Should I get tested for mono (mononucleosis) if my boyfriend has it?

Testing for Mononucleosis in Asymptomatic Contacts

Testing asymptomatic contacts of patients with infectious mononucleosis is not recommended and provides no clinical utility for guiding exposure decisions. 1

Why Testing is Not Indicated

Epidemiology and Transmission Context

• Over 90% of adults already have antibodies to Epstein-Barr virus (EBV), indicating past infection, making most young adults already immune 1
• EBV is transmitted through intimate oral contact (saliva), and by the time a partner develops symptomatic mononucleosis, exposure has already occurred 2, 3
• The incubation period for infectious mononucleosis is 4-6 weeks, meaning if transmission occurred, the contact period happened well before symptom onset in the boyfriend 4, 3

Test Interpretation Problems

• A positive IgG result only indicates past infection (which 90% of adults have) and does not distinguish between recent exposure versus infection years ago 5, 6
• A negative test today does not mean she won't develop infection since she may be in the incubation period, with antibodies not yet detectable 1
• Heterophile antibodies (Monospot test) become detectable only 6-10 days after symptom onset, not during the incubation period, making them useless for detecting early or asymptomatic infection 1, 4
• False-negative heterophile tests occur in approximately 10% of patients, particularly early in illness 1

Clinical Decision-Making Cannot Be Based on Test Results

• If she tests positive for past EBV infection (IgG positive): This doesn't mean she's currently infected or immune to reinfection in a clinically meaningful way for this exposure 5, 6
• If she tests negative: She could still be in the incubation period and develop symptoms in the coming weeks, making the "stay away" strategy ineffective 7, 2
• The reasoning of "positive means spend time together, negative means stay away" is fundamentally flawed because the test cannot predict current infection status or future disease development 1

Recommended Approach

What to Actually Do

• Counsel that exposure has likely already occurred if they've had intimate contact (kissing, sharing drinks/utensils) in the past 6 weeks 2, 3
• Monitor for symptoms including fever, severe sore throat, posterior cervical lymphadenopathy, and extreme fatigue over the next 4-6 weeks 4, 2
• Seek testing only if symptoms develop: Complete blood count with differential (looking for >40% lymphocytes and >10% atypical lymphocytes) plus heterophile antibody test 2

Practical Guidance on Contact

• There is no evidence-based recommendation to avoid contact with diagnosed mononucleosis patients if you're asymptomatic 4, 2
• Avoid sharing saliva through kissing, sharing drinks, utensils, or toothbrushes during the boyfriend's acute illness (first 4 weeks of symptoms) 2, 3
• Most transmission occurs before the index patient becomes symptomatic, so isolation after diagnosis has limited preventive value 3

Common Pitfall

The biggest mistake is ordering tests on asymptomatic contacts thinking it will guide exposure decisions—this wastes healthcare resources and provides false reassurance or unnecessary anxiety based on results that cannot predict who will develop disease 1, 7