What infections can cause lymphopenia?

Infections That Cause Lymphopenia

Viral infections are the most common infectious cause of lymphopenia, with HIV being the most clinically significant, followed by other viral pathogens including cytomegalovirus (CMV), Epstein-Barr virus (EBV), and dengue. 1

Viral Infections

HIV and Opportunistic Infections

• HIV infection is the primary viral cause of persistent lymphopenia, particularly affecting CD4+ T-cells 2
• Patients with idiopathic CD4+ lymphopenia (ICD4L) present with opportunistic infections similar to HIV, including:
  • Cryptococcal infections (most frequent presentation) 2
  • Non-tuberculous mycobacterial infections 2
  • Persistent human papillomavirus (HPV) infection 2
  • Pneumocystis jirovecii pneumonia (PCP) 2
  • Mycobacterium avium complex 2

Other Viral Pathogens

• Cytomegalovirus (CMV) causes lymphopenia and can present with pneumonia, encephalitis, or gastrointestinal lesions 2
• Dengue virus commonly causes lymphopenia and thrombocytopenia 2
• Acute viral infections generally cause transient lymphopenia through abnormal lymphocyte trapping 3
• Herpes viruses (HSV, VZV) can cause lymphopenia, particularly in immunocompromised hosts 2
• ECHO viruses specifically cause CNS infections in patients with agammaglobulinemia and lymphopenia 2

Bacterial Infections

Mycobacterial Infections

• Mycobacterium tuberculosis causes severe transient lymphopenia that improves with anti-tuberculosis therapy 4
• Non-tuberculous mycobacteria (NTM) are associated with CD4+ lymphopenia 2

Other Bacterial Pathogens

• Typhoid fever (caused by Salmonella typhi) characteristically causes lymphopenia 2
• Septic shock from any bacterial source causes lymphopenia through abnormal lymphocyte trapping 3, 5
• Streptococcus pneumoniae and Haemophilus influenzae cause recurrent infections in patients with underlying lymphopenia from hematologic malignancies 2

Fungal Infections

• Cryptococcosis is the most frequent opportunistic fungal infection in patients with CD4+ lymphopenia 2
• Pneumocystis jirovecii causes pneumonia in patients with CD4+ counts <200/mm³ 2
• Aspergillosis can occur in severely lymphopenic patients 2

Parasitic Infections

• Toxoplasmosis causes brain lesions in patients with severe lymphopenia and low CD4+ counts 2
• Cryptosporidium causes gastrointestinal infections in lymphopenic patients 2

Clinical Context and Mechanisms

Mechanism of Infection-Related Lymphopenia

Viral infections induce lymphopenia through multiple mechanisms 1:

• Direct viral cytopathic effects on lymphocytes
• Abnormal lymphocyte trapping in lymphoid tissues 3, 5
• Increased lymphocyte apoptosis and catabolism 3

When to Suspect Opportunistic Infections

Suspect opportunistic infections when CD4+ T-cell counts are persistently <300 cells/mL in the absence of HIV 2

For patients with CD4+ counts <200/mm³, initiate prophylaxis for:

• Pneumocystis jirovecii 2
• Mycobacterium avium complex 2
• Consider CMV screening 2

Important Clinical Pitfall

Lymphadenopathy on imaging (including PET/CT) in lymphopenic patients may represent infection rather than malignancy, particularly with higher viral loads and lower CD4+ counts 2. Always perform infectious disease workup including cultures and biopsy before assuming malignant etiology 2.

Severe Presentations

Septic shock is strongly associated with lymphopenia (RR 2.72; 95% CI 1.02-7.21) and carries significantly increased mortality risk 6.