GENERAL INFORMATION
Cytomegalovirus, or CMV, is found universally throughout all
geographic locations and socioeconomic groups, and infects
between 50% and 85% of adults in the United States by 40 years
of age. CMV is also the virus most frequently transmitted to a
developing child before birth. CMV infection is more widespread
in developing countries and in areas of lower socioeconomic
conditions. For most healthy persons who acquire CMV after
birth there are few symptoms and no long-term health
consequences. Some persons with symptoms experience a
mononucleosis-like syndrome with prolonged fever, and a mild
hepatitis. Once a person becomes infected, the virus remains
alive, but usually dormant within that person's body for life.
Recurrent disease rarely occurs unless the person's immune
system is suppressed due to therapeutic drugs or disease.
Therefore, for the vast majority of people, CMV infection is not
a serious problem.
However, CMV infection is important to certain high-risk
groups. Major areas of concern are (1) the risk of infection to
the unborn baby during pregnancy, (2) the risk of infection to
people who work with children, and (3) the risk of infection to
the immunocompromised person, such as organ transplant
recipients and persons infected with human immunodeficiency
virus (HIV).
CHARACTERISTICS OF THE VIRUS
CMV is a member of the herpesvirus group, which includes
herpes simplex virus types 1 and 2, varicella-zoster virus
(which causes chickenpox), and Epstein-Barr virus (which causes
infectious mononucleosis). These viruses share a characteristic
ability to remain dormant within the body over a long period.
Initial CMV infection, which may have few symptoms, is always
followed by a prolonged, inapparent infection during which the
virus resides in cells without causing detectable damage or
clinical illness. Severe impairment of the body's immune system
by medication or disease consistently reactivates the virus from
the latent or dormant state.
Infectious 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, without any detectable
signs, and without causing symptoms.
TRANSMISSION AND PREVENTION
Transmission of CMV occurs from person to person.
Infection requires close, intimate contact with a person
excreting the virus in their saliva, urine, or other bodily
fluids. CMV can be sexually transmitted and can also be
transmitted via breast milk, transplanted organs, and rarely
from blood transfusions.
Although the virus is not highly contagious, it has been
shown to spread in households and among young children in day
care centers. Transmission of the virus is often preventable
because it is most often transmitted through infected bodily
fluids that come in contact with hands and then are absorbed
through the nose or mouth of a susceptible person. Therefore,
care should be taken when handling children and items like
diapers. Simple hand washing with soap and water is effective in
removing the virus from the hands.
CMV infection without symptoms is common in infants and young
children; therefore, it is unjustified and unnecessary to
exclude from school or an institution a child known to be
infected. Similarly, hospitalized patients do not need separate
or elaborate isolation precautions.
Screening children and patients for CMV is of questionable
value. The cost and management of such procedures are
impractical. Children known to have CMV infection should not be
singled out for exclusion, isolation, or special handling.
Instead, staff education and effective hygiene practices are
advised in caring for all children.
CIRCUMSTANCES IN WHICH CMV INFECTION COULD BE A PROBLEM
Pregnancy
The incidence of primary (or first) CMV infection in
pregnant women in the United States varies from 1% to 3%.
Healthy pregnant women are not at special risk for disease from
CMV infection. When infected with CMV, most women have no
symptoms and very few have a disease resembling mononucleosis.
It is their developing unborn babies that may be at risk for
congenital CMV disease. CMV remains the most important cause of
congenital (meaning from birth) viral infection in the United
States. For infants who are infected by their mothers before
birth, two potential problems exist:
- Generalized infection may occur in the infant, and
symptoms may range from moderate enlargement of the liver
and spleen (with jaundice) to fatal illness. With supportive
treatment most infants with CMV disease usually survive.
However, from 80% to 90% will have complications within the
first few years of life that may include hearing loss,
vision impairment, and varying degrees of mental
retardation.
- Another 5% to 10% of infants who are infected but without
symptoms at birth will subsequently have varying degrees of
hearing and mental or coordination problems.
However, these risks appear to be almost exclusively
associated with women who previously have not been infected
with CMV and who are having their first infection with
the virus during pregnancy. Even in this case, two-thirds of the
infants will not become infected, and only10% to 15% of the
remaining third will have symptoms at the time of birth. There
appears to be little risk of CMV-related complications for women
who have been infected at least 6 months prior to conception.
For this group, which makes up 50% to 80% of the women of
child-bearing age, the rate of newborn CMV infection is 1%, and
these infants appear to have no significant illness or
abnormalities.
The virus can also be transmitted to the infant at delivery
from contact with genital secretions or later in infancy through
breast milk. However, these infections usually result in little
or no clinical illness in the infant.
To summarize, during a pregnancy when a woman who has
never had CMV infection becomes infected with CMV, there is
a potential risk that after birth the infant may have
CMV-related complications, the most common of which are
associated with hearing loss, visual impairment, or diminished
mental and motor capabilities. On the other hand, infants and
children who acquire CMV after birth have few, if any,
symptoms or complications.
Recommendations for pregnant women with regard to CMV
infection:
- Throughout the pregnancy, practice good personal hygiene,
especially handwashing with soap and water, after contact
with diapers or oral secretions (particularly with a child
who is in day care).
- Women who develop a mononucleosis-like illness during
pregnancy should be evaluated for CMV infection and
counseled about the possible risks to the unborn child.
- Laboratory testing for antibody to CMV can be performed to
determine if a women has already had CMV infection.
