Cytomegalovirus as an occupational risk in daycare educators.

Cytomegalovirus (CMV), a member of the herpesvirus group, is a double-stranded DNA virus (1,2). As with other herpesvirus, such as herpes simplex, varicella-zoster and Epstein-Barr, recurrence of infection can occur throughout the lifespan, leading to re-emergence of viral shedding (2,3). After infection, CMV disseminates to various organs of the body and can be found in bodily fluids such as blood, tears, feces, cervical secretions, semen and breast milk (4). However, CMV excretion occurs mainly in urine and saliva (5). The exact mode of transmission is not well understood, but both vertical (mother to infant) and horizontal (person to person) transmission are common. It is generally accepted that horizontal transmission of CMV requires intimate contact with secretions and that mucosal contact with infectious secretions or tissue may be required (4,6). However, this is based on epidemiological evidence and has not been proven experimentally (4). Vertical transmission can occur prenatally or perinatally from an infected mother to her child (6). Infection in healthy adults and children is usually asymptomatic (4). However, symptomatic infection characterized by a mononucleosis-like illness with fever, malaise and lymphadenopathy can develop (5). In immunocompromised individuals with impaired cell-mediated immunity, CMV can lead to more severe sequelae and is one of the most common opportunistic pathogens (4). However, the major public health concern for CMV focuses on congenital infection. During maternal infection in pregnancy at any gestational age, CMV can cross the placenta, leading to in utero transmission of the virus to the fetus (4). Whereas pathology can occur in the lungs, liver, spleen, heart and brain, the most severe damage occurs in the developing nervous system, with possible outcomes including seizures, mental disabilities, deafness and blindness (5). The risk of delivering an infant with symptomatic CMV infection after in utero exposure to the virus is between 10% and 20% (7). An additional 10% to 15% of fetuses exposed to CMV in utero will be asymptomatic at birth, but will develop hearing loss and other adverse neurological sequelae later in life (5). Congenital CMV occurs in 0.3% to 1.0% of all live births worldwide and is the most common congenital infection (2,8,9). CMV disease can result from primary or recurrent infection. Recurrent infection can occur in one of two ways: reactivation of latent virus, or reinfection from a new strain of CMV (1). Pre-existing maternal antibodies in response to CMV have long been considered protective against congenital infection in the offspring, both in terms of likelihood of in utero transmission (10) and of severity of adverse effects (11,12). However, it has been suggested that the relationship between recurrent infection and congenital CMV has been underestimated due to diagnostic limitations (13). Recent studies have shown the occurrence of congenital CMV in women with recurrent infection (14–18), occasionally with similar health outcomes in both primary and recurrent infection (7). However, it is generally understood that the risk of congenital CMV infection is greater in the offspring of women with a primary infection. CMV infection occurs worldwide, although patterns of infection and transmission can vary regionally and among different patient populations. In industrialized countries, CMV rates are high in young children, with disease acquisition occurring in utero, during childbirth through exposure to genital secretions, in infancy through breastfeeding from seropositive mothers, or in childhood through contact with infected children (19). The development of antibodies from exposure to CMV increases steadily after childhood, and then plateaus in adulthood, where seroprevalence is approximately 40% in industrialized countries (8,19,20). Children are thought to be a common source of CMV for women of childbearing age (5,21,22). In addition, sexual transmission of CMV occurs among adults and adolescents (8,23). However, the epidemiology of CMV appears to be changing due to an increased use of daycare centres, which has increased the transmission of CMV among children and adult contacts (24). This is of concern for daycare educators who work in these settings and are in frequent contact with young children. Because a higher rate of female employment has resulted in greater demand for outside-of-home care (25), increasing attention is being directed to infectious disease transmission in the daycare centre.