Day care as microbiological experiment

Care of children in institutions in which sizeable numbers are grouped by age and held in relatively close contact for 8-12 hours per day could be viewed as an experiment designed to allow testing of hypotheses regarding transmission of infectious agents. Not surprisingly, increased rates of infection and disease due to a number of agents have been associated with day care; these include invasive infections due to Hemophilus influenzae b (pre-vaccine era), Streptococcus pneumoniae and Neisseria meningitidis, rotavirus, Salmonella, Shigella, Giardia

Table 6.4 Features of day-care center based care of preschool children that promote spread of infections

Child/developmental features

Environmental/social factors

Naive to many infections - no immunity from past infection Age/developmental susceptibility to certain infections

Lack of control of body fluids/excreta Unable to manage hygiene independently -handwashing, oral and nasal secretions, toileting, feeding

Oral behavior - everything goes in the mouth


Often inadequate facilities for sanitation Grouping children by age Cohort effect - new susceptibles enter center

Family linkage

lamblia, E. coli, respiratory viruses, varicella, hepatitis A, and parvovirus B 19. In addition to infections that can be attributed to a specific agent, there is evidence that children in day-care settings experience more frequent diarrhea, otitis media, and respiratory tract infections than children kept at home (Churchill and Pickering, 1997).

There are a number of features of day care that favor occurrence and transmission of infections (Table 6.4); these features are attributable to the developmental characteristics of young children and to the peculiar social features of these institutions. Pre-school age children have not yet encountered many common causes of infection, and they lack the adaptive immune responses that result from prior infection. When infected with an agent for the first time, they are more likely to have an illness and more likely to infect others in contact with them than an immune host would be. Hands are a key step in the transmission of many infectious agents, and the importance of hand hygiene and interrupting hand contact with body fluids in preventing spread of infections is well known. Pre-school age children do not have control of body fluids; they often have runny noses or drool, and the majority of those less than three years of age are incontinent of feces and urine. Developmentally, young pre-school aged children are not able to learn and reliably perform the routine procedures of hygiene that reduce contact with body fluids (their own as well as others), or to independently keep their hands clean. They use their mouths to explore their environment, and thus contaminate their surroundings with their oral secretions. Observation of toddlers in day care has shown that they place an object or hand in their mouths as often as 60 times per hour (Hutto et al, 1986).

Features of day care that are peculiar to these institutions include crowding, the cohort effect, and family linkage. Very commonly in day-care centers children are grouped by age, and those of similar age are kept in a single room for most of the day. Even if the room is very spacious (and often it is not), the frequency with which a toddler will have contact with another toddler is dramatically increased compared with a child not in a day-care center. In addition, grouping children by age can result in many (even 20 or more) children of approximately the same age having daily contact with each other - a truly remarkable social change compared with family care. The cohort effect is the result of the fact that each year children reach school age and age out of day care, and a new group of infants or toddlers enters. This new group is likely to be naive with regard to any infections that are endemic in that particular center, as well as to the common community-acquired respiratory and enteric infections that are spread in day-care centers. Thus this age-cohort effect means that there will be a regular supply of new susceptible children in day-care centers. Each child in day care lives with a family, and thus establishes a two-way microbiological relationship between the day-care center and the family. Children can introduce an infectious agent, such as CMV, which they acquired in their family to a day-care center. Children can bring infections home from day care, infecting family members and facilitating further spread of infection in the community; hepatitis A virus infection is the classic example (Hadler and McFarland, 1986).

Ironically, the occurrence of infectious diseases in childcare has created significant public health problems, but investigation of day-care associated infections has improved knowledge of the epidemiology of many infections. Studies of infections in day care have helped establish the following:

• the importance of young children as a source of hepatitis A virus infection

• the ability of intervention with human immune globulin to interrupt a hepatitis A outbreak

• the importance of carriage of pathogenic strains in the occurrence of invasive disease due to Streptococcus pneumoniae and Hemophilus influenzae b

• the impact of varicella vaccine on the occurrence of chickenpox in young children

• the relationship between antibiotic use and carriage of resistant bacteria

• the natural history of primary herpes simplex virus gingivostomatitis and spread of herpes among young children

• the importance of outbreaks of parvovirus B 19 infection in young children as a source of maternal infections

• the importance of young children as a source of maternal CMV infections.

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