- Recovery of CMV from the cervix or urine of women at or
before the time of delivery does not warrant a cesarean
section.
- The demonstrated benefits of breast-feeding outweigh the
minimal risk of acquiring CMV from the breast-breeding
mother.
- There is no need to either screen for CMV or exclude
CMV-excreting children from schools or institutions because
the virus is frequently found in many healthy children and
adults.
People Who Work with Infants and Children
Most healthy people working with infants and children
face no special risk from CMV infection. However, for women of
child-bearing age who previously have not been infected with
CMV, there is a potential risk to the developing unborn child
(the risk is described above in the Pregnancy section). Contact
with children who are in day care, where CMV infection is
commonly transmitted among young children (particularly
toddlers), may be a source of exposure to CMV. Since CMV is
transmitted through contact with infected body fluids, including
urine and saliva, child care providers (meaning day care
workers, special education teachers, therapists, as well as
mothers) should be educated about the risks of CMV infection and
the precautions they can take. Day care workers appear to be at
a greater risk than hospital and other health care providers,
and this may be due in part to the increased emphasis on
personal hygiene in the health care setting.
Recommendations for individuals providing care for infants
and children:
- Female employees should be educated concerning CMV, its
transmission, and hygienic practices, such as hand-washing,
which minimize the risk of infection.
- Susceptible non-pregnant women working with infants and
children should not routinely be transferred to other work
situations.
- Pregnant women working with infants and children should be
informed of the risk of acquiring CMV infection and the
possible effects on the unborn child.
- Routine laboratory testing for CMV antibody in female
workers is not recommended, but can be performed to
determine their immune status.
Immunocompromised Patients
Primary (or the initial) CMV infection in the
immunocompromised patient can cause serious disease. However,
the more common problem is the reactivation of the dormant
virus. Infection with CMV is a major cause of disease and death
in immunocompromised patients, including organ transplant
recipients, patients undergoing hemodialysis, patients with
cancer, patients receiving immunosuppressive drugs, and
HIV-infected patients. Pneumonia, retinitis (an infection of the
eyes), and gastrointestinal disease are the common
manifestations of disease. Because of this risk, exposing
immunosuppressed patients to outside sources of CMV should be
minimized. Whenever possible, patients without CMV infection
should be given organs and/or blood products that are free of
the virus.
DIAGNOSIS OF CMV INFECTION
Most infections with CMV are not diagnosed because the virus
usually produces few, if any, symptoms and tends to reactivate
intermittently without symptoms. However, persons who have been
infected with CMV develop antibodies to the virus, and these
antibodies persist in the body for the lifetime of that
individual. A number of laboratory tests that detect these
antibodies to CMV have been developed to determine if infection
has occurred and are widely available from commercial
laboratories. In addition, the virus can be cultured from
specimens obtained from urine, throat swabs, and tissue samples
to detect active infection.
CMV should be suspected if a patient:
- has symptoms of infectious mononucleosis but has negative
test results for mononucleosis and Epstein Barr virus, or,
- shows signs of hepatitis, but has negative test results
for hepatitis A, B, and C.
For best diagnostic results, laboratory tests for CMV
antibody should be performed by using paired serum samples. One
blood sample should be taken upon suspicion of CMV, and another
one taken within 2 weeks. A virus culture can be performed at
any time the patient is symptomatic.
Laboratory testing for antibody to CMV can be performed to
determine if a woman has already had CMV infection. However,
routine laboratory testing of all pregnant women is costly and
the need for testing should therefore be evaluated on a
case-by-case basis.
Serologic Testing
The enzyme-linked immunosorbent assay (or ELISA) is the
most commonly available serologic test for measuring antibody to
CMV. The result can be used to determine if acute infection,
prior infection, or passively acquired maternal antibody in an
infant is present. Other tests include various fluorescence
assays, indirect hemagglutination, and latex agglutination.
An ELISA technique for CMV-specific IgM is available, but may
give false-positive results unless steps are taken to remove
rheumatoid factor or most of the IgG antibody before the serum
sample is tested. Because CMV-specific IgM may be produced in
low levels in reactivated CMV infection, its presence is not
always indicative of primary infection. Only virus recovered
from a target organ, such as the lung, provides unequivocal
evidence that the current illness is caused by acquired CMV
infection. If serologic tests detect a positive or high
titer of IgG, this result should not automatically be
interpreted to mean that active CMV infection is present.
However, if antibody tests of paired serum samples show a
fourfold rise in IgG antibody and a significant level of IgM
antibody, meaning equal to at least 30% of the IgG value, or
virus is cultured from a urine or throat specimen, the findings
indicate that an active CMV infection is present.
TREATMENT
Currently, no treatment exists for CMV infection in the
healthy individual. Antiviral drug therapy is now being
evaluated in infants. Ganciclovir treatment is used for patients
with depressed immunity who have either sight-related or
life-threatening illnesses. Vaccines are still in the research
and development stage.
ADDITIONAL INFORMATION
The Biomedical Research Institute of the St. Paul's
Children's Hospital, which no longer conducts research on CMV,
has published a brochure titled CMV: Diagnosis, Prevention,
and Treatment that has been made available for distribution
by CDC. This brochure can be obtained by writing to:
Viral Exanthems and Herpesvirus Branch
DVRD/NCID
Mail Stop A-15
Centers for Disease Control and Prevention
Atlanta, GA 30333
or by calling the Branch at 404-639-1338.
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