Perinatal cytomegalovirus infection in man

Human Breast Milk-acquired Cytomegalovirus Infection: Certainties, Doubts and Perspectives

Breast Milk (BM) is the best source of nutrition for newborns, especially if premature. In fact, its beneficial impact on short- and the long-term neonatal outcome has was deeply described. Unfortunately, BM could not be always so safe, especially due to the possible presence of maternal viruses that can be shed and transferred to the breastfed neonate. Among these, Cytomegalovirus (CMV) can potentially lead to a serious and acute illness, mostly in case of low gestational age. Some studies also report the association of CMV-acquired infection to an increased risk of structural and functional brain modifications and neurological impairment. Due to these reasons, a strategy to remove CMV from BM with a minimal or absent impact on its beneficial components would be desirable. Up to now, pasteurization, freezing, ultraviolet- C or microwave irradiation are the available techniques; they show different levels of efficacy and variable effects on BM composition, even if many studies are still needed to fully clarify these implications. In this review, we provide an update of the current evidence about these topics. We focus on the factors promoting CMV shedding through BM; moreover, the possible occurrence of a severe disease in preterm neonates is also described. Finally, we investigate the potential effects showed on BM properties by the strategies that prevent or reduce viral transmission, therefore influencing newborns' health, and the new techniques which could show a relevant role in the next future, such as metabolomics.

Seroepidemiologic study of human cytomegalovirus in pregnant women in Valiasr Hospital of Kazeroon, Fars, Iran

BACKGROUND

Cytomegalovirus (CMV) is a common opportunistic infection among HIV-infected individuals, a major source of serious complications among organ-transplant recipients, and a leading cause of hearing loss, vision loss, and mental retardation among congenitally infected children. Women infected for the first time during pregnancy are especially likely to transmit CMV to their fetuses.

OBJECTIVE

In this study, it was aimed to determine the rate of CMV seroprevalence in pregnant women, the prevalence of maternal CMV infection and also the incidence of congenital CMV infection in their newborns in the Kazeroon, south of Iran.

METHODS

Between January 2007 and July 2007, all (n = 1472) pregnant women who attended the obstetric ward of Valiasr hospital in Kazeroon for delivery, were enrolled in this study, and according to the presence or absence of anti CMV-IgM and CMV-IgG, were classified as seropositive, seronegative and having active maternal CMV infection. Differentiation of primary and recurrent CMV infection in women with both CMV-IgM (+) and CMV-IgG (+) antibody was determined by the avidity index (AI) of anti-CMV IgG.

RESULTS

The rate of seropositivity was found as 97.69% and the rate of seronegativity as 2.31% in pregnant women. The prevalence of active maternal CMV infection was found as 4.35% and among these pregnant women, the incidence of primary and recurrent maternal CMV infection was 34.4% and 65.6% respectively.

CONCLUSION

Seroprevalence rate of CMV in pregnant women is high and most infections are recurrent. Thus, it does not seem to be cost-effective to screen all pregnant women for CMV infection, as in the other countries with high seropositivity rate.

Natural history of perinatal cytomegaloviral infection

Epidemiological data presented here indicate that cytomegaloviral (CMV) infection is one of the most common perinatal infections found in human beings. Transmission to the offspring occurs in utero at birth and postnatally. Intrauterine infection results from primary or recurrent maternal involvement, the latter being more common in populations where infection is initially acquired during childhood or adolescence, such as in low socioeconomic settings. Congenital infection is usually subclinical with either type of maternal involvement but primary infection has a greater tendency to produce disease in the fetus. About 20% of the offspring infected in utero are damaged, infrequently with generalized disease, but more often with auditory involvement. The latter can develop in utero or postnatally and can be progressive. The major cause of recurrent maternal infection according to restriction enzyme analysis is reactivation of latent virus, which occurs in the face of substantial maternal humoral immunity, even with intrauterine transmission of virus. Reinfection by exogenous virus remains a lesser possibility for maternal recurrences. Even more commonly, CMV can be transmitted at birth from the infected maternal genital tract and postnatally through infected breast milk, especially in highly immune populations. With the possible exception of early pneumonia, these infections appear to be innocuous.

High perinatal seroprevalence of cytomegalovirus in northern Taiwan

AIM

The living style, health-care system and socio-economic environments have changed substantially in Taiwan over past 20 years. This study was aimed to estimate the current perinatal cytomegalovirus (CMV) seroprevalence in northern Taiwan.

