After any prolonged shutdown, whether it is annual shutdown, holidays or the COVID-19 lockdown, buildings have idle water systems that are stagnating and risk fostering the growth of Legionella, the bacteria that causes Legionnaires’ Disease.
The BBC has reported three schools in the UK will delay opening because Legionella has been identified. Here is the link:
It is no surprise, the extended holiday / lockdown means the building water systems have been idle allowing water to stagnant, providing an environment for the growth of bacteria. If the water systems have not been flushed, the water system needs to be assessed.