Being CMV positive means your blood test shows you have been infected with cytomegalovirus at some point in your life. For the vast majority of people, this is a completely unremarkable finding. Most CMV-positive individuals never had noticeable symptoms and will never develop problems from the virus. However, CMV status matters in specific situations: pregnancy, organ transplantation, and any condition that weakens the immune system.
What the Test Results Mean
CMV testing typically looks for two types of antibodies in your blood: IgG and IgM. A positive CMV IgG result means you were infected with the virus at some point during your life, but it doesn’t tell you when. It could have been last year or decades ago. This is the result most people get when they’re told they’re “CMV positive.”
A positive IgM result is trickier. IgM antibodies usually appear during a newer infection, but they can also show up when an old infection reactivates. So a positive IgM alone can’t confirm a brand-new (primary) infection. When doctors need to distinguish a first-time infection from a reactivation, they combine IgM results with something called IgG avidity testing. Low avidity alongside a positive IgM is considered reliable evidence of a primary infection, which matters most during pregnancy.
How CMV Spreads and Who Gets It
CMV spreads through contact with infected body fluids: saliva, urine, breast milk, blood, semen, and vaginal fluids. It can also be transmitted through organ transplantation and blood transfusion. The virus is extremely common, and most people pick it up without realizing it.
Young children are major drivers of transmission. Kids between ages 1 and 2 shed the virus at especially high rates because they’re mobile, still in diapers, and prone to drooling. Children in day care settings shed CMV in their urine for an average of 13 months and in oral secretions for about 7 months. Congenitally infected children shed even longer: 100% are still shedding at age 1, and 73% continue through age 4. Adults who catch a new infection typically stop shedding within about six months.
Why Most People Never Notice It
Most people with CMV show no signs or symptoms and never realize they’ve been infected. When symptoms do appear in healthy individuals, they’re mild and generic: fever, sore throat, fatigue, swollen glands. Occasionally CMV causes something resembling mononucleosis or mild liver inflammation. These episodes resolve on their own without treatment.
The reason CMV stays quiet is that a healthy immune system keeps the virus in check. After the initial infection clears, CMV doesn’t actually leave your body. It settles into certain immune cells (specifically, early-stage bone marrow cells) and goes dormant. The virus essentially wraps its genetic material tightly and shuts down, kept silent by your body’s molecular machinery. You carry it for life, but your immune system acts as a constant guard.
When CMV Becomes Dangerous
CMV causes serious problems in two main groups: people with weakened immune systems and developing fetuses.
For transplant recipients, people undergoing chemotherapy, or those with advanced HIV, the immune system can no longer keep the dormant virus suppressed. Reactivation is triggered by inflammation, infection, injury, or the immune-suppressing drugs used after transplantation. When the virus wakes up in these patients, it can cause disease in the eyes, lungs, liver, esophagus, stomach, and intestines. Doctors monitor these patients with regular blood tests and start antiviral treatment either when the virus is detected in the blood (before symptoms appear) or when organ disease develops.
Healthy people whose CMV reactivates generally don’t need treatment. Their immune system handles the flare-up the same way it handled the original infection.
CMV Positive During Pregnancy
This is where CMV status carries the most weight for otherwise healthy people. If you’re CMV positive before becoming pregnant, your baby has some protection from your existing antibodies. The concern is a primary (first-time) infection during pregnancy, when there are no pre-existing antibodies to buffer the fetus.
With a primary maternal CMV infection, the overall risk of transmission to the baby is approximately 30 to 40%. That risk varies by trimester: about 30% in the first trimester, 34 to 38% in the second, and 40 to 72% in the third. Infections transmitted earlier in pregnancy tend to cause more severe outcomes because the baby’s organs are still forming. Congenital CMV can lead to hearing loss, developmental delays, and vision problems, though many infected newborns have no symptoms at birth.
Practical prevention during pregnancy focuses on avoiding contact with young children’s saliva and urine. That means washing your hands after diaper changes or wiping a child’s face, not sharing food or utensils with toddlers, and avoiding kissing young children on or near the mouth.
Newborn Screening for CMV
Newborn screening for congenital CMV is expanding in the United States, though it’s not yet universal. Minnesota began screening all newborns in 2023, and New York State currently screens all newborns as well. Connecticut passed legislation in 2023 mandating universal screening, expected to start in 2025. Federal legislation called the “Stop CMV Act” has been introduced in both the Senate and the House, which would authorize funding for states to administer congenital CMV testing.
Many states currently use a targeted approach, testing only babies who fail their newborn hearing screen or have other risk factors. The American Academy of Otolaryngology has endorsed universal screening, while the American Academy of Audiology supports targeted screening. The American Academy of Pediatrics has not yet taken a formal position but is expected to address the question in updated guidelines.
What to Do With a CMV Positive Result
If you’re a healthy adult who tested CMV positive on routine bloodwork or during a pre-pregnancy workup, the result simply means you’ve been exposed at some point. No treatment is needed, and no lifestyle changes are necessary outside of pregnancy.
If you tested positive during pregnancy, the key question is whether this is a new infection or an old one. Your doctor will look at whether IgM is present, the IgG avidity, and sometimes repeat testing over a few weeks to see if antibody levels are changing. A long-standing infection (high IgG avidity, no IgM) is far less concerning than a new one.
If you’re preparing for an organ transplant or starting immunosuppressive therapy, your CMV status becomes part of your medical planning. A CMV-positive recipient carries dormant virus that could reactivate once their immune system is suppressed. A CMV-negative recipient receiving an organ from a CMV-positive donor faces a different risk: a brand-new infection without any prior immunity. In both cases, the medical team monitors for the virus and intervenes early if it appears in the blood.