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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 (37.2°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.

The framework for the differential diagnosis of acute respiratory complaints is anatomic and microbiologic. Although there are a myriad of viral and bacterial (and occasional mycobacterial) infections that infect the respiratory tree, a practical approach addresses 3 issues:

  1. Where is the infection (sinuses, tracheobronchial tree, alveoli)?

  2. Will the patient benefit from antibiotics?

  3. Among patients with pneumonia, clinicians must separate the common community-acquired pneumonias (CAPs) from the less common but important pneumonias due to aspiration, tuberculosis (TB), and opportunistic infections. Diagnostic and treatment algorithms that summarize the approach to patients with acute respiratory infections appear at the end of the chapter. (see Figures 9–3 and 9–4)

Figure 9-3.

Diagnostic approach: acute cough and fever.

Figure 9-4.

Response to the results of the CXR in patients with cough and fever.

Differential Diagnosis of Acute Coughand Congestion

  1. Common cold

  2. Sinusitis

  3. Bronchitis

  4. Influenza

  5. Pneumonia

    1. CAP

    1. Aspiration pneumonia

    1. TB

    1. Opportunistic (eg, Pneumocystis jiroveci pneumonia [PCP])

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On physical exam, Ms. L is in no acute distress. Vital signs are RR, 18 breaths per minute; BP, 110/72 mm Hg; pulse, 92 bpm; temperature, 38.6°C. Pharynx is unremarkable; lung exam reveals normal breath sounds without crackles, dullness, bronchophony, or egophony.

At this point, what is the leading hypothesis, what are the active alternatives, and is there a must not miss diagnosis? Given this differential diagnosis, what tests should be ordered?

The differential diagnosis for Ms. L includes acute bronchitis, influenza, aspiration pneumonia, and CAP. Ms. L's high fever is a pivotal feature of this case. Acute bronchitis is not usually associated with significant fever (unless caused by influenza). Influenza can cause high fevers and chest symptoms but almost always occurs between December and May. Therefore, despite Ms. L's normal lung exam, the high fever raises the possibility of CAP and makes this the leading diagnosis. Table 9–1 lists the differential diagnosis.

Table 9–1. Diagnostic Hypotheses for MS. L.

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