Ian, it is a real risk if water has been sitting there for that amount of time in a house temperature. My advice is not to let your wife anywhere near the shower room. If you can remove the shower head and run the hot water for as long as you can at the hottest temperature from the hose - bit of an issue if it is on a mixer - so if you can turn off the cold water feed. It is the advice given if you visit a hotel at the start of a season abroad!!! The risk is mainly from aerosol - so avoid the situation where the shower is hitting a surface causing a spray. I would do this before the plumber comes as he may be dismissive of your issue - surprisingly many are very ignorant of legionella. I dont think there are any chemicals you can use that you get domestically - but the microbiologists will advise

The "slug" of water in the dead-leg up to the shower needs to be run-off, but it matters not what temperature you do it at. Presumably the soleniod valve is inoperable on your (electric) shower, preventing you running the system cold at regular intervals? Something we all need to be aware of when going on holiday too - that shower. toilet or tap in the apartment may not have been operated all winter long.

And if you don't have a bucket handy on holiday try tieing a carrier bag around the shower attachment and then turn on shower slowly so it fills gently and when full carefully drain down the plug creating as little splash as possible. Then order for the shower (least susceptible to most susceptible) is children, followed women and then men last (unless you have any smokers - who should go last of all). From a talk I heard given by a Dr Lee of the HPA some years ago.

The risk of legionellosis to your wife is virtually nil unless she is immune-compromised and she is inhaling spray containing legionella. Regards.

This is quite an interesting thread, and to be truthful quite an eye opener, I would never have thought that the first person using a shower in a hotel or holiday park at the beginning of the season would be in such danger? I honestly would have thought that the owners of these establishments would ask their cleaning staff to clean each bathroom before their first clients of the year arrived. However I do believe that the information put on by several previous posters must be correct. Shocking, I will always from now on be really careful with showers in other properties!

Thanks for the information everyone - I'll make sure the plumber knows and will ensure that splash is minimised (for anyone that's interested, if you switch the shower on, nothing comes out of the head, it just runs straight out the bottom of the unit!) This is our first child, so no young daughter I could send in - it's nice to know it's an option for ther future though!!! Thanks once again.

No joke, true, but didn't say I would use it, but then again not being CMIOSH (don't know what CMIOSH has to do with it) obviosly a very clever person. Nooooo I'm not starting the CMIOSH arguement again.