We spend our lives surrounded by (and carrying with us internally and on our skin) bacteria, fungi, algae viruses and other forms of microscopic life. Microbes comprise 80-90% of the Earth's total biomass, and even under 'clean' conditions we may inhale several thousand fungal spores per day. Many, fortunately, are harmless or even useful (think of penicillin, yoghurt, bread, beer and wine yeasts) but others can be lethal or severely disabling.
We increasingly eat food produced thousands of miles away, transported for an extended period, prepared in bulk or at restaurants and takeaways; work in air-conditioned offices, attend large hospitals in which infections can spread rapidly, expect to travel from one country to another at high speed and short notice.
Methods used to keep the levels of this nanolife down to acceptable levels have traditionally included the use of easily cleaned surfaces such as tiles, vitreous enamel and stainless steel, persistent biocides and strong cleaning agents.