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CHAPTER 65: Pneumonia 585

Epidemics of Legionnaire disease have been described in nursing TABLE 65-7 Differential Diagnosis of Hospital-Acquired Pneumonia
home patients. Unfortunately, patients from one nursing home may
end up in several hospitals, making recognition of this common source Atelectasis
infection more difficult. Epidemics of viral pneumonia have also been Aspiration pneumonitis
reported in nursing home patients. Atypical pulmonary edema a

Pleural effusion a
HOSPITAL-ACQUIRED PNEUMONIA
Drug-induced lung disease
In many institutions and in many critical care units, particularly non- Hypersensitivity pneumonitis
medical ICUs, HAP is clearly a more common reason for ICU admission
than CAP. While this is not surprising, the fact that HAP is now more Acute eosinophilic pneumonia
common in the ICU than VAP is not generally appreciated. A recent Vasculitis
study from four academic medical centers in the United States found Pulmonary embolus/infarction
that only 32% of pneumonias in these ICUs were VAP. Of the cases
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of HAP, >75% were mechanically ventilated, with most developing Malignancy
respiratory failure as a result of pneumonia. Approximately 25% of cases Pulmonary hemorrhage
developed pneumonia within 48 hours of intubation. While technically a Fever and/or leukocytosis secondary to extrapulmonary infection.
HAP, some of these patients may instead have early-onset VAP associ-
ated with an aspiration episode in the periintubation time period rather
than delayed clinical manifestations of HAP. This study parallels the majority of etiologic diagnoses for HAP are therefore made from blood
experience in many intensive care units and illustrates the significant cultures. However, as many as 30% of positive blood cultures in hospi-
problem that HAP is for critical care physicians. talized patients with pulmonary infiltrates are due to other infections,
particularly central-line infections. This dependence on positive blood
■ ALTERED PATHOGENESIS AND PATHOPHYSIOLOGY cultures skews the apparent etiologic spectrum toward pathogens more
HAP, like HCAP, represents an intermediate syndrome between CAP likely to be invasive, including MRSA and Pseudomonas.
and VAP. Patients who develop HAP are often colonized with MDR Invasive Diagnosis: One randomized trial of invasive diagnosis of non-
pathogens, similar to patients with VAP. In contrast, development of ICU HAP in nonimmunocompromised patients found that an
pneumonia without exposure to high oxygen tension experienced by immediate bronchoscopy with protected specimen brush culture was
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patients on mechanical ventilation increases the probability that anaer- positive in 94%. Although no antibiotics and narrower spectrum
obes play a role in HAP. In general, patients with HAP have better host treatment were more common with invasive diagnosis, outcome
immune responses than do patients with VAP. Therefore, aggressive was not improved. In contrast, Kett et al found at least one potential
antibiotic therapy may be less critical and generally survival is greater pathogen in 75% of patients with ICU pneumonia when 87% of their
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than for VAP. Interestingly, because patients who develop HAP do not patients were intubated. While the one-third of patients with VAP
have as many restrictions on hospital visitors, hospital acquisition of probably increased this percentage, access to the lower respiratory
respiratory viral pneumonia is much more common in HAP than VAP. tract via the endotracheal tube is likely the most important reason for
The underlying diseases precipitating hospital admission, for example, the higher diagnostic yield.
stroke or acute hepatic failure, increase the risk of aspiration compared An RCT of early bronchoscopy (compared to noninvasive testing
to typical CAP. However, many of these patients have intact host immu- followed by bronchoscopy at day 3 if clinical failure) in hematology/
nity and, therefore, the ability to avoid development of pneumonia oncology patients admitted to the ICU with pulmonary infiltrates found
oftentimes rests on the primary cause for hospital admission. Patients no difference in the percent of patients without a diagnosis, associated
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with HAP may have some blunting of their inflammatory response mortality, or need for subsequent intubation. Early bronchoscopy
because of typical causes for hospital admission. For this reason they alone established the diagnosis in <20%, with the majority still made by
may not manifest signs and symptoms of pneumonia as dramatically noninvasive tests. A slightly greater frequency of viral pneumonia was
as patients with CAP. Once again, the primary determinant of bacterial demonstrated in patients with delayed bronchoscopy, suggesting that
etiology is prior antibiotic therapy. failure to respond to empirical antibiotics may indicate viral infection.
■ DIAGNOSIS ted to the ICU is that early invasive diagnostic testing in nonintubated
Synthesis of the limited data on diagnosis of HAP in patients admit-

The clinical diagnosis of HAP is more difficult than for CAP and the patients is probably not warranted. In contrast, once intubated, aggres-
sive sampling of the lower respiratory tract with tracheal aspirates, non-
diagnostic armamentarium is much more limited than for VAP, since
access to the lower respiratory tract via an endotracheal tube is not bronchoscopic BAL, or bronchoscopy is probably warranted.
present to the ICU with HAP, the high frequency of recent changes in ■ ETIOLOGIC SPECTRUM
routinely available. Despite intubation of a large fraction of patients who
antibiotic therapy compromise subsequent cultures. No conclusive study is available for etiology specifically of HAP patients
The differential diagnosis of pneumonia in patients with HAP is admitted to the ICU. Therefore, the spectrum of etiologies must be
seen in Table 65-7. Atelectasis is a much larger concern for HAP, given inferred from the few available studies. Early bronchoscopy of non-
underlying diseases that often place patients at bed rest. Aspiration ICU HAP patients demonstrated a higher percentage of typical CAP
pneumonitis is also a major concern. Exacerbations of underlying pathogens, including pneumococcus, MSSA, and Legionella, with strep-
disease, including vasculitis and heart failure, are often difficult to dis- tococci causing up to a quarter of cases. Use of urinary antigen testing
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tinguish from HAP. Drug-induced lung disease is a particular issue with in these patients also confirmed that S pneumoniae and Legionella are
patients receiving chemotherapeutic agents. Hypersensitivity pneumo- important considerations. The former is likely only in patients who
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nitis and acute eosinophilic pneumonia have been described with many have not received prior antibiotics for any reason. The study of Kett
commonly prescribed drugs in hospitalized patients. et al (Fig. 65-3) specifically focused on HAP admitted to the ICU but
Standard diagnostic tests have somewhat limited utility in non- inclusion of patients with VAP compromise the summary statistics.
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intubated patients with HAP. Expectorated sputum is often difficult However, only 10% of patients with ICU pneumonia did not have risk
to obtain and suspect for simple colonization. Urinary antigen tests factors for MDR pathogens and 20% were culture negative. Typical
for pneumococcus and Legionella are occasionally positive. 108,109 The CAP pathogens, other than MSSA, are most likely to be in these two

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