Clinical Overview

For most healthy people who acquire cytomegalovirus (CMV) after birth, there are few symptoms and no long-term health consequences. Some people who acquire CMV infection may experience a mononucleosis-like syndrome with prolonged fever and hepatitis. Once a person becomes infected, the virus establishes lifelong latency and may reactivate intermittently. Disease from reactivation of CMV infection rarely occurs unless the person's immune system is suppressed due to therapeutic drugs or disease.

For most people, CMV infection is not a serious health problem. However, certain groups are at high risk for serious complications from CMV infection:

1. Infants infected in utero (congenital CMV infection)
2. Very low birth weight and premature infants
3. People with compromised immune systems, such as from organ and bone marrow transplants, and people infected with human immunodeficiency virus (HIV)

Characteristics of the Virus

CMV is a herpesvirus. This group of viruses include herpes simplex virus types 1 and 2, varicella-zoster virus, and Epstein-Barr virus. These viruses share a characteristic ability to establish lifelong latency. After initial infection, which may cause few symptoms, CMV becomes latent, residing in cells without causing detectable damage or clinical illness.

People who are infected with CMV sometimes shed the virus in body fluids, such as urine, saliva, blood, tears, semen, and breast milk. The shedding of virus may occur intermittently, without any detectable signs, and without causing symptoms. However, in people who are severely immunocompromised by medication or disease, viral reactivation may lead to symptomatic disease.

Transmission

CMV is transmitted by direct contact with infectious body fluids, such as urine or saliva. CMV can be transmitted sexually and through transplanted organs and blood transfusions.

CMV can be transmitted to infants through contact with maternal genital secretions during delivery or through breast milk. Healthy infants and children who acquire CMV after birth generally have few, if any, symptoms or complications from the infection. Women who are infected with CMV can still breastfeed infants born full-term.

Although the virus is not highly contagious, it has been shown to spread among household members and young children in daycare centers.

Risk of CMV Infection

CMV infects people of all ages. In the United States; nearly one in three children are already infected with CMV by age 5 years. By 40 years, over half of adults have been infected with CMV.

Childcare workers

People who care for or work closely with young children may be at greater risk of CMV infection than other people because CMV infection is common among young children. By age 5 years, one in three children have been infected with CMV, usually from breastfeeding or contact with other young children. Although young children with CMV infection generally have no symptoms, CMV can be present in their body fluids for months after they first become infected. Regular hand washing, especially after contact with body fluids of young children, is commonly recommended to avoid spread of infections, including CMV.

Pregnant women

In the United States, nearly half of women have already been infected with CMV before their first pregnancy. Of women who have never had a CMV infection, it is estimated that 1-4% of them will have a primary infection during pregnancy.

A woman who has a primary CMV infection during pregnancy is more likely to pass CMV to her fetus than a women who is reinfected or has a reactivation of the latent virus during pregnancy. However, in the United States, 50-75% of congenital CMV infections occur among infants born to mothers already infected with CMV, who either had a reinfection or a reactivation during pregnancy.

Routine screening for primary CMV infection during pregnancy is not recommended in the United States. Most laboratory tests currently available cannot conclusively detect if a primary CMV infection occurred during pregnancy. This makes it difficult to counsel pregnant women about the risk to their fetuses. The lack of a proven treatment to prevent or treat infection of the fetus reduces the potential benefits of prenatal screening.

Very low birth weight and premature infants

There are no recommendations against breastfeeding by mothers who are CMV-seropositive. However, premature infants (born <30 weeks gestational age and <1500g) who acquire CMV from breast milk may be at risk of developing a late-onset sepsis-like syndrome. The potential benefits of human milk versus the risk of CMV transmission should be considered when making a decision about breastfeeding of very low birth weight infants (birth weight <1500 g) by mothers known to be CMV-seropositive. Freezing and pasteurization of breast milk can decrease the risk of transmission; however, freezing does not eliminate the risk of transmission.

Diagnosing CMV

Primary CMV infections usually go unrecognized because most people are asymptomatic or do not have specific symptoms. Primary CMV infection should be suspected if a woman

• Has symptoms of infectious mononucleosis but has negative test results for Epstein-Barr virus, or
• Shows signs of hepatitis, but has negative test results for hepatitis A, B, and C.

CMV may be detected by viral culture or polymerase chain reaction (PCR) of infected blood, urine, saliva, cervical secretions, or breast milk.

CMV infection is usually diagnosed using serologic testing. Serum samples collected one to three months apart can be used to diagnose primary infection. Seroconversion (1st sample IgG negative, 2nd sample IgG positive) is clear evidence for recent primary infection. However, diagnosis of CMV infection between birth and one year can be complicated by the presence of maternal CMV IgG. For more information, see Interpretation of Laboratory Tests.

Treatment and Management

• No treatment is currently indicated for CMV infection in healthy people.
• Antiviral treatment is used for people with compromised immune systems who have either sight-related or life-threatening illnesses due to CMV infection.
• For congenital CMV treatment options, see Congenital CMV Infection.

Prevention

Regular handwashing, especially after contact with body fluids of young children, is commonly recommended to avoid spread of infections, including CMV.

Healthcare providers should follow standard precautions.

Vaccines are still in the research and development stage.

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