Transmission of CMV is very rare through casual contact. CMV is spread from one person to another, usually by direct and prolonged contact with bodily fluids, including saliva, urine, and breast milk.
CMV is common among healthy children one to three years of age who attend daycare and can easily spread the CMV virus among their peers. In the United States, nearly one in three children are already infected with CMV by 5 years of age. CMV is not generally harmful to these children and most do not exhibit signs or symptoms of infection.
Contact with the saliva or urine of young children is a major cause of CMV infection among pregnant women, especially mothers, daycare workers, preschool teachers, therapists, and nurses. Women who are pregnant, or plan to become pregnant, who have close contact with young children should practice standard hygiene procedures to prevent against congenital CMV. Make sure to wash your hands after:
- Changing diapers
- Feeding a child
- Wiping a child’s nose or mouth
- Handling a child’s toy
Although less common than exposure to a child’s urine or saliva, another possible means of infection is through sexual contact with a CMV infected partner.
Types of Transmission
Transmission During Pregnancy
CMV can be transmitted to the unborn child from a mother with a primary or a recurrent CMV infection. When a baby catches CMV prior to birth, it is known as a congenital CMV infection. Approximately 90% of all infants who are infected with CMV prior to delivery are born without symptoms of the virus; however, the remaining ten percent (10%) will have varying degrees of abnormalities.
Transmission During Birth
CMV can be transmitted to newborns via contact with maternal genital secretions during delivery or through breast milk. However, infections that occur through these routes usually result in little or no clinical illness in the newborn, unless the newborn is very premature.
Transmission During Breastfeeding
There are no recommendations against breastfeeding by mothers who are shedding CMV. The potential benefits of human milk versus the risk of CMV transmission should be considered when making a decision about breastfeeding for very low birth weight newborns (birth weight <1500 g) by mothers known to have an active CMV infection. Preterm newborns, <1000g birth weight and <30 weeks gestational age, may be at high risk of an acquired (after birth, in the newborn period) symptomatic CMV infection and may present a sepsis-like syndrome. Freezing and pasteurization of breast milk can decrease the risk of CMV transmission; however, freezing does not eliminate the risk altogether.
People with an active CMV infection can sometimes shed the virus in their body fluids, such as urine, saliva, blood, tears, semen, and breast milk. The shedding of CMV can happen without any obvious signs and without causing any visible symptoms.
Types of CMV Infections
A primary CMV infection is the first time that someone contracts CMV. People with a primary CMV infection will have no pre-existing immunity to the virus.
Primary CMV infection will impact one to four percent (1-4%) of pregnancies and can result in birth defects and developmental disabilities. Usually, there is less risk of CMV-related complications, illness, or abnormalities in babies with mothers infected prior to pregnancy.
A recurrent CMV infection is when a previous CMV infection that has been considered dormant becomes active again. A recurrent infection will rarely cause visible symptoms because the body has pre-existing immunity to the virus. CMV reactivation can occur when a person's immune system is suppressed due to stress, disease, hospitalizations, or certain therapeutic drugs.
If you have already been exposed to CMV, your body has antibodies against the virus. If you are pregnant, these antibodies, along with other immune factors, appear to protect the baby from the more serious illnesses due to a primary CMV infection.
Reinfection is a new infection with a different strain of the CMV virus. This type of infection is very unusual and its consequences are unknown at this time.