METHODS

In a Taiwan Birth Panel Study, 483 pairs of mothers and neonates were prospectively recruited from one tertiary medical center, one local hospital, and two obstetric clinics located in northern Taiwan from April 2004 through January 2005. Sera of their paired maternal and cord blood were tested by an enzyme-linked immunosorbent assay method for CMV IgG and IgM antibodies. Additional data were collected for health measures and epidemiological characteristics through trained interviewers utilising structured questionnaires.

RESULTS

Among 483 mothers studied, 93% were Taiwanese, 6.4% were immigrants from the south-eastern Asia and Mainland China, and 0.6% was aborigines. The seropositive rate of CMV IgG and IgM among the mothers was 91.1% and 3.5%, respectively. The immigrant mothers and the mothers younger than 20 years of age had a higher IgM seroprevalence (P < 0.05). Furthermore, 90.8% of the offspring had CMV IgG seropositivity and yet none of the neonates were CMV IgM positive.

CONCLUSION

The seroprevalence of CMV among childbearing women is high in northern Taiwan. The immigrant mothers and the teenage mothers appear to have higher seropositivity of CMV IgM.

Review and meta-analysis of the epidemiology of congenital cytomegalovirus (CMV) infection

We reviewed studies that reported results of systematic cytomegalovirus (CMV) screening on fetuses and/or live-born infants. The overall birth prevalence of congenital CMV infection was 0.64%, but varied considerably among different study populations. About 11% of live-born infants with congenital CMV infection were symptomatic, but the inter-study differences in definitions of symptomatic cases limit the interpretation of these data. Non-white race, low socioeconomic status (SES), premature birth, and neonatal intensive care unit admittance were risk factors for congenital CMV infection. Birth prevalence increased with maternal CMV seroprevalence. Maternal seroprevalence accounted for 29% of the variance in birth prevalence between study populations. Maternal seroprevalence and birth prevalence were both higher in study populations that were ascertained at birth rather than in the prenatal period. Thus, timing of ascertainment should be considered when interpreting birth prevalence estimates. Birth prevalence was inversely correlated with mean maternal age, but this relationship was not significant when controlling for maternal seroprevalence. The rate of transmission to infants born to mothers who had a primary infection or a recurrent infection during pregnancy was 32% and 1.4%, respectively. Possible maternal primary infections (i.e. seropositive mother with CMV IgM) resulted in congenital infections about 20% of the time, but are likely to represent a mixture of primary and recurrent infections. In summary, CMV is a common congenital infection worldwide that can lead to permanent disabilities. There is an urgent need for interventions that can reduce the substantial burden of this often overlooked disease.

Transmission of cytomegalovirus from mothers to preterm infants by breast milk

OBJECTIVES

To assess the risk of transmission of cytomegalovirus (CMV) by breast milk from CMV-seropositive mothers to their breast-fed preterm infants and to evaluate their outcome.

PATIENTS AND METHODS

The study population comprised breast-fed preterm infants with a birth weight of <1,500 g and gestational age of <35 weeks. Venous blood samples from the mothers and infants were tested for CMV IgG and IgM antibodies on the 5th and 30th day after birth. Breast milk was obtained for CMV DNA detection by polymerase chain reaction and viral culture on the 5th day and on the 3rd, 6th and 12th week. Urine samples of the babies were collected at the same time for CMV culture. Neurodevelopmental assessment was done at 6 months of age, corrected for preterm birth.

RESULTS

Thirty-eight mothers and 42 infants (including 4 sets of twins) were enrolled in the study. A mother-infant pair was excluded because of inadequate breast milk collection. Thirty-six mothers (97.3%) were CMV-seropositive. CMV DNA of breast milk was detected in 35 seropositive mothers. Six infants of 5 mothers were infected (infected group) at a mean of 77 days after birth, and 34 infants of 31 mothers were not (noninfected group). In all the mothers of the infected group, CMV virus could be cultured from the milk whey. The average maternal CMV IgG on day 5 after delivery was higher in the infected than in the noninfected group. Sepsis-like symptoms and hyperbilirubinemia were more frequently noted in the infected infants than in the noninfected, but the difference was not statistically significant. Neurodevelopmental outcome did not significantly differ between the 2 groups.

CONCLUSIONS

The risk of CMV infection in breast-fed premature infants was highest when the mothers shed viable virus in their breast milk. These mothers had high CMV IgG, which may help identify those mother-infant pairs at risk. Inactivation of the virus in milk by freezing may be a way of reducing the transmission of this virus via breast milk.

