Congenital CMV is a silent global burden that remains largely unrecognized in infants due to the high prevalence of non-specific symptoms or asymptomatic patients [20]. It has been widely demonstrated that women have poor knowledge of cCMV infection compared to other less frequent congenital diseases, such as Down syndrome, toxoplasmosis, and human immunodeficiency virus (HIV) infection [21,22,23]. Given the poor awareness and knowledge of cCMV infection among the world’s population and the lack of targeted prevention strategies, cCMV can be considered “an elephant in our living room” [24]. Providing proper prenatal education aimed at increasing awareness and knowledge of cCMV infection among pregnant women is a need highlighted by studies conducted in several countries, including the United States [25], Canada [26], Japan [22], Australia [27], Saudi Arabia [23], Germany [28], France [29], Switzerland [21], Italy [30], Spain [31], Portugal [32], the United Kingdom [33], and the Republic of Ireland [34]. Moreover, it is crucial to increase awareness of cCMV infection also among the male population and healthcare providers. In particular, men can serve as a vector for maternal infection and should be educated about behaviors that reduce the risk of CMV transmission, such as using condoms during sexual intercourse [30]. Similarly, healthcare professionals should play a key role in raising awareness among pregnant women through the dissemination of appropriate information [35]. However, their knowledge about cCMV is often low, negatively impacting prenatal counseling [31,36]. Indeed, most women are unaware of cCMV or how to reduce the risk of infection during pregnancy, in part due to poor health professionals’ awareness [37]. In this context, it is necessary to promote health campaigns and health education strategies to enhance awareness about cCMV infection [31]. All pregnant women should be adequately advised to avoid certain behavioral practices that increase the risk of CMV infection, such as kissing a child on the lips, sharing utensils, changing diapers, and practicing unsafe sex [10]. As a matter of fact, because no vaccine is currently available and treatment options are limited, the main measures to prevent CMV infection during pregnancy are based on rigorous respect of the hygienic-behavioral rules, such as handwashing after exposure to young children’s body fluids [10,30].

Diagnosis of primary CMV infection during pregnancy can be made by detection of CMV IgG seroconversion or CMV IgM positivity associated with low IgG avidity [38]. Currently, most public health policies and international scientific societies do not routinely recommend universal maternal prenatal screening for CMV infection due to the following reasons [30,39,40,41]: (a) lack of highly sensitive and specific prenatal tests; (b) CMV serological screening is not applicable to non-primary CMV infection; (c) lack of effective interventions to prevent transmission to the fetus; (d) lack of safe and effective prenatal treatments; (e) inability of laboratory tests to predict which babies will develop long-term neurological and audiological complications; (f) potentially increased rate of unnecessary abortions. Moreover, the false-positive rate would be much higher in the screened population than in women preselected for suspected CMV infection and, as a result, many pregnant women would undergo unnecessary additional testing and invasive procedures [39,42]. Therefore, according to the general agreement, CMV serologic testing should be offered only to pregnant women with symptoms and/or signs suggestive of primary CMV infection (e.g., influenza-like illness and/or fetal abnormalities on prenatal ultrasound examination) [42]. However, most pregnant women want to have CMV serological screening once informed about cCMV infection [43]; some of them make use of the maternal serological screening even if it is not recommended by the national guidelines [28,30,38,44,45]. As a matter of fact, maternal CMV screening followed by targeted neonatal CMV screening (testing neonates whose mothers become seropositive during pregnancy) may help identify asymptomatic cCMV cases in an early stage; Naessens et al. reported that this type of screening allowed the detection of 82% of all cCMV infections [46]. Moreover, women who are aware that they are susceptible to primary CMV infection based on serology are more likely to practice hygiene measures [45]. It is also important to highlight that maternal administration of oral valaciclovir following maternal primary infection in the first trimester of pregnancy has been demonstrated to be effective in reducing the rate of fetal CMV infection [47]. Therefore, maternal CMV screening followed by valaciclovir prevention may prevent most severe cases of cCMV infection [40]. However, possible adverse effects, especially acute renal failure, should be taken into consideration in pregnant women taking valaciclovir. Further studies are needed to investigate the safety and effectiveness of prenatal valaciclovir therapy in pregnancies with maternal CMV infection [48].

