Comparing Legionnaires’ Disease & COVID-19: Identifying Similarities & Differences
This article compares both the similarities and differences between Legionnaires’ disease and COVID-19. Taken from data collected in May 2020 the article looks at the early symptoms of both infections and how they compare, who seems to be most at risk, routes to transmission; and the possible impact of geography, local environmental conditions and temperature on rates of infection.
Comparing Legionnaires’ Disease and COVID-19
A recent preprint report written by Andrew John Pendery in May 2020 looked at the similarities between Legionnaires’ disease and COVID-19.
The coronavirus has swept across the world in mere months, causing devastating changes for many people and countries.
While it is too early to say if Mr Pendery’s report has merit, it is well referenced and is convincing when highlighting certain similarities between the two diseases.
It should, however, be noted that the report is a hypothesis.
It takes information from various sources and uses this to highlight areas where similarities can be noted.
Early symptoms of both Legionnaires’ and COVID-19
For example, the initial symptoms an infected person presents with are similar for both conditions:
- Dry cough (this develops into a productive one for Legionnaires’ disease)
- A fever
Other possible symptoms for both include gastrointestinal issues, although these do not always present with COVID-19.
Similarly, muscle aches are highlighted in the report, but again, do not always present with both conditions.
The most at-risk age group for both Legionnaires’ and COVID-19 is the elderly
Those aged 45 and over are at greater risk of contracting Legionnaires’ disease according to information gleaned from the UK’s Health and Safety Executive (HSE).
The risk of being affected increases as we age, and the same has been seen to be true with the statistics we now have concerning COVID-19 victims.
Other similarities between the two include:
- Men being at greater risk
- Many of those who die presented with one or more other conditions (i.e. Chronic obstructive pulmonary disease (COPD), diabetes, etc.)
- Cases that progress to become more serious present with symptoms akin to pneumonia
Since both Legionnaires’ disease and the coronavirus affect the lungs and can cause pneumonia, it would make sense that similarities could be identified.
What about “Sticky blood syndrome”?
It’s worth mentioning that the two conditions are different and are caused by different things.
For starters, COVID-19 is a virus while legionella is a bacterium.
We are also beginning to realise that COVID-19 results in blood clots – the so-called sticky blood syndrome – in some more seriously-affected individuals.
It is surmised that the way the body fights the infection causes the blood to become sticky.
Levels of a marker called D-dimer are under 300 in normal individuals.
Someone who has had a stroke might expect their levels to go up to around 1,000.
But one COVID-19 patient (who has made a remarkable recovery) had levels of 80,000+ when he was tested.
Clearly, this is not something we see in those with Legionnaires’ disease.
However, there are other areas the report dives into that do see similarities between the two.
Geographical and environmental factors affecting Legionnaires’ and Coronavirus
Many outbreaks of Legionnaires’ disease occur in places that are used by lots of people… we’ve seen outbreaks in hotels and hospitals, for example.
One similarity we can highlight here is that COVID-19 appears to be more easily spread when lots of people are present in the same place.
Social distancing has become part of all our lives in recent months and for good reason.
Staying away from people who may potentially be infected reduces our chances of contracting the disease.
The method of becoming ill differs between the two illnesses, however.
COVID-19 is contagious, hence why we are told to socially distance ourselves from others.
People can be contagious before they even present with symptoms.
In contrast, Legionnaires’ disease is not thought to be contagious.
People who develop the disease do so after inhaling infected droplets of water from contaminated sources that can include cooling towers, spa pools and showers.
The more people are exposed to that source, the higher the infection rate is likely to be.
So, while certain locations may potentially present greater risks, the method of transmission is different between the two.
(Post report update – Many scientists, including those at the WHO have recently acknowledged there is emerging evidence that the coronavirus can be spread by tiny particles suspended in the air)
The report went on to compare geographical regions to see if there were similarities in where the cases of these diseases cropped up… this made for interesting reading.
It highlighted that New York State in the USA was one of the hardest hit regions in the country for both Legionnaires’ infections and COVID-19 infections.
Quite why that is the case remains unknown.
It could be a statistical anomaly or coincidence.
High population density might also be a factor, yet other areas of the USA with high populations don’t seem to be affected the same way.
Similarly, Italy was one of the hardest hit countries in Europe during the pandemic.
It also reported one of the highest levels of Legionnaires’ disease occurrences during 2017.
However, again, this pattern doesn’t apply across the board.
The UK has suffered many deaths during the pandemic, yet it is one of the lowest countries on numbers for reported Legionnaires’ disease infections.
Does environmental temperature influence the odds of getting each disease?
It’s still early days when it comes to learning more about this coronavirus, how it affects the body, whether there are any long-term issues caused by it, and how many people are severely affected.
We know far more about Legionnaires’ disease to be sure – but we have had many more years to understand it compared to COVID-19.
One area where clear differences seem to be emerging concerns the season where each disease appears to have the greatest impact.
Since we are only a few months into the pandemic, forthcoming months should provide more information on this.
However, so far, it appears that warmer climates could help suppress the coronavirus, while colder weather may allow it to proliferate.
Respiratory infections typically peak during winter in the UK and other similar climates.
This could see a drop in infections during the summer before a resurgence becomes possible in the autumn and beyond.
With Legionnaires’ disease though, cases tend to rise during the warmer months.
Legionella bacteria reproduces readily during the ideal temperature range of 20-45 degrees Celsius, making this an obvious breeding ground that puts more people at risk.
In conclusion
Mr Pendery makes some fascinating and notable points in his preprint report and it is certainly worth reading.
We have much yet to learn about this coronavirus and the progression of the pandemic in the UK and around the world.
Seeing similarities between at-risk groups of people and areas where Legionnaires’ disease and COVID-19 are prominent is easy to do.
Yet it may not mean there are clear links to make between them.
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