Can pneumonia cause eosinophilia (elevated eosinophil count)?

From the Guidelines

Pneumonia can cause eosinophilia, particularly in cases of parasitic or fungal infections, as evidenced by the presence of eosinophilia in up to 70% of patients with Strongyloides stercoralis infection 1.

Causes of Eosinophilia in Pneumonia

• Parasitic infections such as Strongyloides stercoralis, which can cause pneumonia and lead to eosinophilia 1
• Fungal infections like Aspergillus or Coccidioides, which can trigger an immune response and increase eosinophil counts
• Atypical bacterial pneumonias, including Mycoplasma or Chlamydia, which can also cause eosinophilia

Importance of Diagnosis

It is crucial to determine the underlying cause of eosinophilia in patients with pneumonia, as treatment approaches may differ from standard pneumonia protocols.

• Accurate diagnosis is essential to establish the appropriate treatment plan, taking into account histopathologic, clinical, laboratory, cytogenetic, and molecular criteria 1
• Ruling out secondary (reactive) eosinophilia caused by nonneoplastic or neoplastic conditions is necessary to provide targeted treatment

Clinical Considerations

• Common bacterial pneumonias typically cause neutrophilia rather than eosinophilia
• Other non-infectious causes of eosinophilic pneumonia, such as medication reactions, autoimmune conditions, and allergic bronchopulmonary aspergillosis, should be considered in the differential diagnosis
• Monitoring of serum IgG4 concentration might have some value for the assessment of disease activity in certain cases, although its use is still limited and controversial 1

From the Research

Eosinophilia and Pneumonia

• Eosinophilia can be associated with certain types of pneumonia, particularly those caused by parasitic infections or other non-infectious causes 2, 3, 4.
• The eosinophilic pneumonias are a heterogeneous group of diseases characterized by an increase in eosinophils in lung tissue or bronchoalveolar lavage fluid, and many are also associated with peripheral blood eosinophilia 3.
• Some studies suggest that pneumonia caused by parasitic infections, such as paragonimiasis, can induce eosinophilia in humans 5, 6.

Causes of Eosinophilic Pneumonia

• Parasitic infections, such as those caused by Ascaris, hookworms, Strongyloides, Paragonimus, filariasis, and Toxocara, can cause eosinophilic pneumonia 4.
• Non-infectious causes, including allergic sensitization to Aspergillus, acute and chronic eosinophilic pneumonias, Churg-Strauss syndrome, hypereosinophilic syndromes, and pulmonary eosinophilia due to exposure to specific medications or toxins, can also lead to eosinophilic pneumonia 4.
• Paragonimiasis, a parasitic foodborne infection, can induce systemic symptoms with eosinophilia in humans and can be distinguished from chronic eosinophilic pneumonia by the presence of pneumothorax and other symptoms 6.

Diagnosis and Treatment

• The diagnosis of eosinophilic pneumonia is made when both characteristic clinical-imaging features and alveolar eosinophilia are present, and peripheral blood eosinophils are generally markedly elevated 2.
• Corticosteroids are the cornerstone of therapy for many eosinophilic pneumonias, particularly for both acute and chronic eosinophilic pneumonias, and prognosis is typically excellent provided treatment is initiated in a timely manner 2, 3.
• In cases of paragonimiasis, the drug of choice is praziquantel, and triclabendazole can be used in certain cases 5.