Ventilator-associated pneumonia
Ventilator-associated pneumonia (VAP) is a sub-type of hospital-acquired pneumonia (HAP) which occurs in people who are receiving mechanical ventilation. VAP is not characterized by the causative agents; rather, as its name implies, definition of VAP is restricted to patients undergoing mechanical ventilation while in a hospital. A positive culture after intubation is indicative of ventilator-associated pneumonia and is diagnosed as such. In order to appropriately categorize the causative agent or mechanism it is usually recommended to obtain a culture prior to initiating mechanical ventilation as a reference. Healthcare-associated pneumonia (HCAP)
HCAP is a condition in patients who can come from the community, but have frequent contact with the healthcare environment. Historically, the etiology and prognosis of nursing home pneumonia appeared to differ from other types of community acquired pneumonia, with studies reporting a worse prognosis and higher incidence of multi drug resistant organisms as etiology agents. The definition criteria which has been used is the same as the one which has been previously used to identify bloodstream healthcare associated infections. HCAP is no longer recognized as a clinically independent entity. This is due to increasing evidence from a growing number of studies that many patients defined as having HCAP are not at high risk for MDR pathogens. As a result, 2016 IDSA guidelines removed consideration of HCAP as a separate clinical entity.
Also, poor hand-washing and inadequate disinfection of respiratory devices cause cross-infection and are important factors. Pathogenesis
Most nosocomial respiratory infections are caused by so-called microaspiration of upper airway secretions, through inapparent aspiration, into the lower respiratory tract. Also, "macroaspirations" of esophageal or gastric material is known to result in HAP. Since it results from aspiration either type is called aspiration pneumonia.Although gram-negative bacilli are a common cause they are rarely found in the respiratory tract of people without pneumonia, which has led to speculation of the mouth and throat as origin of the infection. Diagnosis
In hospitalised patients who develop respiratory symptoms and fever, one should consider the diagnosis. The likelihood increases when upon investigation symptoms are found of respiratory insufficiency, purulent secretions, newly developed infiltrate on the chest X-Ray, and increasing leucocyte count. If pneumonia is suspected material from sputum or tracheal aspirates are sent to the microbiology department for cultures. In case of pleural effusion, thoracentesis is performed for examination of pleural fluid. In suspected ventilator-associated pneumonia it has been suggested that bronchoscopy or bronchoalveolar lavage is necessary because of the risks of incorrect clinical diagnoses. Differential diagnosis
Atelectasis
Congestive heart failure
Pulmonary embolism

Treatment
Usually initial therapy is empirical. If sufficient reason to suspect influenza, one might consider oseltamivir. In case of legionellosis, erythromycin or fluoroquinolone.A third generation cephalosporin (ceftazidime) + carbapenems (imipenem) + beta lactam & beta lactamase inhibitors (piperacillin/tazobactam)

References
Further reading
Carratalà J, Garcia-Vidal C (2008). "What is healthcare-associated pneumonia and how is it managed?". Curr. Opin. Infect. Dis. 21 (2): 168–173. doi:10.1097/QCO.0b013e3282f4f248. PMID 18317041. S2CID 3060658.