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Hospital-acquired pneumonia

Updated May 21, 2025

Background

Overview

Definition

HAP (nosocomial pneumonia) is a lower respiratory infection occurring in patients at least 48 hours after admission to the hospital, or within 14 days after discharge from the hospital.

Pathophysiology

The three main infection routes include inhalation (most common), aspiration and hematogenous dissemination (rare). HAP is most frequently caused by S. aureus (especially, MRSA), Pseudomonas species (especially P. aeruginosa), Acinetobacter species, E. coli, and Klebsiella species (including extended-spectrum β-lactamase-producing and extensively drug-resistant Enterobacteriaceae). Other pathogens include S. maltophilia, Chryseobacterium species, E. meningoseptica.

Epidemiology

The incidence of HAP (HAP) in the US is estimated at 363 per 100,000 patient-days.

Disease course

Clinical manifestations of HAP are similar to community-acquired pneumonia. Typical pneumonia is characterized by severe malaise, fever, chills, productive cough with purulent sputum (yellow-greenish), dyspnea, and pleuritic chest pain associated with rales and increased tactile fremitus. Atypical HAP presents with extrapulmonary manifestations (eg. myalgia, nervous system impairment, and gastrointestinal symptoms).

Prognosis and risk of recurrence

Prognosis of HAP is highly dependent on risk factors and comorbidities. However, multidrug-resistant HAP is associated with higher mortality.

Guidelines

Key sources

The following summarized guidelines for the management of hospital-acquired pneumonia are prepared by our editorial team based on guidelines from the British Thoracic Society (BTS 2023), the European Society of Intensive Care Medicine (ESICM/ALAT/ERS/ESCMID 2017), the Infectious Diseases Society of America (IDSA/ATS 2016), and the Infectious Diseases Society of America (IDSA 2011,2007).

Medical management

Initiation of treatment: as per ATS/IDSA 2016 guidelines, use clinical criteria alone to decide whether or not to initiate antibiotic therapy in patients with suspected HAP.

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Inpatient care

Clinical monitoring: as per ALAT/ERS/ESCMID/ESICM 2017 guidelines, obtain routine bedside clinical assessment with the following in patients with HAP receiving antibiotic therapy

temperature monitoring

measurement of tracheobronchial secretion volume

culture and purulence assessment of tracheobronchial secretions

evaluation for CXR resolution

WBC count

paO2/FiO2

assessment of ≥ 1 clinical scores, such as CPIS, ODIN, SOFA, SAPS II, and APACHE II.

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APACHE II

Calculator

When to use

Age (years)

< 45

45-54

55-64

65-74

≥ 75

Rectal temperature (°C [°F])

< 30 [< 86]

30-31.9 [86-89.5]

32-33.9 [89.6-93.1]

34-35.9 [93.2-96.7]

36-38.4 [96.8-101.2]

38.5-38.9 [101.3-102.1]

39-40.9 [102.2-105.7]

≥ 41 [≥ 105.8]

Mean arterial pressure (mmHg)

≥ 160

130-159

110-129

70-109

50-69

< 50

Arterial pH

≥ 7.7

7.6-7.69

7.5-7.59

7.33-7.49

7.25-7.32

7.15-7.24

< 7.15

Heart rate (bpm)

≥ 180

140-179

110-139

70-109

55-69

40-54

< 40

Respiratory rate (rpm)

≥ 50

35-49

25-34

12-24

10-11

6-9

< 6

Serum sodium (mEq/L)

≥ 180

160-179

155-159

150-154

130-149

120-129

111-119

< 111

Serum potassium (mEq/L)

≥ 7.0

6.0-6.9

5.5-5.9

3.5-5.4

3.0-3.4

2.5-2.9

< 2.5

Serum creatinine (mg/dL)

≥ 3.5

2.0-3.4

1.5-1.9

0.6-1.4

< 0.6

Acute renal failure

Yes

Hematocrit (%)

≥ 60

50-59.9

46-49.9

30-45.9

20-29.9

< 20

White blood cell count (×10**3/mcL)

≥ 40

20-39.9

15-19.9

3-14.9

1-2.9

< 1

Glasgow Coma Scale (GCS)

Oxygenation (use PaO₂ if FiO₂ < 50% or non-intubated, otherwise use A-a gradient; mmHg)

PaO₂ > 70

PaO₂ 61-70

PaO₂ 55-60

PaO₂ < 55

A-a < 200

A-a 200-349

A-a 350-499

A-a ≥ 500

Setting

Nonoperative

Emergency surgery

Elective surgery

Severe organ failure (liver cirrhosis, congestive heart failure, chronic lung disease, chronic kidney disease on dialysis) or immunocompromise

Yes

Calculation

Please enter all the required inputs.

The Acute Physiology and Chronic Health Evaluation II (APACHE II) is a severity-of-disease classification system, specifically designed for critically ill patients admitted to the intensive care unit (ICU). It is a composite score that incorporates 12 physiological variables (including vital signs, arterial blood gas measurements, and serum biochemical parameters), age, and chronic health status. The score ranges from 0 to 71, with higher scores indicating a higher severity of illness and a higher risk of mortality. The APACHE II score is primarily used to predict ICU mortality, and it can also provide an estimate of ICU length of stay. It is a valuable tool for risk stratification, enabling clinicians to identify patients who may require more intensive monitoring and intervention, and facilitating communication about patient prognosis. However, the APACHE II score should not be used in isolation to guide clinical decision-making, as it does not account for all individual patient factors. It is also not applicable to pediatric patients or to patients admitted to the ICU after cardiac surgery, as it was not validated in these populations.

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Specific circumstances

Patients with aspiration pneumonia, diagnosis: as per BTS 2023 guidelines, recognize that aspiration pneumonia is particularly common in persons with a learning disability, in older persons, and in patients with neurological or upper gastrointestinal conditions.

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Quality improvement

Local susceptibility assessments: as per ATS/IDSA 2016 guidelines, ensure regular generation and dissemination of local antibiograms in all hospitals, ideally tailored to their HAP population, if possible.

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