Cytomegalovirus transmission from breast milk in premature babies: does it matter?

There is evidence that CMV is commonly present in breast milk and is often transmitted to babies. CMV infection acquired postnatally can cause serious disease in very premature babies. Interventions to remove CMV from breast milk are possible but may damage other important constituents.

Congenital cytomegalovirus infection: review of the epidemiology and outcome

Cytomegalovirus (CMV) is one of the most common viral causes of congenital infection. A future decision to lower its incidence by vaccination will depend on epidemiological conditions within a country and on the safety of the vaccine to be used, because a life vaccine may cause latency and subsequent reactivation that still may harm the fetus. The aim was to review the epidemiological studies published so far, with respect to factors that affect the incidence of congenital CMV infection, and factors that may influence its outcome, such as preexisting maternal immunity. The study included the data of 19 studies that were retrieved from a MEDLINE search during the period 1977 to 1997. The incidence of congenital CMV infection varied between 0.15% and 2.0% and seemed to correlate with the level of preexisting immunity in the population. Although preexisting maternal immunity was reported to strongly reduce transmission, the severity of congenital CMV infection (symptoms at birth and or sequelae later in life) was not significantly greater after virus transmission due to a primary infection of the mother as compared with recurrence or reinfection. The data indicate that preexisting immunity of the mother does not significantly mitigate the outcome of congenital infection. Moreover, life vaccines may bear a serious risk when transmittable to the fetus.

TARGET AUDIENCE

Obstetricians and Gynecologists, Family Physicians.

LEARNING OBJECTIVES

After completion of this article, the reader will be able to describe the natural course of a CMV infection, to list the potential sequelae of a congenital CMV infection, to outline potential strategies to prevent transmission of CMV, and to summarize the diagnostic work up of a patient with a potential CMV infection.

[Perinatal infection due to cytomegaloviruses in a public hospital of the municipality of São Paulo: a prospective study]

In order to demonstrate the occurrence of CMV perinatal infection in a middle socioeconomic class population, the authors conducted a 8-month prospective study in 37 children, not infected congenitally, born in a public hospital of São Paulo city, Prevalence of CMV-IgG antibodies in mothers, detected by immunoenzymatic assay (ELISA), was 92.7%. Survival analysis showed that the risk of acquiring CMV perinatal infection diagnosed by virus isolation in human fibroblasts was 30.9%. When the diagnostic method was detection of IgM class antibodies by indirect immunofluorescence the risk was 8.1% (p < 0.05). Milk samples inoculated in human fibroblasts failed to demonstrate the presence of virus. The infected children did not present any signal of disease in a 4-month follow-up.

Early acquisition of cytomegalovirus infection

Two hundred and fifty three infants were screened for cytomegalovirus (CMV) in the urine at birth and were followed up at regular intervals for one year. Twelve per cent (of 249) were excreting virus at 3 months, and 20% (of 234) at 12 months. In all cases infection was subclinical. The major factors determining risk of acquiring infection were the mother's serological state and whether the infant was breast fed. There was no association with social class, mother's age, or whether the child had been in a special care baby unit or a postnatal ward. By one year 33% (of 123) of infants of seropositive mothers had acquired CMV infection compared with 4% (of 123) born to seronegative mothers. Twenty per cent (17) of seropositive women who breast fed had virus isolated from their breast milk on at least one occasion, and 76% (13) of their infants became infected. In four mother-infant pairs comparison of CMV isolates from the mother's milk and the child's urine was made by restriction endonuclease digestion; in each pair infection had apparently occurred with the same strain of virus. All 13 infected infants followed up for three years were still shedding virus. Infection with CMV is common in infancy, and virus shedding persists for years. Congenital infection cannot be distinguished from acquired infection unless the presence of CMV in the urine is identified within three or four weeks after birth, even when clinical problems suggestive of congenital infection are present.

