Differential Diagnosis for Lower Respiratory Infection
Single Most Likely Diagnosis
- Pneumonia (community-acquired or hospital-acquired): This is the most common cause of lower respiratory infection, often presenting with symptoms such as cough, fever, and shortness of breath. The likelihood of pneumonia is high due to its prevalence and the broad range of pathogens that can cause it, including bacteria, viruses, and fungi.
Other Likely Diagnoses
- Acute bronchitis: Typically caused by viral infections, acute bronchitis presents with cough and sometimes mild fever, but without the systemic symptoms or radiographic findings of pneumonia.
- Influenza: A viral infection that can cause lower respiratory symptoms, especially during seasonal outbreaks. It often includes additional symptoms like myalgias and headache.
- Chronic obstructive pulmonary disease (COPD) exacerbation: For patients with a history of COPD, an exacerbation can present as a lower respiratory infection, with worsening of symptoms such as dyspnea, cough, and sputum production.
Do Not Miss Diagnoses
- Pulmonary embolism: Although it may not present with typical infectious symptoms, pulmonary embolism can cause sudden onset of dyspnea and chest pain, and is critical to diagnose due to its high mortality rate if untreated.
- Tuberculosis (TB): Especially in high-risk populations or areas with high TB prevalence, TB can present with chronic cough, weight loss, and night sweats, and is crucial to diagnose due to its public health implications and the need for specific treatment.
- Pneumocystis jirovecii pneumonia (PCP): In immunocompromised patients, PCP can cause severe pneumonia that is difficult to treat if not recognized early.
Rare Diagnoses
- Cystic fibrosis exacerbation: In patients with cystic fibrosis, an exacerbation can mimic a lower respiratory infection, with increased respiratory symptoms and decline in lung function.
- Bronchiectasis: A condition characterized by permanent dilation of parts of the airways, which can lead to recurrent lower respiratory infections.
- Fungal infections (e.g., aspergillosis, histoplasmosis): These can cause lower respiratory symptoms, especially in immunocompromised individuals, and require specific diagnostic tests and treatments.