Legionella Risk Assessments can be done by landlords and their plumbers without any need for expensive training courses!
Plumbers who have done their NVQ qualification will have had basic instruction in college about Legionella, as it is a disease mainly associated with "outbreaks" from commercial/public and industrial plumbing systems, where large quantities of water are stored and the plumbing systems are complex. The bacteria live in rivers and lakes and can sometimes get into the water supply and multiply with the right conditions.
Isolated cases are rarely recognised or reported, simply because most cases are very mild (cough and flu-like symptoms, called Pontiac fever) and are brushed-off as being "just a bug" or "a virus". If you went to your GP he would most likely say you had a chest infection and give you some antibiotics.
It tends to be people who are already immuno-compromised in some way, such as the elderly, who become really ill and eventually are tested and diagnosed. The disease is named after some elderly American Legionnaires who became ill with pneumonia from contaminated water in a hotel where they were having a convention in the 1970's. Of course the disease existed "forever" BEFORE that, but that particular outbreak eventually identified the bacteria and gave it a name.
Nowadays if a few people in the same place become really ill and Legionella is identified, doctors start calling it "an outbreak", so they then start testing for it in everyone who presents with similar symptoms, and pretty soon the media are calling it an epidemic. There was an outbreak from some cooling towers (the most common source) in Edinburgh in 2012 when several people died. The resulting court case has dragged on since 2012 and illustrates just how difficult it is to apportion "blame".
Once you've had Legionella you develop antibodies to it and it is estimated at least 2-3% of the general population in the UK have the antibodies, so must have been in contact with Legionella at some point in their lives, it's just that they were never diagnosed. (Interestingly, in parts of Australia it's thought to be 20-30% of the population!).
Landlords of normal domestic properties have very little to worry about, especially if there is no stored water at the property (ie:- if it's a combi boiler). In ANY type of system the best advice is to run all your taps for 10-20 minutes after the system hasn't been used for a few days. Fresh chlorinated water will then enter the system pipes (and any tanks), and flush everything out. Anything which "sprays" water droplets, such as shower heads, should be descaled and disinfected, especially if the property has been empty for some time.
It really makes me a bit cross (grrrr..!!) when I read that people are running expensive training courses and then charging hefty fees just to do basic plumbing checks and write a report.
Any decent plumber will give you a "risk assessment" and check all the plumbing whilst they are at it. Cold tanks should have lids and be insulated to keep water cold; Hot cylinders should store water at or above 60 degrees, "dead-legs" (redundant pipework) should be eliminated, etc. This is all good plumbing practice anyway and is designed to prevent not only Legionella but E.Coli and MRSA (not to mention dead pigeons, squirrels, bats and rats....).
Now I've had my rant, I hope that's helpful guys an gals. Get yourselves a good plumber and all will be well.
PS:- Yes I am a plumber, but back in the 1980's I was a nurse! So please forgive my little soapbox indulgence....