What is the diagnostic approach for patients suspected of having Cytomegalovirus (CMV) or Epstein-Barr Virus (EBV) infections, particularly in immunocompromised patients?

Diagnostic Approach for CMV and EBV Infections

For immunocompromised patients, CSF PCR for CMV has 82-100% sensitivity and 86-100% specificity, making it the gold standard for CNS disease, while quantitative CMV DNA PCR in blood is preferred over serology for systemic disease monitoring. 1 For EBV, begin with heterophile antibody testing in immunocompetent patients, but proceed directly to EBV-specific antibody panel (VCA IgM, VCA IgG, EBNA) if negative, and use quantitative EBV viral load testing by nucleic acid amplification in immunocompromised patients rather than serology. 2, 3

CMV Diagnostic Algorithm

Immunocompromised Patients (Transplant Recipients, HIV, Immunosuppressive Therapy)

• Order quantitative CMV DNA PCR (viral load) as first-line test, NOT serology 4, 5
• CMV viral load monitoring by nucleic acid amplification test (NAAT) is the recommended approach in transplant recipients 4
• For suspected CMV end-organ disease, order CMV DNA PCR from the affected site: cerebrospinal fluid for CNS disease, respiratory specimens for pneumonitis, colon biopsy tissue for colitis 4
• CSF PCR for CMV achieves sensitivity of 82-100% and specificity of 86-100% in immunocompromised persons 1
• CMV pp65 antigenemia testing is useful for screening transplant recipients, as it is more rapid and sensitive than culture 4
• Weekly screening from day 10 to day 100 post-transplant using either pp65 antigenemia or PCR enables preemptive treatment 4

Immunocompetent Patients

• Order CMV IgM and IgG antibodies as first-line test 4
• CMV IgM positive indicates recent/acute infection 4
• CMV IgG positive alone indicates past exposure only, NOT active infection 4
• Over 90% of normal adults have IgG antibodies to CMV from past exposure 4

Tissue-Based CMV Disease

• Immunohistochemistry (IHC) on tissue biopsy is the gold standard for diagnosing CMV in tissue-based disease 4
• IHC detects CMV immediate early antigens with 78-93% sensitivity and 92-100% specificity 4
• CMV immunohistochemistry or in situ hybridization should be performed on formalin-fixed, paraffin-embedded tissue for any tissue biopsy 4

Critical Pitfall for CMV

• Never rely on serology alone in immunocompromised patients—viral load testing or tissue diagnosis is essential 4
• False-positive CMV IgM results can occur in patients with EBV infection or other conditions causing immune system activation 4
• Do not assume positive tissue PCR alone confirms CMV disease; correlation with histology/IHC and blood PCR/antigenemia is necessary to distinguish true disease from colonization 4

EBV Diagnostic Algorithm

Immunocompetent Patients with Suspected Infectious Mononucleosis

• Start with complete blood count with differential and rapid heterophile antibody test (Monospot) 3
• A positive Monospot test is diagnostic for EBV infection and no further EBV-specific testing is required 2
• If Monospot is negative but clinical suspicion remains high, proceed directly to EBV-specific antibody testing: VCA IgM, VCA IgG, and EBNA antibodies 2, 3
• Do not wait to repeat Monospot—order EBV-specific antibodies on the same sample 2

Interpreting EBV Antibody Results

• Primary acute EBV infection: VCA IgM positive AND EBNA antibodies absent 2, 3
• Past infection: EBNA antibodies present (develops 1-2 months after primary infection and persists for life) 2, 3
• VCA IgG develops rapidly in acute infection 3
• Over 90% of normal adults have IgG antibodies to VCA and EBNA from past infection 3
• Presence of EBNA antibodies makes EBV unlikely as cause of current acute symptoms 2

Immunocompromised Patients (Transplant Recipients, HIV, Congenital Immunodeficiencies)

• Order quantitative EBV viral load testing by nucleic acid amplification (NAAT) in peripheral blood, NOT serology 2, 3
• These patients are at high risk for EBV-associated lymphoproliferative disease 2, 3
• EBV DNA levels >10^2.5 copies/mg DNA in peripheral blood mononuclear cells indicate active infection 2

Special Population Considerations

• Children under 10 years: heterophile antibody tests have higher false-negative rates (approximately 10%)—proceed directly to EBV-specific antibody testing 1, 3
• Heterophile antibody typically becomes detectable between days 6-10 after symptom onset and peaks during weeks 2-3 of illness 3
• False-positive heterophile results can occur with leukemia, pancreatic carcinoma, viral hepatitis, and CMV infection 3

CNS Involvement

• For suspected EBV-associated encephalitis, perform both CSF PCR and serology (VCA IgM/IgG and EBNA) 1, 2
• CSF PCR for EBV results may be false positive, so interpret in conjunction with serologic testing 1
• Quantitative PCR should be done because a low CSF copy number may be an incidental finding 1

Critical Pitfalls for EBV

• Do not order EBV testing from throat swabs—EBV can persist in throat secretions for weeks to months after infection and does not confirm acute infection 2, 3
• Do not rely solely on heterophile testing in children under 10 years 3
• Consider alternative diagnoses including CMV, adenovirus, HIV, and Toxoplasma gondii when evaluating mononucleosis-like illness 3
• Approximately 5-10% of EBV-infected patients fail to develop EBNA antibodies 3

CMV and EBV Co-Testing Considerations

When to Test Both Simultaneously

• In fever of unknown origin with negative Monospot, test both EBV-specific antibodies and CMV antibodies, as CMV represents a common cause of mononucleosis-like syndromes 3
• False-positive CMV IgM results can occur in patients infected with EBV, highlighting the importance of testing both simultaneously to avoid diagnostic confusion 3
• Mononucleosis-like syndromes (including both EBV and CMV) account for 0.8% of fever cases in returning travelers 3

Encephalitis Workup

• All patients with suspected encephalitis should have CSF PCR for HSV-1, HSV-2, VZV, and enteroviruses as first-line, with EBV and CMV considered based on immune status 1
• For immunocompromised patients with encephalitis, CSF PCR for both EBV and CMV should be performed 1

Summary of Key Testing Differences

Clinical Scenario	CMV Testing	EBV Testing
Immunocompetent patient	IgM and IgG serology [4]	Heterophile test, then VCA IgM/IgG and EBNA if negative [2,3]
Immunocompromised patient	Quantitative DNA PCR (viral load) [4,5]	Quantitative DNA PCR (viral load) [2,3]
CNS disease	CSF PCR (sensitivity 82-100%) [1]	CSF PCR + serology [1,2]
Tissue disease	IHC on biopsy (gold standard) [4]	Not applicable—EBV rarely requires tissue diagnosis
Transplant monitoring	Weekly pp65 antigenemia or PCR [4]	Quantitative viral load [2,3]