From the CDC website:

Introduction
Influenza is a common cause of respiratory illness requiring outpatient health-care visits and hospitalization. During the influenza season, outbreaks of health-care-associated influenza affect both patients and personnel in chronic care facilities and hospitals. This document provides infection control guidance for prevention and control of influenza transmission in health-care facilities.
Transmission
Influenza transmission occurs predominantly by large respiratory droplets (particles >5 µ in diameter) that are expelled from the respiratory tract during coughing or sneezing. Particles usually do not remain suspended in the air, and close contact (<3 feet) usually is required for transmission. Transmission also occurs through direct contact with respiratory droplets or secretions, followed by touching the nose or mouth.
Prevention and Control Measures
Strategies for the prevention and control of influenza in health-care facilities include the following: influenza immunization for persons at high risk for complications, immunization for health-care workers, Respiratory Hygiene/ Cough Etiquette programs, Standard Precautions and Droplet Precautions, and visitor and worker restrictions.

Read more about the flu, it’s prevention and signs/symptoms at the CDC site.