Diagnosis of cCMV infection can be performed by detection of CMV DNA in urine or saliva samples within 2–3 weeks after birth, or later by polymerase chain reaction (PCR) assay of dried blood spot (DBS) samples on the Guthrie card, which are universally collected within 3 days from birth [49,50,51]. Targeted cCMV screening through saliva PCR in children who fail the universal newborn hearing screening (UNHS) has been demonstrated to fall within the range between cost-neutral and cost-saving [52]. As a matter of fact, this cCMV screening method is feasible and acceptable to parents, providing the opportunity to start the treatment with oral valganciclovir within the first month of life [52,53]. However, performing cCMV neonatal screening only in babies who fail UNHS would not identify asymptomatic CMV-infected children who will develop late-onset HL [54]. A large study by Fowler et al. has shown that 43% of infants with CMV-related SNHL in the neonatal period and cCMV infants who are at risk of late-onset SNHL were not identified by UNHS [55]. Therefore, new strategies to identify all children with cCMV who remain at risk of late-onset and progressive HL are of paramount importance. In this context, it may be beneficial to extend targeted cCMV screening to children who pass UNHS but are at increased risk of cCMV infection, such as those born SGA or with microencephaly [54]. Indeed, an expanded targeted early cCMV testing program has been shown to improve detection rates of symptomatic cCMV cases, and should be considered as a valid alternative approach to hearing-targeted CMV testing [56]. In particular, cCMV infection should be suspected in all newborns: (a) whose mothers became CMV-seropositive during pregnancy; (b) who have received a confirmed diagnosis of SNHL; (c) who have signs and symptoms suggestive of CMV infection (e.g., SGA, microcephaly, petechiae, thrombocytopenia, unexplained hepatosplenomegaly, idiopathic elevated liver enzymes, and jaundice); (d) who have abnormal neuroimaging consistent with CMV infection (e.g., periventricular calcifications, ventriculomegaly, subependymal pseudocysts, white matter changes, cerebral or cerebellar hypoplasia, and lenticulostriate vasculopathy) [14,57].

According to the general agreement, treatment with antiviral drugs should be considered only for neonates with severely/moderately symptomatic cCMV infection at birth [14,61]. Intravenous ganciclovir and its orally available prodrug, valganciclovir, are the first-line antiviral agents of choice [62]. Newborns with non-life-threatening disease are generally treated with oral valganciclovir; the recommended dose is 16 mg/kg/dose, administered twice daily for a total of 6 months [63]. Antiviral therapy should be started as soon as a virologic positive result is available, being effective in improving hearing and neurodevelopmental outcomes if started within the first month of life [62]. However, some studies have demonstrated the benefits and safety aspects of treating children with cCMV even beyond the recommended neonatal period [64,65]. Oral valganciclovir appears to have a beneficial role in both preventing and improving SNHL in children with symptomatic cCMV infection [66,67]. Although prolonged valganciclovir treatment for cCMV is generally safe and well-tolerated, a close monitoring of the white blood cell count and hemoglobin levels is mandatory; in particular, severe neutropenia (absolute neutrophil < 500/μL) is a possible adverse effect that can lead to treatment discontinuation [68]. Some retrospective studies have suggested that even children with isolated SNHL due to cCMV may benefit from valganciclovir [30,69,70], but to date no specific clinical trial data are available to support the routine use of antiviral treatment in these patients [71]. However, a study conducted in the United States has shown that the proportion of infants with cCMV treated with valganciclovir has increased markedly in recent years for all disease severity groups, including those without clinical findings [72]. It is crucial to point out that the use of valganciclovir may be associated with many serious adverse effects, such as neutropenia, anemia, thrombocytopenia, hepatotoxicity, and nephrotoxicity [63,68]. Thus, although many experts encourage the use of valganciclovir in infants with isolated HL [14], shared decision-making between pediatricians and parents is extremely important due to the sparse data on benefits and the known risks of treatment [71].

