Key messages

  • Primary cytomegalovirus (CMV) infection may cause a mononucleosis syndrome clinically indistinguishable from Epstein–Barr virus infection.
  • CMV is the most important cause of congenital viral infections in Australia. Some infected infants develop health problems.
  • Once a person becomes infected, they may develop a latent infection.
  • Prevention focuses on reducing the risk of CMV transmission to women who are pregnant and of childbearing age, and other people at risk of more serious infections.

Notification requirement for cytomegalovirus infection

Notification is not required.

Primary school and children’s service centres exclusion for cytomegalovirus infection

School exclusion is not required.

Infectious agent of cytomegalovirus infection

Cytomegalovirus (CMV), which is also designated as human herpesvirus 5 (HHV-5), is a member of the subfamily Betaherpesvirinae of the family Herpesviridae. Other members of the herpesvirus group include herpes simplex virus types 1 and 2, varicella–zoster virus (which causes chickenpox and shingles), and Epstein–Barr virus (which causes infectious mononucleosis, also known as glandular fever). These viruses share a characteristic ability to remain dormant within the body over a long period.

Identification of cytomegalovirus infection

Clinical features

Primary CMV infection of children and adults may cause a mononucleosis syndrome clinically indistinguishable from that caused by the Epstein–Barr virus (glandular fever). Features include fever, lymphadenopathy and mild hepatitis. More rare features include anaemia, thrombocytopaenia, pneumonitis, meningoencephalitis and Guillain-Barré syndrome. Many infections are asymptomatic, particularly those in young children.

Pregnancy

Healthy pregnant women are not at special risk for disease from CMV infection, but between 1 per cent and 5 per cent are infected for the first time during their pregnancy. Many women will already have been exposed to CMV.

When infected with CMV, most pregnant women have no symptoms, while a very few have a disease resembling mononucleosis. However, of those women who are infected for the first time during their pregnancy, approximately one in three will pass the CMV infection on to her developing unborn child. Reinfection or non-primary infection with CMV, however, still carries a substantial risk of transmission to the foetus (reported as high as 19.6 per cent). Although pre-existing maternal immunity reduces maternal–foetal transmission, the severity of congenital CMV disease is similar following primary or non-primary infection.

CMV remains the most important cause of congenital viral infections in Australia. For infants who are infected by their mothers before birth, two potential problems exist:

  • Generalised infection may occur, with symptoms ranging from moderate enlargement of the liver and spleen with jaundice, to stillbirth or neonatal/infant death. With supportive treatment, most infants with CMV disease survive. However, 80 per cent to 90 per cent will have complications within the first few years of life, which may include hearing loss, vision impairment and varying degrees of mental retardation.
  • Another 5 per cent to 10 per cent of infants who are infected but without symptoms at birth will subsequently have varying degrees of hearing and mental or coordination problems.

Immunosuppression

Other people at increased risk of severe infection include patients with impaired immunity due to HIV/AIDS infection, corticosteroid therapy, lymphoma or sarcoidosis. In these people, disease is usually due to the reactivation of previous infection. Manifestations include sight-threatening retinitis, pneumonitis, gastrointestinal ulceration and inflammation, and neurological disease particularly affecting the brain and spinal cord.

Diagnosis

CMV may be detected by virus isolation or polymerase chain reaction (PCR), usually from urine. Virus may also be detected in saliva, breast milk, semen and cervical secretions during primary and reactivated infection.

CMV causes typical ‘cytomegalic’ cells in tissue culture and characteristic histologic features in affected tissues. CMV antigens may be detected using rapid antigen tests. Serology is also available where recent infection is suggested by the identification of CMV IgM or a fourfold or greater rise in serum IgG titres to CMV from paired sera.

Isolation of CMV from culture does not necessarily imply recent infection, as CMV may be excreted for months to years following infection. Positive results for CMV from laboratory investigations should always be considered with clinical findings.

