**Core Concept**
Nosocomial infections, also known as hospital-acquired infections, are infections that patients acquire during the course of receiving treatment for other conditions in a healthcare setting. Preventing nosocomial infections is crucial to reduce morbidity, mortality, and healthcare costs. Effective infection control measures involve a combination of hand hygiene, proper use of personal protective equipment (PPE), and environmental cleaning.

**Why the Correct Answer is Right**
The correct answer emphasizes the importance of hand hygiene in preventing nosocomial infections. Hand hygiene is the single most effective measure to prevent the spread of infections in healthcare settings. The World Health Organization (WHO) recommends the "5 moments for hand hygiene" approach, which includes hand hygiene before and after touching patients, before and after inserting invasive medical devices, and after exposure to bodily fluids. Hand hygiene should be performed using either soap and water or an alcohol-based hand rub.

**Why Each Wrong Option is Incorrect**
**Option A:** Other options like improving ventilation and air filtration are also important for infection control, but they are not the best way to prevent nosocomial infections.
**Option B:** Although proper use of PPE is essential, it is not the most effective measure to prevent nosocomial infections.
**Option C:** Environmental cleaning is crucial for infection control, but it is not the best way to prevent nosocomial infections.

**Clinical Pearl / High-Yield Fact**
Hand hygiene should be performed for at least 20 seconds to ensure effective removal of microorganisms. Using an alcohol-based hand rub is more effective than washing with soap and water in reducing the transmission of infections.

**Correct Answer: A. Hand hygiene is the best way to prevent nosocomial infections.**