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Hospital-Acquired Pneumonia


Sanjay Sethi

, MD, University at Buffalo SUNY

Last full review/revision Dec 2020| Content last modified Dec 2020

Hospital-acquired pneumonia (HAP) develops at least 48 hours after hospital admission. The most common pathogens are gram-negative bacilli and Staphylococcus aureus; antibiotic-resistant organisms are an important concern. Symptoms and signs include malaise, fever, chills, rigor, cough, dyspnea, and chest pain. Diagnosis is suspected on the basis of clinical presentation and chest x-ray and is confirmed by blood culture or bronchoscopic sampling of the lower respiratory tract. Treatment is with antibiotics. Overall prognosis is poor, due in part to comorbidities.

(See also Overview of Pneumonia.)

Hospital-acquired pneumonia includes pneumonia that was not incubating at the time of hospital admission and develops at least 48 hours after hospital admission in patients who are not receiving mechanical ventilation. Hospital-acquired pneumonia includes postoperative pneumonia but does not include patients with ventilator-associated pneumonia (VAP).

Etiology of Hospital-Acquired Pneumonia

The most common cause of hospital-acquired pneumonia is microaspiration of bacteria that colonize the oropharynx and upper airways in seriously ill patients. Seeding of the lung due to bacteremia or inhalation of contaminated aerosols (ie, airborne particles containing Legionella species, Aspergillus species, or influenza virus) are less common causes.

Risk factors

Risk factors for hospital-acquired pneumonia include previous antibiotic treatment, high gastric pH (due to stress ulcer prophylaxis or therapy with H2 blockers or proton pump inhibitors), and coexisting cardiac, pulmonary, hepatic, or renal insufficiency.

Major risk factors for postoperative pneumonia are

  • Age > 70
  • Abdominal or thoracic surgery
  • Functional debilitation


Pathogens and antibiotic resistance patterns vary significantly among institutions and can vary within institutions over short periods (eg, month to month). Local antibiograms at the institutional level that are updated on a regular basis are essential in determination of appropriate empiric antibiotic therapy. In general, the most important pathogens are

  • Enteric gram-negative bacilli, especially Pseudomonas aeruginosa
  • Gram-positive cocci, especially methicillin-sensitive Staphylococcus aureus and methicillin-resistant S. aureus (MRSA)

Other important enteric gram-negative bacteria include Enterobacter species, Klebsiella pneumoniae, Escherichia coli, Serratia marcescens, Proteus species, and Acinetobacter species).

Methicillin-sensitive S. aureus, Streptococcus pneumoniae, and Haemophilus influenzae are most commonly implicated when pneumonia develops within 4 to 7 days of hospitalization, whereas P. aeruginosa, MRSA, and enteric gram-negative organisms become more common with increasing duration of hospitalization.

Risk factors for infection with multidrug resistant (MDR) pathogens include prior intravenous antibiotic treatment (within the previous 90 days), structural lung disease, colonization with MDR pathogens, and high rates of prevalence of these pathogens in the local hospital environment. (1). Infection with a resistant organism markedly worsens mortality and morbidity.

High-dose corticosteroids increase the risk of Legionella and Pseudomonas infections. Chronic suppurative lung diseases such as cystic fibrosis and bronchiectasis increase the risk of gram-negative pathogens, including antibiotic-resistant strains.

There is increasing recognition of viruses as a cause of HAP in immunocompetent patients and of viruses and fungi in immunocompromised patients.

Etiology reference

  • 1. Kalil AC, Metersky ML, Klompas M, et al: Management of adults with hospital-acquired and ventilator-associated pneumonia: 2016 clinical practice guidelines by the Infectious Diseases Society of America and the American Thoracic Society. Clinical Infectious Diseases 63(5):e61–111, 2016.

Symptoms and Signs of Hospital-Acquired Pneumonia

Symptoms and signs of hospital-acquired pneumonia in nonintubated patients are generally the same as those for community-acquired pneumonia and include malaise, fever, chills, rigor, cough, dyspnea, and chest pain.

Diagnosis of Hospital-Acquired Pneumonia

  • Chest x-ray or chest computed tomography (CT) and clinical criteria (limited accuracy)
  • Sometimes bronchoscopy or blood cultures

Usually, a diagnosis is made based upon a new lung infiltrate combined with clinical features of infection, which include the new onset of fever, purulent sputum, leukocytosis, and decline in oxygenation. However, clinical diagnosis is imperfect. No symptom, sign, or x-ray finding is sensitive or specific for the diagnosis of hospital-acquired pneumonia, because all can be caused by atelectasis, pulmonary embolism, or pulmonary edema.

