Nosocomial pneumonia or hospital-acquired pneumonia (HAP) is defined as pneumonia that occurs 48 hours or more after hospital admission and not incubating at the admission time. Ventilator-associated pneumonia (VAP) represents a significant sub-set of HAP occurring in intensive care units (ICUs) and is defined as pneumonia that occurs more than 48 to 72 hours after tracheal intubation and is thought to affect 10% to 20% patients receiving mechanical ventilation for more than 48 hours.
Common pathogens of HAP and VAP include aerobic gram-negative bacilli (e.g. Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumoniae, Enterobacter spp, Acinetobacter spp) and gram-positive cocci (e.g., Staphylococcus aureus, which includes methicillin-resistant S. aureus, Streptococcus spp). Differences in host factors and in the hospital flora of an institution affect the patterns of the causative pathogens.
Risk Factors for multidrug-Resistant (MDR) VAP
Risk Factors for MDR HAP
Risk Factors for MRSA VAP/HAP
Risk Factors for MDR Pseudomonas VAP/HAP
Symptoms may include cough, expectoration, a rise in body temperature, chest pain or dyspnea. Signs include fever, tachypnea, consolidations or crackles.
Establishing the diagnosis of HAP remains controversial, and there is no superior method. In the guidelines for the management of HAP and VAP by Infectious Diseases Society of America/American Thoracic Society 2016, diagnosis is based upon a presence of new lung infiltrate and clinical evidence that the infiltrate is of an infectious cause (new onset of fever, purulent sputum, leukocytosis, and a decline in oxygenation). Clinical pulmonary infection score (CPIS), which includes clinical and radiological criteria, is suggested to increase the likelihood of the presence of pneumonia, but some investigators suggest that the CPIS while being sensitive, lacks specificity and leads to unnecessary antimicrobial treatment 
For patients with VAP sampling the lower airways to get quantitative cultures can be done by:
For patients with HAP (non-VAP), noninvasive methods for sampling the lower airways include spontaneous expectoration, sputum induction, nasotracheal suctioning in a patient who cannot cooperate to produce a sputum sample.
All respiratory tract samples should be sent for microscopic analysis and culture.
The microscopic analysis includes the analysis of polymorphonuclear leukocytes and a gram stain. The microscopy can be helpful in determining a possible pathogen and the antibiotic selection until the results of the culture are available. The presence of abundant neutrophils and the bacterial morphology may suggest a likely pathogen.
Diagnostic thresholds include:
New Molecular Diagnostic Tests
New molecular diagnostic tests like multiplex polymerase chain reaction assay, which detects an array of respiratory bacterial pathogens and many antibiotic resistance genes, offer the advantage of rapid identification of pathogens and resistance patterns for rapid choosing the antibiotic regimens.
Initial empiric therapy for HAP and VAP should include agents active against Staphylococcus aureus, Pseudomonas aeruginosa, and other gram-negative bacilli. The choice of antibiotics for empiric therapy should be based on the common pathogens and susceptibility patterns within the health care facilities and also based on the patient's risk factors for multidrug resistance.
All patients with HAP or VAP should be reevaluated for clinical response and the microbiologic results after initial empiric antimicrobial therapy.
Duration of antibiotic therapy in most patients with HAP or VAP of 7 days appears to be as effective as longer durations and may limit the emergence of a resistant organisms. However, for patients with a severe illness, bacteremia, slow response to therapy, immunocompromise, and complications such as empyema or lung abscess, a longer duration of therapy is indicated.
Many studies have found that HAP is associated with an increased risk of death. The all-cause mortality associated with VAP ranges from 20% to 50% in different studies. Variables associated with increased mortality include:
Managing hospital-acquired pneumonia (HAP) and ventilator-associated pneumonia (VAP) requires an interprofessional team of specialists in infectious diseases, pulmonary diseases, critical care, anesthesiologists, and any clinicians and healthcare providers including nurses and pharmacists caring for hospitalized patients with nosocomial pneumonia. Without proper management the morbidity and mortality from HAP and VAP are high. (Level II)