Acquisition of cytomegalovirus infection from birth to 10 years: a longitudinal serologic study

We performed serial serologic tests for cytomegalovirus (CMV) antibody in 177 children born to low- and middle-income families in Houston from 1975 to 1983. Mean duration of participation in the study was 4.8 years (range 1 to 9.6 years). Most rapid acquisition of antibody occurred during the first and second years of life, 13.6% and 12%, respectively; thereafter, annual acquisition varied from 1.5% to 4.6%, up to 10 years. Overall, 59 (33%) of the group were known to seroconvert by age 10 years. This was a minimal figure because of loss to follow-up. Analysis by the Kaplan-Meier method indicated that the probability of remaining seronegative was 65% at age 6 years, and 58% at age 8 years. Variables positively related to seroconversion by multivariate analysis were order of birth, seroconversion in a family member, and breast-feeding. During the first year of life, acquisition of CMV antibody was related to the seroimmune status of the mother. The variables of socioeconomic status, race, age of the mother, and attendance in a day care center did not appear to be related to seroconversion in these children.

Virus excretion and cell-mediated immunity during cytomegalovirus infection among healthy infants and children

Specific cell-mediated immunity (CMI) and virus isolation were examined longitudinally to clarify the mechanism of the cessation of virus excretion in inapparent cytomegalovirus (CMV) infection among healthy infants and children. We measured leukocyte procoagulant activity (LPCA) responses to CMV antigen and to a purified protein derivative of tuberculin (PPD), with results expressed as a percentage reduction of recalcification (RC) time. Based on the results in seropositive and seronegative adult control subjects, reductions in RC time of more than 10% were considered indicative of a positive LPCA response. The CMV-specific LPCA response was negative in all infants shedding the virus, despite the presence of circulating antibodies, but were converted from negative to positive when the virus excretion ceased. This suggests that cessation of the virus excretion in inapparent CMV infection among healthy infants and children probably results from the specific CMI.

Cytomegalovirus in breast milk of Swedish milk donors

81 milk samples collected from 35 donors 3 days to 7 months after delivery were examined for the occurrence of cytomegalovirus (CMV). 30/35 (89%) of the women were seropositive to CMV. The virus was only found in samples from seropositive women collected greater than 8 days to less than 3 months after partus. During this period milk from 23 seropositive donors were tested; 16/23 (70%) excreted CMV. CMV is evidently a very common finding in the milk of seropositive mothers.

Infantile spasms: modern practical aspects

Data on incidence, aetiology, therapy and prognosis of infantile spasms are reviewed. In a large proportion of cases the aetiological factors of infantile spasms can now be established with some certainty. Especially the new neuroradiological and virological investigative methods have enabled a more accurate diagnosis. There have been changes in the aetiologic pattern over the years. The optimal dosage and duration of ACTH or glucocorticoid therapy have not yet been established. In the Finnish study the large ACTH doses (120-160 IE) generally used in many Nordic countries did not carry a better prognosis than the smaller doses (20-40 IE). Side-effects of ACTH therapy are relatively common. They are more frequent with large doses than with smaller ones. Measures can be taken to prevent or treat part of them. The prognosis and related factors in infantile spasms as well as some recommendations to improve them are reviewed.

A prospective study of congenital cytomegalovirus infection in Japan

A prospective study on congenital cytomegalovirus (CMV) infection was carried out in Sapporo, Japan. Only 77 (6.2%) of 1233 pregnant women were seronegative in the first trimester. In such a highly immune population, 11 (0.5%) of 2070 newborn infants were found to have congenital CMV infection. None of them showed any clinical abnormalities during the period of observation (3-24 months), except for a cyst of septum pellucidum in one case. The incidence of congenital CMV infection in the first pregnancies was 1.1% (9/816) and in subsequent pregnancies 0.2% (2/1254). The difference was statistically significant. Three mothers of infants with congenital CMV infection were already seropositive in the first trimester. 26/30 (86.7%) infants, born to mothers with active CMV infection during pregnancy, had started to excrete CMV with urine before the age of 12 months. In contrast, none of the 4 infants born to seronegative mothers excreted CMV.

Sequelae of maternally derived cytomegalovirus infections in premature infants

Eighteen of 106 (17%) infants of seropositive mothers, with birth weights less than 1500 gm, acquired cytomegalovirus from a maternal source. Neutropenia, lymphocytosis, thrombocytopenia, and hepatosplenomegaly developed in some infants concomitant with the onset of CMV excretion. Infected infants who excreted CMV at less than 7 weeks of age had longer oxygen requirements than infants who did not excrete CMV until they were older. Passively derived maternal antibody to CMV fell more rapidly over the first few months of life in sick premature infants than would be expected in term infants. Among six infected premature infants, five had undetectable antibody titers when CMV excretion began. Loss of passively acquired antibody and early excretion of virus appear to be associated with symptomatic CMV infections in premature infants of seropositive mothers.

