CMV, or cytomegalovirus, spreads through direct contact with infected body fluids, including saliva, urine, blood, tears, semen, and breast milk. Over half of adults in the United States have been infected with CMV by age 40, and most never realize it because the virus rarely causes noticeable symptoms in healthy people.
The Body Fluids That Carry CMV
CMV travels in a wide range of body fluids. The most common routes of everyday transmission involve saliva and urine, but the virus also spreads through blood, tears, semen, breast milk, and genital secretions. Any activity that puts you in contact with these fluids from an infected person can lead to transmission: kissing, sexual contact, sharing utensils or drinks, or handling items contaminated with saliva or urine.
CMV is not considered highly contagious in the way a cold or flu is. You won’t catch it from being in the same room as someone or from brief casual contact. It requires direct exposure to body fluids, which is why it tends to spread among people in close, sustained contact, like household members or children in group care settings.
Young Children Are the Most Common Source
The single biggest source of CMV infection for adults, particularly pregnant women, is contact with the saliva and urine of young children. Up to 70% of healthy children between ages one and three in childcare settings actively shed the virus in their saliva and urine, even when they appear perfectly healthy. This shedding can continue for months after initial infection. In one study of children with confirmed CMV, the median duration of viral shedding in saliva was 20 months, and about a third of children shed the virus intermittently over even longer periods.
This makes daycare centers, preschools, and home childcare environments high-risk settings for adult exposure. Diaper changing, wiping a toddler’s nose, sharing food or utensils, and getting kissed on the mouth by a young child are all common ways the virus passes from children to adults. People who work closely with young children have a higher risk of CMV infection than the general population, and contact with children’s saliva or urine is a major cause of CMV infection in pregnant people specifically.
Sexual Contact and Intimate Relationships
CMV spreads through sexual contact because the virus is present in semen, vaginal secretions, and saliva. Both oral and penetrative sex can transmit the virus. Since most people who carry CMV have no symptoms, a partner may be shedding the virus without either person knowing. This is one of the reasons CMV is so widespread in the adult population: it circulates quietly through normal intimate contact over a lifetime.
From Mother to Baby During Pregnancy
A pregnant person who becomes infected with CMV can pass the virus to their baby. The virus crosses from the mother’s blood through the placenta to the fetus. This can happen during a first-time CMV infection or during a reactivation of a previous infection. Congenital CMV, as this is called, is one of the leading infectious causes of birth defects and can result in hearing loss, developmental delays, or other complications in the newborn. A baby can also pick up CMV by contacting the mother’s genital secretions during delivery or through breast milk after birth.
Organ Transplants and Blood Transfusions
CMV can be transmitted through transplanted organs, bone marrow, stem cells, and blood transfusions. This is a particular concern for transplant recipients because the immune-suppressing medications they take to prevent organ rejection also make it harder for their body to control CMV. The highest-risk scenario is when a person who has never had CMV receives an organ from a donor who carries the virus.
Certain transplant types carry greater risk, including lung, liver, kidney, and small bowel transplants. Before any transplant, medical teams test both the recipient and the donor for CMV. When possible, providers match CMV-negative recipients with CMV-negative donors. For those at high risk, preventive antiviral treatment may begin immediately after surgery, and regular lab monitoring helps catch any viral reactivation early.
How CMV Stays in the Body
Once you’re infected with CMV, the virus never fully leaves. It enters a dormant state and remains in your body for life. In healthy people, the immune system keeps the virus suppressed indefinitely, and most people never experience any problems from it. But the virus can reactivate, particularly if the immune system becomes weakened due to illness, medication, or major physiological stress. During reactivation, a person can shed the virus in body fluids again and potentially pass it to others.
This is why CMV is so remarkably common. People can shed the virus without symptoms, for months at a time, and the virus persists in the population through a combination of new infections and periodic reactivation in people who were infected years or decades earlier.
Most People Never Know They Have It
After exposure, the incubation period for CMV is typically between 3 and 12 weeks. Most children and adults who become infected develop no symptoms at all. When symptoms do appear in healthy adults, they tend to resemble a mild, prolonged flu: fatigue, low-grade fever, sore throat, and swollen glands. These symptoms usually resolve on their own without treatment and are often attributed to other common illnesses.
The people who face real danger from CMV are those with weakened immune systems (transplant recipients, people with HIV, those on chemotherapy) and developing fetuses. For everyone else, CMV is one of those infections the body handles quietly in the background.
Reducing Your Risk
Because CMV spreads through body fluids, basic hygiene practices make a meaningful difference. If you’re pregnant or planning to become pregnant and you spend time around young children, the most important steps are straightforward: wash your hands thoroughly with soap and water after changing diapers, wiping a child’s nose or drool, or handling toys that have been in a child’s mouth. Avoid sharing food, drinks, or utensils with young children, and don’t kiss them on or near the mouth.
These precautions feel unnatural for parents and caregivers, but they’re effective at reducing exposure to the virus during the window when it matters most. For the general population, there’s no vaccine for CMV and no practical way to avoid all exposure over a lifetime, which is why most adults eventually become infected. The goal isn’t to prevent all infection but to reduce risk during the specific periods when CMV can cause serious harm.