HCMV seroepidemiology is determined by factors such as age and socio-economic/public health conditions, and varies from 40% to 100% seropositive adults in different geographic and socio-economic populations. According to the epidemiological data obtained in 2009, the HCMV seroprevalence in Ji'nan, China, is 33.49% in people <20 years old while it is 48.3% in those >20 years old
. Our seroepidemiological survey showed that the overall infection rate of HCMV in children from 2009 to 2012 was 42.5%, higher than that in Ji'nan. Compared to other countries, the rate was lower than in African populations <10 years old, but higher than populations in developed countries <15 years old. In our data, the HCMV-IgG-positive rate was 34.2%, suggesting serological evidence of past infection; this is a lower positivity-rate than in developed countries. However, in infants <6 months old, it is unclear whether this was due to vertical transmission or fetal transmission from the mother.
A clinical study of HCMV reporting 186 hospital cases from 2003 to 2007 showed that the onset age of HCMV infection is usually within the first year
, more in males than in females (1.9:1). From our survey, new HCMV infections were concentrated in infants <6 months old, which is consistent with previous reports.
Our data showed that the total infection rate was significantly different between age groups (except for 15–28 days) and 6 months seemed to be the threshold. Ages under 6 months patients due to the impact of mother transmitted IgG antibody and gradually increased recent infection rate, the cumulative infection rate was the highest until 6 months. Nevertheless, after 6 months a decreased trend was seen. The reason might be that the IgG titers decrease gradually with increasing age.
In addition, the statistical analysis showed that both the overall distribution and active HCMV infection did not different by gender in children in Weifang (p >0.05). It is known that HCMV can be transmitted to the newborn via the birth canal, breast milk or other sources. In preterm infants, who are easily infected by HCMV, the acquired infection ranges from 12–22%, depending on the gestational age and the breastfeeding duration and frequency as well as other factors
. Thus, although breast milk is recognized to be the ideal feeding method for newborns, it can transmit HCMV to the offspring of HCMV-seropositive mothers. A seroepidemiologic study in Taiwan indicated that the duration of breastfeeding is a significant risk factor for HCMV seropositivity. Children given HCMV-seropositive breast milk for >24 months are 2.43 times more likely to be infected than those who are breast fed for ≤24 months (p = 0.0001)
. Heating and freezing procedures can prevent infection via breast milk in preterm infants
[10, 11]. While these procedures might not completely eliminate HCMV, they are less harmful to the immunological factors contained in breast milk
Seroepidemiological studies also showed that in developed countries, the HCMV antibody-positive rates in the high-level socio-economic population is 40-60% while in the low-level population the rate is >80%
. According to one analysis, the HCMV infection ratios in low-, medium- and high-income families are 3.5:2.1:1.5
. In our survey, 57.9% of the HCMV-IgM-positive hospitalized children were from rural areas and 42.1% from urban areas, suggesting economic conditions can greatly affect HCMV infection.
It should be noted that the screening of patients for HCMV infection is generally performed using either competitive or indirect ELISAs which detect both IgG and IgM antibodies. A major disadvantage of HCMV IgG/IgM antibody detection is the relatively high frequency of false-positives which may be observed in the absence of specific IgG antibody
. False-positive reactions occur in various conditions unrelated to active HCMV infection, including polyclonal antibody production during infections with other herpes viruses
, Epstein-Barr virus, and autoimmune disease
[18–20]. In this study, we excluded other possible infections. Limitations of this survey are that all patients needed to be screened for the presence of CMV-DNA, especially late gene transcripts in their blood or urine samples by using nested-PCR
. Despite its preliminary character, this study clearly indicates that recent HCMV infection is centered on the first 6 months of life with the evidence from a large population sample; and the details of breast milk from HCMV IgM-positive mothers as a source of infection in children <6 years old remain to be clarified.