may reduce the likelihood of progression to severe disease like Legionnaires’ disease. While perhaps more anecdotal, there are scientific studies which support this theory, including the following articles;

Underlying Health Conditions:

Chronic conditions like diabetes, alcoholism, heart conditions and many lung diseases which increase the susceptibility of an individual to Legionnaires’ disease are more prevalent in men than women (Source: NIH), which creates an increased number of males with a higher susceptibility to Legionella infection than females.

Summary

The sex-based trend for greater case numbers of Legionnaires’ disease in males compared to females is not unique to Legionnaires’ disease itself but actually a trend seen in multiple infectious diseases. It does seem reasonable to deduce that more males than females contract Legionnaires’ disease as a result of their working environment but to give this as the over-arching cause for the trend is too simplistic. The reasons for the significant difference in case numbers between men and women are much more complex and multi-factorial, with aspects ranging from behaviour to hormonal and immune system differences between the sexes.