What is the most important nursing intervention to prevent the spread of infection in a healthcare setting?

Hand hygiene is THE single most effective infection prevention measure — repeatedly documented in research. WHO's 5 Moments of Hand Hygiene: (1) BEFORE touching a patient; (2) BEFORE clean/aseptic procedure; (3) AFTER body fluid exposure risk; (4) AFTER touching a patient; (5) AFTER touching patient surroundings. Method: (1) Soap and water for visibly soiled hands, after restroom, after contact with C. difficile or known spore-forming organisms, before eating; wet hands, soap, rub all surfaces 20 seconds (palms, backs, between fingers, fingertips, thumbs, wrists), rinse, dry with paper towel, turn off faucet with towel; (2) Alcohol-based sanitizer (60%+ alcohol) for non-visibly-soiled hands — apply enough to cover all surfaces, rub until dry (~20 seconds); FASTER and often MORE EFFECTIVE than soap/water for non-soiled hands, but NOT effective against C. diff, norovirus (use soap/water instead). Common errors: (1) Skipping moments (especially between patients in a shared room); (2) Inadequate technique (too brief, missing fingertips and thumbs); (3) Recontaminating after washing (touching dirty surfaces, using bare hand to turn off faucet); (4) Skipping when gloves are worn (gloves are NOT a substitute for hand hygiene — perform hand hygiene before donning and after removing gloves). Gloves: appropriate for body fluid risk but not always — overuse wastes resources and can paradoxically increase contamination if not changed between tasks. Sterile technique: only required for sterile procedures (urinary catheterization, central line dressing changes, surgery, etc.) — not for routine care. PPE escalates with transmission risk.