Prevalence and importance of congenital cytomegalovirus infection in three different populations

A Chilean population was compared to low-income and middle/upper-class populations in Birmingham, Ala., with regard to prevalence of congenital cytomegalovirus infection as well as the importance of this infection in neonatal deaths. In the highly seroimmune Chilean (98%) and low-income Birmingham (82%) groups, congenital infections occurred more often (1.7% and 1.9%, respectively) than in the less immune (56%) middle/upper-income group in Birmingham (0.6%). In 407 autopsies reviewed in Chile no neonatal deaths were attributed to cytomegalic inclusion disease, whereas in Birmingham cytomegalovirus was the cause of death in nine of 938 (1%) newborn infants. These findings further support the concept that, despite an apparent lack of protection against intrauterine transmission, maternal immunity reduces the risk of severe fetal infection.

Prevalence of antibodies to human cytomegalovirus in urban, kibbutz, and Bedouin children in southern Israel

Prevalence of antibody to human cytomegalovirus (CMV) was determined in a sample of 860 healthy children aged 1-13 years in Beer Sheva, in the Negev region of Israel. Three groups of children were tested: (1) urban Jewish children of low, middle, and high socioeconomic levels; (2) 8 rural communes (kibbutz) in which children live in close contact with each other from the 6th week of life under good hygienic conditions and a high standard of living; (3) Bedouin, seminomadic Arabs living in relatively poor hygienic conditions in the desert. Kibbutz children showed a significantly higher rate of CMV seropositivity by the second year of life than urban Jewish and Bedouin children (76% versus 44% and 54% respectively) with a gradual increase to 94% in the 10-13-year age group. Among children living in urban populations a significantly higher prevalence of CMV seropositivity was associated with crowding, but not with other socioeconomic indicators (place of residence, country of origin, or education level of parents). A marked rise of CMV seropositivity with age was found in urban Jewish children in the 2-5-year age group during which time they attend nurseries (44% to 67%) and in the Bedouin children in the 6-9-year age group (59% to 86%) when they first attend school. The data suggest that close contact is of major importance in CMV infection in childhood. The clinical implications of early acquisition and high prevalence of CMV antibodies in the kibbutz setting are discussed.

Molecular epidemiology of cytomegalovirus infections in women and their infants

We studied cytomegaloviruses (CMV's) isolated from mothers and their children to determine whether recurrent infections and transmission to the fetus in immune women are due to reinfection or reactivaton of endogenous virus. Twenty-one strains of CMV from six mother-baby pairs, from two congenitally infected siblings, and from repeat isolates from four women were examined for genetic relatedness, by means of restriction endonuclease analysis of purified viral DNA. Although CMV's from unrelated persons were always different, strains from five to six congenitally infected babies were identical or very closely related to those from their mothers. Strains from congenitally infected siblings were also concordant, as were repeat isolates form three of four women. Major differences in viral DNA were detected in strains recovered from the same woman or from a mother-baby pair in only two cases. Endogenous CMV appears to be most frequent source of recurrent infection and intrauterine transmission in immune women; reinfection also occurs, but less commonly.

Immunohistochemical study of intestinal biopsies from children with atopic eczema due to food allergy

In 18 patients with skin reactions after food challenge and in controls the numbers of immunoglobulin-containing cells in the intestinal mucosa were studied by the direct immunoperoxidase technique; IgE and C3 were studied by FITC-conjugated sera also. Serum immunoglobulins, complement fractions 3 and 4, and reaginic antibodies to the foods were measured during the provocation. None of the patients had any deficiency in the numbers of immunoglobulin-containing cells in the intestinal mucosa or in the serum immunoglobulin concentrations. The numbers of IgM- and IgA-containing cells were higher in the patients than in the controls. But patients and controls had equally low numbers of IgE-containing cells. No deposits of C3 were seen in any of the biopsy specimens. Serum IgE was increased in 13 cases. The presence of reaginic antibodies to cow's milk and cereals correlated well with the clinical reaction (12/15 and 5/7 of the cases). There was a negative correlation between the logarithm of serum IgE and the number of IgA-containing cells in the jejunal mucosa (P less than 0.01). High prechallenge counts of blood eosinophils were seen in seven cases and these showed a close correlation with the eosinophils in the jejunal mucosa (P less than 0.001).

