Cytomegalovirus (CMV), also known as Human Herpesvirus 5, is a common virus belonging to the herpesvirus family. Most people become infected with CMV at some point in their lives; over half of adults have evidence of past infection by age 40. For healthy individuals, this infection is usually asymptomatic or causes a mild, flu-like illness that quickly resolves. However, CMV remains a concern because it can cause serious complications for developing fetuses and people with weakened immune systems. The duration of contagiousness depends on the virus’s behavior and the individual’s health status.
Primary Transmission Routes
CMV is transmitted through direct contact with various infected bodily fluids. The virus can be found in saliva, urine, blood, tears, semen, and breast milk, making close personal contact the primary method of spread. Transmission often occurs in childhood settings, where young children frequently expose others to the virus through their saliva and urine.
For adults, sexual contact represents a major route of transmission because the virus is present in semen and cervical secretions. A mother can also pass the virus to her child either during pregnancy (congenital transmission) or at the time of birth through contact with genital secretions. Less common routes include receiving infected blood products or transplanted organs.
Understanding Viral Shedding
Contagiousness in CMV is directly linked to viral shedding. Shedding is the mechanism by which the virus replicates and is released from the body into fluids like urine and saliva, making the infected person capable of passing the virus to others. Like all herpesviruses, CMV establishes lifelong latency after the initial infection.
This latency means the virus remains dormant within the host’s cells, causing no symptoms and no active shedding. However, CMV can reactivate and begin shedding intermittently, sometimes years after the initial infection. Reactivation can be triggered by various factors, often occurring without any noticeable illness or symptoms in the person shedding the virus. This silent shedding makes the virus difficult to contain.
How Long CMV is Shed (Duration of Contagiousness)
The duration of contagiousness varies depending on the age and immune status of the infected person. Children, particularly those who acquired the infection congenitally or very early in life, are the primary source of prolonged viral shedding. These infants and toddlers often shed high concentrations of CMV in their urine and saliva for months and sometimes for several years.
Congenitally infected children may continue to shed the virus until they are between two and five years old, and shedding can persist even longer. This prolonged period explains why close contact with young children in daycare or household settings poses a risk for transmission.
In contrast, healthy adults and older children who experience a primary CMV infection shed the virus for a shorter and less concentrated period. Following a first-time infection, shedding in healthy older individuals usually lasts for several weeks or a few months, commonly falling within a range of two to six months. The immune system is effective at suppressing the virus back into its latent state quickly.
However, in people with compromised immune systems, such as transplant recipients or those with HIV, CMV shedding can be much more persistent and recurrent. Their weakened ability to control the virus allows it to reactivate and be shed for extended and unpredictable periods.
Essential Prevention Strategies
Since young children are the primary source of prolonged viral shedding, prevention strategies focus heavily on hygiene practices around them. The most effective measure for reducing the risk of transmission is thorough hand hygiene. This involves washing hands with soap and water for 15 to 20 seconds, especially after contact with a child’s body fluids.
It is important to wash hands after changing diapers, wiping a child’s nose or mouth, or handling toys that have been in a child’s mouth. People, especially those who are pregnant, should avoid sharing food, drinks, or eating utensils with young children. They should also refrain from activities that involve direct contact with a child’s saliva, such as kissing a child directly on the mouth.
Cleaning surfaces and items contaminated with urine or saliva limits environmental spread. These simple, actionable steps are important because the virus can remain viable on hands and surfaces long enough to be transferred. Consistent adherence to these hygiene protocols significantly lowers the risk of acquiring CMV infection from a person who is actively shedding the virus.