Differential Diagnosis for Bacterial vs Fungal Pneumonia

Single Most Likely Diagnosis

• Bacterial Pneumonia: This is the most common cause of pneumonia, with Streptococcus pneumoniae being the most frequently identified pathogen. The presentation typically includes symptoms such as cough, fever, and shortness of breath, which aligns with the classic symptoms of pneumonia.

Other Likely Diagnoses

• Viral Pneumonia: Viruses are a common cause of pneumonia, especially in certain populations like the elderly, young children, and those with compromised immune systems. Influenza, respiratory syncytial virus (RSV), and adenovirus are common viral pathogens.
• Fungal Pneumonia: This is more likely in immunocompromised patients, such as those with HIV/AIDS, undergoing chemotherapy, or taking immunosuppressive drugs. Pneumocystis jirovecii pneumonia (PCP) is a classic example in this population.
• Mycoplasma Pneumonia: Caused by Mycoplasma pneumoniae, this type of pneumonia is often seen in younger adults and can present with symptoms similar to those of bacterial pneumonia but tends to be milder.

Do Not Miss Diagnoses

• Tuberculous (TB) Pneumonia: Although less common in some regions, TB can present with symptoms similar to those of bacterial pneumonia. Missing this diagnosis can have significant consequences due to the need for specific treatment and public health implications.
• Pneumocystis jirovecii Pneumonia (PCP): In immunocompromised patients, PCP can be life-threatening and requires prompt treatment. It often presents with non-specific symptoms such as dry cough and progressive shortness of breath.
• Influenza Pneumonia: Especially during influenza season, this can be a critical diagnosis to make due to the availability of antiviral treatments and the potential for severe disease in certain populations.

Rare Diagnoses

• Actinomycotic Pneumonia: Caused by Actinomyces species, this is a rare form of pneumonia that can mimic other forms of pneumonia or even lung cancer in its presentation.
• Nocardial Pneumonia: Caused by Nocardia species, this is more common in immunocompromised patients and can present with a variety of pulmonary and extrapulmonary symptoms.
• Parasitic Pneumonia: Such as that caused by Paragonimus westermani (lung fluke), which is rare and typically associated with specific geographic or exposure histories.