Seroepidemiology of cytomegalovirus infections during the first years of life in urban communities

Using indirect haemagglutination assay, combined with a collection of blood samples on blotting cards, seroepidemiological surveys of cytomegalovirus infections during early infancy have been done in different populations (French and immigrant) in urban areas. The comparison of CMV antibody status of mothers and their children at 10 months and at 2 years of age enables possible factors of viral transmission to be defined. During the first year of life, seropositive mothers were the only source of infection and they remained the main source during the second year. Socioeconomic class and educational level are determinant factors in the incidence of viral transmission.

Development of children with early cytomegalovirus infection

To find out whether cytomegalovirus (CMV) infection during the first months of life influences child development, developmental assessment at the age of 2 years was performed on 116 Finnish children chosen at random in a maternity hospital and followed from birth for the occurrence of CMV infection. Two of the children had congenital infection and 39 were infected after birth but before the age of 6 months. Another five children were infected between the ages of 6 and 12 months, and 70 remained non-infected. The developmental assessment, based principally on the Denver Development Screening Test (DDST), included 7 items for gross motor skills, 6 items for fine motor skills, and 4 items for language development. Significantly more perinatally infected children (7/39) were delayed in speech, compared with the non-infected children (3/70). Furthermore, some items assessing fine motor development were passed better by the non-infected than the perinatally infected children, but the difference in total score was not significant. The performance of the two children with congenital CMV infection did not differ from that of the non-infected children.

Illnesses during the first two years of life and their association with perinatal cytomegalovirus infection

In order to find out whether perinatal cytomegalovirus (CMV) infection causes clinical symptoms or signs or influences the general morbidity of a child, a prospective study was performed on 147 children during their first year of life. 48 infants were infected with CMV perinatally. Reports of clinical infections during the second year were available from a total of 108 infants, and serum samples for viral antibody screening at the age 24 months from 111. No specific symptoms or signs could be attributed to perinatal CMV infection. None of the symptoms previously described in connection with CMV infection in childhood were observed. Urinary tract infections were, however, noticed in the group of perinatally infected children. Judging from the prevalence of illnesses and the frequency of elevated antibody titres against different agents, perinatal CMV infection does not seem to influence the general morbidity of a child. In general, the frequency and distribution of illnesses were the same as previously reported by Finnish authors. Breast-feeding did not protect against infection. The children of CMV seronegative mothers were not resistant to other infections, although all of them escaped perinatal CMV infection.

Epidemiology of cytomegalovirus infections during pregnancy and infancy. A prospective study

The occurrence and possible consequences of cytomegalovirus (CMV) infections were studied in 200 mothers and their children by means of immunofluorescent antibody assays in serum, virus isolation from urine and regular clinical and neurological examinations. The prospective study covered the time from early pregnancy to 1 year post partum. The frequency of intrauterine infections was 2%, while 30% of the children became perinatally infected as indicated by the onset of virus excretion and an antibody response at the age of 2--4 months. Later on the occurrence of CMV infections declined sharply. 23 mothers had no CMV antibodies and none of their children contracted CMV during the first year of life. Maternal antibodies seemed unable to protect the child from CMV infections or to delay the onset of virus excretion in perinatally infected children. Intrauterine infections did not correlate with significant increases in the antibodiy titres of the mothers or the presence of IgM antibodies either in the mother's sera or in the cord sera. Perinatal infections were often associated with the presence of IgM antibodies both in the child and in the mother and in these mothers significant increases in CMV antibody titres were frequently seen, probably indicating an activated latent infection. Immunofluorescent antibody assay correlated well with virus isolations and was more sensitive than complement-fixing antibody assay.

Congenital and acquired cytomegalovirus infections. Virological and clinical studies on a Swedish infant population

The study included two clinical materials. First, the frequency of cytomegalovirus and its clinical significance were studied among 661 Swedish children under one year of age admitted to a paediatric hospital. Before the age of one week 4/326 (1%) children excreted virus. At one month the frequency had risen to 6/52 (12%) and after this age the frequency was constant around 20--25%. Sixty per cent of infants born to immigrants were infected after one month of age. One of the four congenitally infected children had symptoms at birth followed by neurological sequelae. The majority of the infections acquired at birth or in early infancy seemed to be subclinical and without sequelae. Second, a retrospective investigation of 18 695 children born during a six-year period was performed. Two cases of virologically confirmed congenital cytomegalic inclusion disease was found. Regarding seven microcephalic patients in the retrospective study congenital CMV-infection could be excluded in four cases. In the remaining three cases the data did not permit any conclusions regarding the etiology.