My theory was a simple one - I'd read about how antibiotics were actually contributing to the degradation of the human immune system and how some doctors had begun to inject house dust and dirt into children?s bloodstreams in an effort to strengthen nature's own defenses again. I liked that idea as a metaphor for the state of apathy, fear and violence - which has gripped America and Britain in particular - and used it to construct this story. The Filth is an attempt to 'inject' into my readers a healing concoction of vile ideas, hurtful emotions and unacceptable images.