Wash and scrub in a mild bleach or fungicide solution and rinse well. Air dry thoroughly preferably in sunshine.
The fungus will have formed in moisture in the environment - good ventilation helps to prevent it - open a window when making steam - cooking, washing or bathing. Keep kitchen and bathroom doors closed.
It will probably be nothing to do with the rain - just the internal environment of the house.
You can buy a cheap humidity meter at a garden centre - 40% to 70% relative humidity is usually acceptable.
Good luck...
Peccavi, March 2011