Incubation period of cytomegalovirus

The incubation period of sporadic cases of CMV usually cannot be determined. Perinatal infection develops 3–12 weeks after delivery. In adults with iatrogenic infection, illness usually occurs 3–8 weeks after blood transfusion and between 4 weeks and 4 months after organ transplantation.

Public health significance and occurrence of cytomegalovirus infection

Although infection with CMV is very common around the world, symptomatic disease is rare. The risk of severe or complicated CMV infection is increased in some groups, including:

  • developing infants during pregnancy
  • people with immunosuppression, such as organ transplant recipients, people infected with human immunodeficiency virus (HIV) and those being treated for cancer.

Serosurveys of adult populations worldwide have shown widespread evidence of previous CMV infection; seropositivity rates range from 40 per cent in highly developed countries to 100 per cent in developing countries.

The incidence peaks during the perinatal period, with a secondary peak among young adults in areas where perinatal infection is less common.

Reservoir of cytomegalovirus

Humans are the reservoir.

Mode of transmission of cytomegalovirus

CMV is excreted in urine, saliva, breast milk, cervical secretions and semen during primary and reactivated infections. CMV may be transmitted by:

  • transplacental infection of the foetus of a mother with primary, non-primary or reactivated infection
  • perinatal infection of neonates via infective maternal cervical secretions or breast milk
  • blood transfusion or organ transplantation
  • intimate exposure by mucosal contact with infective tissues, secretions or excretions.

CMV is not readily spread by casual contact but requires prolonged, intimate exposure for transmission. This can occur in settings such as childcare centres, where toddlers shed the virus in saliva and urine and thereby spread the infection among them.

Period of communicability of cytomegalovirus infection

CMV may be shed in the bodily fluids of any previously infected person, and thus may be found in urine, saliva, blood, tears, semen and breast milk. The shedding of virus may take place intermittently for months to years after primary infection without any detectable signs and without causing symptoms.

Neonatal infection in particular is associated with prolonged excretion. The period of excretion seems to be shorter in adults.

Susceptibility and resistance to cytomegalovirus infection

Once a person becomes infected, the virus may remain dormant in their body for life (latent infection). Recurrent disease rarely occurs unless the person's immune system is suppressed due to therapeutic drugs or disease.

Control measures for cytomegalovirus infection

Preventive measures

There is no vaccine available to protect against CMV infection.

Public health measures focus on reducing the risk of CMV transmission to pregnant women, women of childbearing age and other people at risk of more serious infections.

Women of childbearing age working in hospitals (especially obstetric and paediatric wards), childcare centres and preschools should practise strict infection control precautions and regard all body fluids as potentially infectious.

Pregnant women in a home setting should practise good personal hygiene, including handwashing with soap and water. They should also refrain from sharing food, eating utensils and drinking utensils with anyone. If a pregnant woman develops a mononucleosis-like illness, it is recommended that she be checked for CMV infection.

The CMV status of blood and organ donors should be matched to that of recipients wherever possible. If CMV-seropositive donors must be used for CMV-seronegative recipients, prophylactic use of hyperimmune immunoglobulin or antiviral drugs may be considered.

Control of case

There is no specific treatment recommended for primary CMV infection of normal hosts.

Immunosuppressed people with CMV retinitis or pneumonitis are usually treated in specialist centres with ganciclovir, foscarnet or cidofovir/probenecid. These drugs may also be of benefit for other complications of CMV infection.

The risk of congenital CMV infection after primary maternal CMV infection remains elevated for up to 4 years after seroconversion (the highest risk is in the first 2 years after seroconversion). The overall risk decreases to baseline 1 per cent risk by about 4 years after seroconversion. This information may be helpful in relation to the timing of a subsequent pregnancy.

Control of contacts

None required because of the high prevalence of asymptomatic virus shedders in the community.

Control of environment

Not applicable.

Outbreak measures for cytomegalovirus infection

Not applicable.

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