What infections can cause eosinopenia?

Common Infections Causing Eosinopenia

Bacterial and viral infections are the most common causes of eosinopenia, with sepsis being a particularly reliable marker of acute infection. 1, 2

Mechanism of Eosinopenia in Infections

Eosinopenia (abnormally low eosinophil count) occurs during acute infections as part of the body's physiological response to infection. This is in contrast to eosinophilia (elevated eosinophil count), which is commonly associated with parasitic infections, allergic reactions, and certain other conditions.

Bacterial Infections Causing Eosinopenia

• Sepsis: Eosinopenia is a highly reliable marker of sepsis, with studies showing it has good diagnostic value in distinguishing between non-infection and infection 2

  • Sensitivity of 80% and specificity of 91% at a cutoff of <50 cells/mm³
  • Particularly useful in ICU settings as an early marker of infection

• Severe bacterial pneumonia: Associated with marked reduction in circulating eosinophils 3

• Gram-negative bacteremia: Particularly in the context of Strongyloides hyperinfection syndrome 4

Viral Infections Causing Eosinopenia

• COVID-19: Severe eosinopenia (absolute eosinophil count = 0 G/L) is associated with poor outcomes in COVID-19 patients 5, 6

  • Present in approximately 51% of hospitalized COVID-19 patients
  • Associated with higher need for intensive respiratory support and higher mortality
  • Reflects hyperactive immune response during severe infection

• Acute viral respiratory infections: Common cause of transient eosinopenia 3

Clinical Significance and Monitoring

1. Diagnostic value: Eosinopenia can serve as a simple, inexpensive biomarker for acute infection, particularly bacterial infections 1

2. Prognostic indicator: In COVID-19 and sepsis, eosinopenia correlates with disease severity and poor outcomes 5, 6

3. Monitoring recovery: The normalization of eosinophil counts can indicate the remission phase of infection 3

   • Mean eosinophil count: 46 cells/mm³ during acute infection vs. 252 cells/mm³ during remission

Distinguishing Features from Parasitic Infections

While bacterial and viral infections typically cause eosinopenia, parasitic infections generally cause eosinophilia. However, there are important exceptions:

• Acute schistosomiasis (Katayama syndrome): Despite being a parasitic infection, eosinophilia can occasionally be absent 4

• Strongyloides hyperinfection: Severe cases may not have eosinophilia despite being a parasitic infection 4

Management Implications

1. Early recognition: Eosinopenia should prompt consideration of bacterial or viral infection, particularly in critically ill patients

2. Monitoring treatment response: Rising eosinophil counts may indicate effective treatment and transition to recovery phase 3

3. Differential diagnosis: In returning travelers with fever, eosinopenia suggests bacterial/viral infection rather than parasitic infection, which typically causes eosinophilia 4

Pitfalls and Caveats

1. Not specific to particular pathogens: Eosinopenia is a general marker of acute infection rather than indicating a specific pathogen

2. Confounding factors: Corticosteroid use can cause eosinopenia independent of infection 3

3. Interpretation in context: Eosinopenia should be interpreted alongside other clinical and laboratory findings, not in isolation

4. Normalization during recovery: Expect eosinophil counts to normalize during the recovery phase of infection 3

In summary, while eosinophilia is commonly associated with parasitic infections, eosinopenia is a valuable marker of acute bacterial and viral infections, particularly sepsis and severe COVID-19, and can help guide diagnostic and treatment decisions in acutely ill patients.