Gram stain and semiquantitative cultures of sputum samples, though not definitive for identifying infection, should be done because they can direct empiric therapy. Bronchoscopic sampling of lower airway secretions for quantitative culture yields more reliable specimens that can differentiate colonization from infection. Information gained from bronchoscopic sampling reduces antibiotic use and assists in switching from broader to narrower antibiotic coverage. However, it has not been shown to improve outcomes.

Measurement of inflammatory mediators in bronchoalveolar lavage fluid or serum has not been shown to be reliable in deciding on initiation of antibiotics. The only finding that reliably identifies both pneumonia and the responsible organism is a pleural fluid culture (obtained via thoracentesis in a patient with pleural effusion) that is positive for a respiratory pathogen.

Blood cultures are relatively specific if a respiratory pathogen is identified but are insensitive. Molecular tests that identify the pathogen and resistance patterns in respiratory secretions are emerging and could be useful in guiding treatment.

Prognosis for Hospital-Acquired Pneumonia

The mortality associated with hospital-acquired pneumonia is high despite the availability of effective antibiotics. However, not all mortality is attributable to the pneumonia itself; many of the deaths are related to the patient's other underlying illness. Adequacy of initial antimicrobial therapy clearly improves prognosis. Infection with antibiotic-resistant gram-negative or gram-positive bacteria worsens prognosis.

Treatment of Hospital-Acquired Pneumonia

  • Empirically chosen antibiotics active against resistant organisms

If hospital-acquired pneumonia is suspected, treatment is with antibiotics that are chosen empirically based on

  • Local sensitivity patterns
  • Patient risk factors for antibiotic-resistant pathogens

In the 2007 guidelines, the Infectious Diseases Society of America and the American Thoracic Society used very broad criteria for defining the population at risk of infection with antibiotic-resistant pathogens, which resulted in the majority of patients with HAP requiring broad-spectrum antibiotic therapy for MRSA and resistant Pseudomonas. The current, 2016 recommendations (1) emphasize use of a narrower spectrum of empiric antibiotics when possible. Empiric therapy for hospital-acquired pneumonia without increased risk for antibiotic-resistant bacteria due to prior IV antibiotic use within 90 days in an institution where MRSA incidence is < 20% (of S. aureus isolates) and P. aeruginosa resistance is < 10% for commonly used empiric antipseudomonal antibiotics, could include any one of the following:

Doses depend on renal function (see table Usual Doses of Commonly Prescribed Antibiotics).

In treatment settings where MRSA rates are > 20%, vancomycin or linezolid should be added. In patients who have risk factors for antibiotic-resistant organisms, or in the absence of reliable local antibiograms, recommendations include triple therapy using 2 drugs with activity against Pseudomonas and 1 drug with activity against MRSA:

  • An antipseudomonal cephalosporin (cefepime or ceftazidime) or an antipseudomonal carbapenem (imipenem, meropenem) or a beta-lactam/beta-lactamase inhibitor (piperacillin/tazobactam)
  • An antipseudomonal fluoroquinolone (ciprofloxacin or levofloxacin) or an aminoglycoside (amikacin, gentamicin, tobramycin)
  • Linezolid or vancomycin

While indiscriminate use of antibiotics is a major contributor to development of antimicrobial resistance, adequacy of initial empiric antibiotics is a major determinant of a favorable outcome. Therefore, treatment must begin with initial use of broad-spectrum drugs, which are then changed to the narrowest regimen possible based on clinical response and the results of cultures and antibiotic susceptibility testing.

Incentive spirometry is recommended to help prevent postoperative pneumonia.

Treatment reference

  • 1. Kalil AC, Metersky ML, Klompas M, et al: Management of adults with hospital-acquired and ventilator-associated pneumonia: 2016 clinical practice guidelines by the Infectious Diseases Society of America and the American Thoracic Society. Clinical Infectious Diseases 63(5):e61–111, 2016.

Key Points

  • Hospital-acquired pneumonia (HAP) is pneumonia that develops at least 48 hours after hospital admission in patients not receiving mechanical ventilation.
  • Likely pathogens differ from those causing community-acquired pneumonia and may require initial empiric antibiotic therapy that is active against antibiotic-resistant organisms.
  • Diagnosis is difficult, with culture of a potential pathogen from pleural fluid or blood being the most specific finding.
  • Reassess patients 2 to 3 days after initiation of treatment, and change antibiotics based on available culture and clinical data.

Drugs Mentioned In This Article

Drug Name Select Trade
Piperacillin/tazobactam ZOSYN
ciprofloxacin CILOXAN, CIPRO
ceftazidime FORTAZ, TAZICEF
tobramycin TOBI, TOBREX
gentamicin GENOPTIC
vancomycin VANCOCIN
Meropenem MERREM
linezolid ZYVOX
amikacin No US brand name

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