 Introduction/Background Acute respiratory illness (ARI) is defined as one or more of the following symptoms: cough, sputum production, chest pain, or dyspnea (with or without fever), usually in the setting of suspected respiratory infection. ARI is a major public health issue, being one of the most common reasons for doctor office or emergency department (ED) visits. Cough, chest pain, and dyspnea account for 3 of the top 10 presenting symptoms during ED visits [1]. Most cases of ARI are attributable to infection, and the major diagnostic dilemma for patients with ARI is distinguishing patients with self-limited viral infection from those with a bacterial pneumonia (PNA), such as community-acquired PNA. In 2014, PNA (combined with influenza) accounted for the eighth most common cause of death in the United States [2]. The primary role of imaging in patients with ARI is to aid in the diagnosis or exclusion of PNA. By helping to identify the subset of ARI patients with PNA, imaging helps separate patients who would benefit from antibiotic therapy from those who would not. This increases the chance that patients with PNA receive appropriate therapy and reduces the risks associated with inappropriate use of antibiotics in patients with viral causes of ARI. The need for imaging in the ARI patient may depend on a number of factors, which can include severity of illness; presence of fever, leukocytosis, or hypoxemia; clinical history; physical examination findings; patient age; and the presence of other risk factors. Not all studies concur as to which patients with ARI should have an initial imaging study. While chest radiographs have a long track record, they do have lower sensitivity for PNA relative to other imaging modalities such as CT. Self et al [5] performed an observational cross-sectional multicenter study that enrolled 3,423 ED patients presenting with ARI. This is one of the largest studies comparing chest radiographs and CT in the ED setting.
Acute Respiratory Illness in Immunocompetent Patients.  Introduction/Background Acute respiratory illness (ARI) is defined as one or more of the following symptoms: cough, sputum production, chest pain, or dyspnea (with or without fever), usually in the setting of suspected respiratory infection. ARI is a major public health issue, being one of the most common reasons for doctor office or emergency department (ED) visits. Cough, chest pain, and dyspnea account for 3 of the top 10 presenting symptoms during ED visits [1]. Most cases of ARI are attributable to infection, and the major diagnostic dilemma for patients with ARI is distinguishing patients with self-limited viral infection from those with a bacterial pneumonia (PNA), such as community-acquired PNA. In 2014, PNA (combined with influenza) accounted for the eighth most common cause of death in the United States [2]. The primary role of imaging in patients with ARI is to aid in the diagnosis or exclusion of PNA. By helping to identify the subset of ARI patients with PNA, imaging helps separate patients who would benefit from antibiotic therapy from those who would not. This increases the chance that patients with PNA receive appropriate therapy and reduces the risks associated with inappropriate use of antibiotics in patients with viral causes of ARI. The need for imaging in the ARI patient may depend on a number of factors, which can include severity of illness; presence of fever, leukocytosis, or hypoxemia; clinical history; physical examination findings; patient age; and the presence of other risk factors. Not all studies concur as to which patients with ARI should have an initial imaging study. While chest radiographs have a long track record, they do have lower sensitivity for PNA relative to other imaging modalities such as CT. Self et al [5] performed an observational cross-sectional multicenter study that enrolled 3,423 ED patients presenting with ARI. This is one of the largest studies comparing chest radiographs and CT in the ED setting.