A vaccine against cCMV infection is a major public health priority. Although the development of CMV vaccines began in the 1970s [75,76], no CMV vaccine is available for humans so far [77]. In the year 2000, the National Academy of Medicine of the United States published a document that assigned the human CMV vaccine a high development priority [78]. As a matter of fact, the development of a vaccine capable of conferring effective protection against primary CMV infection may be a valid solution to reduce the serious consequences of intrauterine CMV infection. However, it should be emphasized that a strategy aimed at preventing only primary maternal infection would not address HL and other severe neurological sequelae secondary to cCMV in children born to mothers with pre-existing CMV immunity [79]. Indeed, maternal non-primary CMV infection during pregnancy is considered the greatest burden due to the high seroprevalence of CMV among women of childbearing age [9,30]. Therefore, ideal vaccines should have the ability not only to protect seronegative women from primary infection but also to enhance the immune response in seropositive women to prevent reactivation or reinfection [80]. A viable solution might be a recombinant CMV glycoprotein B vaccine with MF59 adjuvant that appeared to boost both antibody and CD4 T-cell responses in previously CMV-seropositive women, thus raising the possibility to prevent vertical transmission [81]. Unfortunately, CMV vaccines evaluated in clinical trials so far have demonstrated only about 45–50% efficacy against CMV primary infection and none of these have been approved [82,83]. However, a recent mathematical model by Byrne et al. has predicted that even modestly protective CMV vaccination of young children would significantly reduce both CMV transmission to pregnant women and the prevalence of cCMV [84].

The association between cCMV infection and HL was first described in 1964 [87]. Although many studies have been conducted on this important public health issue since then, cCMV infection remains the leading non-genetic cause of SNHL in children in the developed world [16,17,62,88]. Congenital CMV is estimated to be responsible for HL in one in five hearing-impaired children with no other known risk factors [89]. A possible pathogenetic hypothesis is that CMV infection of the marginal cell layer of the stria vascularis may alter potassium and ion circulation, dissipating the endocochlear potential with consequent degeneration of the hair cells of the organ of Corti [90]. Paradoxically, hair cells appear to be spared by CMV infection [89].

The characteristic of HL due to cCMV infection are extremely variable [16,17,88]. First, HL is typically sensorineural and can occur in both symptomatic and asymptomatic children [16,17,88]. Although HL in asymptomatic children (“isolated HL”) is often considered a distinct category, some European experts classify infants with isolated SNHL as having severely symptomatic cCMV [14,71]. SNHL can be present at birth (“congenital HL”) or appear sometime later in life (“delayed-onset HL”) [16,17,88]. A recent systematic review by Vos et al. has reported that the prevalence of HL at birth is over 33% among symptomatic CMV-infected newborns and less than 15% in asymptomatic infections [88]. SNHL presents with later onset in about 10–20% of cCMV cases [57]. The hearing threshold may fluctuate or deteriorate over time [16,17,88]. Fluctuating HL is typically not explained by concurrent middle ear infections and may occur at only a few frequencies [16]. Hearing threshold deterioration can be observed in about half of children with SNHL at birth, regardless of whether they have asymptomatic or symptomatic infection [16]. However, in children with symptomatic CMV infection, HL is generally more severe and tends to progress earlier [16,57]. It is important to underline that a diagnosis of cCMV does not exclude the coexistence of other disorders that might explain hearing deterioration, such as genetic syndromes, specific mutations in genes associated with isolated HL, or ear malformations [30]. According to Peterson et al., the sub-cohort of CMV-positive newborns with symmetric mild-to-moderate bilateral HL will have at least a 7% chance of having pathogenic gene variants associated with HL [91]. Therefore, children with bilateral symmetric SNHL should undergo comprehensive genetic testing, regardless of cCMV status [91].