Hospital-acquired pneumonia overview

# Overview
Hospital-acquired pneumonia (HAP) or nosocomial pneumonia refers to any pneumonia contracted by a patient in a hospital at least 4872 hours after being admitted. It is thus distinguished from community-acquired pneumonia. It is usually caused by a bacterial infection, rather than a virus.  HAP is the second most common nosocomial infection (after urinary tract infections ) and accounts for 1520% of the total. It is the most common cause of death among nosocomial infections and is the primary cause of death in intensive care units.  HAP typically lengthens a hospital stay by 12 weeks.

# Pathophysiology
Most nosocomial respiratory infections are caused by so-called skorvatch 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.

# Causes
The majority of cases related to various gram-negative bacilli (52%) and S. aureus (19%). Others are Haemophilusspp. (5%). In the ICU results were S. aureus(17.4%), P. aeruginosa (17.4%), Klebsiella pneumoniae andEnterobacter spp. (18.1%), and Haemophilus influenzae (4.9%). Viruses -influenza and respiratory syncytial virus and, in the immunocompromised host, cytomegalovirus- cause 10-20% of infections.

# Differentiating Hospital-Acquired Pneumonia From Other Diseases
Hospital-acquired pneumonia must be differentiated from other conditions that cause fever, cough, chest pain, tachycardia, and leukocytosis in hospitalized patients, such as atelectasis, congestive heart failure, pulmonary embolism, aspiration pneumonitis, among others. 

# Epidemiology and Demographics
The epidemiology of health-care-associated pneumonia varies considerably according to the type of health-care setting. Nosocomial pneumonia has been the second most common hospital-associated infection after that of the urinary tract. The primary risk factor for the development of hospital-associated bacterial pneumonia is mechanical ventilation.  In long-term care facilities such as nursing homes, pneumonia is the first or second most common infection (after those of the urinary tract) acquired by patients, and accounts for 13-48% of all nursing home-associated infections. 

# Risk Factors
Among the factors contributing to contracting HAP are mechanical ventilation (ventilator-associated pneumonia), old age, decreased filtration of inspired air, intrinsic respiratory, neurologic, or other disease states that result in respiratory tract obstruction, trauma, (abdominal) surgery, medications, diminished lung volumes, or decreased clearance of secretions may diminish the defenses of the lung.  Also poor hand-washing and inadequate disinfection of respiratory devicescauses cross-infection and is an important factor.

# Natural History, Complications, and Prognosis
The natural history of HAP depends on many factors and occurs 48 hours or more after hospitalization. Complications include sepsis, respiratory failure, pleural effusion, empyema, and lung abscess.  Healthcare-associated pneumonia seems to have fatality rates similar to hospital-acquired pneumonia, worse than community-acquired pneumonia but less severe than pneumonia in ventilated patients.  Besides clinical markers like tachypnea (fast breathing) or a high white cell count (leukocytosis), the prognosis seems to be influenced by the underlying associated diseases (comorbidities) and functional capacities. Many patients have a decreased health condition after the episode.

# Diagnosis

## Diagnostic Criteria
In hospitalised patient who develop respiratory symptoms and fever one should consider the diagnosis.  The likelyhood 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 ofpleural effusion thoracentesis is performed for examination of pleural fluid.  In suspected ventilator-associated pneumonia it has been suggested that bronchoscopy(BAL) is necessary because of the known risks surrounding clinical diagnoses.

## History and Symptoms
People with pneumonia often have a productive cough, fevershaking chills, shortness of breath, pleuritic chest pain, hemoptysis, headaches, sweaty, and clammy skin. Other possible symptoms are loss of appetite, fatigue, cyanosis, nausea, vomiting, mood swings, and joint pains or muscle aches. In elderly people manifestations of pneumonia may not be typical. They may develop a new or worsening confusion or may experience unsteadiness, leading to falls. Infants with pneumonia may have many of the symptoms above, but in many cases they are simply sleepy or have a decreased appetite. In VAP, often no history is available in patients with ventilator-associated pneumonia as they are often sedated and are rarely able to communicate.

## Physical Examination
Physical examination is important in diagnosing  hospital-acquired pneumonia, finding include fever, tachypnea, rhonchi, crackles and wheezes.  For ventilator-associated pneumonia, a deterioration in ventilator parameters such as, tachypnea, decreased tidal volume, increased minute ventilation, or decreased oxygen saturation could be the first indicators of a new onset ventilator-associated pneumonia.

## Laboratory Findings
Current guidelines recommend a combination of chest X-ray, laboratory data as well as clinical judgment in diagnosis and management of community acquired pneumonia.  Laboratory tests include CBC, metabolic panel, sputum gram-stain and culture, serology for mycoplasma, chlamydia, and legionella.  Additional test include bronchial samples and HIV testing for special conditions.

## Chest X-ray
An important test for making a diagnosis of pneumonia is a chest x-ray. Chest x-rays can reveal areas of opacity (seen as white) which represent consolidation, pleural effusion, air bronchogram and/or cavitations. Pneumonia is not always seen on x-rays, either because the disease is only in its initial stages, or because it involves a part of the lung not easily seen by x-ray.

# Treatment

## Medical Therapy
The medical regimen in patients with hospital-acquired pneumonia will depend on the risk factors and the likelihood of drug resistance pathogens. For patients with no risk factors for MDR pathogens, the regimen consists of one antibiotic medication, usually ceftriaxone or a fluoroquinolone.   For patients with risk of MDR pathogens, a three drug combination regimen is preferred; which includes an antipseudomonal cephalosporin or carbapenem plus a fluoroquinolone plus linezolid or vancomycin (for MRSA coverage).

## Prevention
The prevention for HAP includes education of health-care workers about the epidemiology and infection-control procedures, and involve the workers in the implementation of interventions to prevent HAP by using performance-improvement tools and technique.  Disinfection and maintenance of equipment and devices, as well as preventive measures of person to person transmission, are part of the preventive recommendations given by the CDC for HAP.

## Cost-Effectiveness of Therapy
Linezolid was compared to vancomycin for the treatment of VAP, and showed cost-effectiveness as an alternative to vancomycin treatment as it had a higher cure rate and prices per treatment were similar.  One study reported that oropharingeal decontamination decreased the incidence of ventilator-associated pneumonia from 4% to less than 1% in the studied population. The cost of the intervention was less than $2500.