Its risk factors include patients with mechanical ventilation, cystic fibrosis, debilitation, impaired immune responses intravenous drug abuse and multiple administering of antibacterial drugs. Contaminated disinfection solutions, nebulizers, and topical anesthetics have been associated with sporadic outbreaks of the bacterial disease. Sporadic outbreaks of the infection have been noted in ICU and burn unit. Non-fermenting gram-negative bacteria with a rod shape. The predisposing factors for infection or colonization are: central venous catheters. mechanical ventilation. ICU location. invasive devices. organ transplant. immunosuppressed patients. neutropenia. cytotoxic chemotherapy. prior antibiotic therapy. tracheotomies. The bacteria can be isolated the surrounding such as ventilator tubing, suction equivalent, water sources, spirometers, disinfecting solutions, hospital sinks and nebulizers. The two most common microorganisms associated with ventilator-associated pneumonia and other healthcare associated pneumonia (HAP). The pathogens can arise secondary to environmental surrounding rather than from the patients indigenous flora. Legionella growth is optimal at temperatures between 25° and 42°. Legionella species is found mostly aquatic environments. Legionella has also been isolated from evaporative condensers, cooling towers and heat portable water distribution systems. Transmission occurs through inhalation of aerosols. Prevention of ventilator-associated pneumonia focuses on reducing the risk of aspiration.