CYTOMEGALOVIRUS IN CHILDREN AND PROVIDERS: MORE COMMON THAN YOU THINK

Cytomegalovirus (CMV) infection in childhood is generally asymptomatic. It's importance lies in the ability of pre-school children to transmit the infection to parents and daycare providers who may be pregnant, with a risk of congenital infection in future offspring. CMV poses the greatest risk to developing fetuses, in some cases causing mental retardation and physical disabilities. In fact CMV is as common a cause of birth defects as the more widely known Down's syndrome. About 5,000 children born each year in the United States are mentally retarded and/or physically disabled as a result of CMV infection; an estimated 500 children in Canada are affected annually.

Infections are acquired in children during the birth process, through breast milk, and through contact with other children as well as through blood transfusions. Later in life infection is acquired through sexual contact. Infected infants and young children frequently transmit the virus to their mothers and to daycare staff. The greatest concern of course is that the offspring of a woman who develops CMV infection in pregnancy may develop congenital CMV. Studies from Sweden and the United States have shown that CMV infections are common in children and infants attending child daycare centers with rates of 9 - 72% compared with rates of 7 - 8% in children at home or in hospital. In a recent study conducted in Toronto child care centers, 17% of infants were documented to have CMV in their urine.

Most children and adults have no symptoms from CMV infection and are not harmed by the virus. In some cases CMV infections may present as a mononucleosis-like illness with fever, sore throat, fatigue and lymphadenopathy. The particular time one would like to avoid CMV infection, if possible, is during pregnancy. Newborn infants with CMV infection fall into two categories: those who are asymptomatic and those who are symptomatic. Approximately one in 100 infants is born with CMV infection but appears to be perfectly normal at birth. However, between 10 - 15% of these infants will develop disabilities later that occurred as a result of damage to the central nervous system. These disabilities may include hearing loss, developmental delay, psychomotor retardation and learning problems. Approximately 1 in 1000 babies will be symptomatic at birth. These infants may be born small for gestational age, have hepatosplenomegaly, microcephaly and may suffer neurological deficits such as mental retardation or deafness.    

 Rubella during pregnancy may be symptomatic with a typical viral exanthematous rash ± arthritis. CMV however usually does not produce any symptoms of illness so that the pregnant mother is unaware that she has been infected with CMV. The risks for congenital rubella infection in the fetus are clearly defined but the exact risks from CMV infection to the fetus are unknown. Also, Rubella infection is now much less common than previously because of vaccination protection. There is no vaccine currently available for CMV, although researchers are working on a vaccine, but it may take several years before one could be given routinely.  

Close person to person contact is the way CMV is usually spread. CMV may be found in body secretions including urine, saliva, feces, blood and blood products, semen and cervical secretions. There is also evidence that small amounts of CMV virus may be carried on inanimate objects such as toys, possibly contributing to spread among preschool children. Because people are exposed to CMV so often, most eventually develop CMV infection and become immune. This has been confirmed by recent Canadian data which have shown that two-thirds of health care providers in daycare centers have circulating CMV antibodies. Seronegative mothers of infected children are more likely than mothers of uninfected children to become infected (35-50% vs 2-11%).  

Women of childbearing age should be informed that CMV is widespread but the vast majority of infants of mothers infected during pregnancy are normal. Mothers should be informed that prevention of infection from infants and children in any home or occupational setting is best accomplished by observing good personal hygiene paticularily handwashing. Antibody testing for women who work with children is controversial. Canadian data suggests that there is sufficient risk posed by CMV that all daycare workers who are planning pregnancy should be screened for CMV status. Women found to be seropositive prior to conception can be reassured that there is minimal if any risk to future infants. For those found to be seronegative the case is not clear. Although no intervention strategy has been proven to reduce the risk, improving hygienic practice is currently advocated as the most important preventive measure. In the child care setting this includes careful handwashing after each contact with secretions or urine, decontamination of objects that become soiled by urine or secretion and sanitary procedures for diapering. These measures have been effective in hospital settings where the rates of CMV excretion are up to 20% among hospitalized infants (17% in daycare infants). Nurses taking care of these children on a continuous basis have annual seroconversion rates of 2-4% (12% conversion in daycare centers).  

No. The risk of CMV exposure to such children should be viewed in the context of the far greater exposure to many healthy children who are unrecognized shedders of CMV. In all child daycare centers, close attention should be given to personal hygiene such as handwashing after diaper changing or assistance in the bathroom. Pregnant women who work in settings where CMV is present should take reasonable precautions such as regular handwashing to minimize their exposure to CMV. All women working in institutions and childcare centers must be informed about CMV infection and educated regarding measures that can reduce the likelihood of CMV and other contagious agents.   CMV vaccine? A vaccine ( which is currently being worked on) is badly needed for susceptible women of child-bearing age!  

Reference

Ford-Jones EL, Pediatr Infect Dis J 15: 507-14,1996.