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PATIENT 
Ms. L is a 22-year-old woman who comes to your office in August complaining of cough and fever. She reports that she was in her usual state of health until 3 days ago when a cough developed. Two days ago, a low-grade fever (37.8°C) developed, which increased to 38.8°C yesterday. She reports that her sputum is yellow and that she has no chest pain or shortness of breath.
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CONSTRUCTING A DIFFERENTIAL DIAGNOSIS
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The causes of cough and congestion vary from trivial self-limited upper respiratory viral infections to serious, imminently life-threatening forms of pneumonia. The approach to such patients focuses on 2 pivotal questions. First, does the patient have symptoms, signs, or risk factors for pneumonia that warrant a chest radiograph or other evaluation? Second, in patients with pneumonia, is it simply a community-acquired pneumonia (CAP) or another type of pneumonia that requires alternative/additional treatment (such as Pneumocystis jirovecii pneumonia [PCP] or tuberculosis [TB])?
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A variety of symptoms suggest pneumonia because they are unusual in upper respiratory tract infections or bronchitis. These include dyspnea, high fever (with the exception of influenza [see below]), altered mental status, hypoxia, hypotension, dullness to percussion, crackles, decreased breath sounds, bronchophony, or egophony. Any patient with such symptoms or signs requires a minimum evaluation with a chest radiograph to rule out pneumonia. A chest radiograph should also be strongly considered in patients at increased risk for poor outcomes, including immunocompromised patients; elderly patients; and those with heart failure (HF), chronic kidney disease, or chronic obstructive pulmonary disease (COPD) (in whom abnormal lung findings are also more difficult to appreciate). Figure 10-1 shows a diagnostic algorithm illustrating the initial approach to patients with cough and congestion.
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In patients with pneumonia, the next pivotal step is to determine the likely etiologic pathogen(s), which will ensure patients receive appropriate therapy. Even in ...