Child Care and Common Communicable Illnesses in Children Aged 37 to 54 Months FREE

AS THE NUMBER of women entering the labor force has increased, the number of children cared for outside the home has increased proportionately.¹ Previous research indicates that infants in nonparental care experience more bouts of respiratory tract illness, otitis media, and diarrhea than children reared exclusively at home.^{2 - 17} It is increasingly common for children older than 3 years to attend preschool programs, including children who have never been cared for outside the home as well as those who have been cared for only in informal, small-group settings.¹ Relatively little is known about the illness histories of children who enter large-group care for the first time after age 3 years. Likewise, little is known about whether children who have had experience in large-group care prior to age 3 years may be at reduced risk for illness during the preschool years as a result of previous exposure to pathogens connected with respiratory tract and enteric illnesses.¹⁸

Children who have never been in large-group care prior to age 3 years may be at increased risk of illness as they encounter elevated levels of exposure to pathogens carried by other children in child care settings.¹⁹ By comparison, children with previous experience in large-group care may have developed increased immunity to such pathogens, thus providing some resistance to exposure.²⁰ However, because there are so many serotypes of different viruses connected to the common cold, it is unclear whether exposure prior to age 3 years is sufficient to offset the level of exposure experienced by preschool children in large-group care. Findings from the few studies available are mixed, with some showing higher rates of illness among children newly entering care⁶ and some showing no difference.^{18 ,21} Although the reasons for these differences are not fully clear, they may reflect variation in the methods used to study the relationship between child care attendance and rates of illness (eg, the use of retrospective vs prospective designs, mothers vs child care providers as reporters, and different methods of recruiting participants). Studies also used different sets of control variables in the models tested.⁶

In earlier reports, the National Institute of Child Health and Human Development (NICHD) Study of Early Child Care¹⁷ suggested that children who entered child care during infancy had higher rates of gastrointestinal tract, upper respiratory tract, and ear infections during the first 3 years of life. In this article, we reexamine associations between attendance at child care and the same 3 common infections for children aged 37 to 54 months, a period when many children enter formal preschool programs but before nearly all go to kindergarten. Our data were obtained from approximately 1100 children at 10 different data collection sites across the United States who were participating in the NICHD Study of Early Child Care.

We hypothesized, based on our previous study and results from other studies, that rates of respiratory tract, gastrointestinal tract, and ear infections would be higher for children who had contact with many other children in preschool or child care. The evidence in support of higher rates of respiratory tract illness is reasonably consistent; however, the evidence for higher rates of gastrointestinal tract illness is less persuasive.¹⁹ It is unclear whether children who enter large-group care for the first time after age 3 years show higher rates of respiratory tract illness than children with previous experience in large-group care. This study extends the previous literature by examining these issues in a single prospective investigation involving a diverse sample of children from a variety of locations who were recruited at birth and who have experienced a full array of child care arrangements. The study also addresses the question of whether children acquire some protection against infection as a result of prior experience in large-group care. Because the risk of infection appears to be a more direct function of the number of people to whom one is exposed rather than the type of care received, our study divides child care arrangements by size (>6 vs ≤6) rather than type (eg, center care vs child care homes).^{18 - 20 ,22} Although any cutoff is arbitrary, the number 6 was selected for 2 reasons: (1) many states require that child care arrangements be licensed if more than 6 children are served in a setting, and (2) evidence shows that the risk of infections such as those examined does not rise steeply once the number of children in a setting exceeds 6 to 8.^{11 ,17 ,20}

Families participating in this study were recruited through hospital visits to mothers shortly after the birth of a child during calendar year 1991. Families lived in the areas of Little Rock, Ark; Irvine, Calif; Lawrence, Kan; Boston, Mass; Philadelphia, Pa; Pittsburgh, Pa; Charlottesville, Va; Morganton, NC; Seattle, Wash; and Madison, Wis. Of the 8986 mothers who gave birth during the sampling period, 5416 (60%) met the eligibility criteria. Mothers were required to be healthy, older than 18 years, and conversant in English with a singleton child whose birth was normal and uncomplicated; families had to be living in a reasonably safe neighborhood less than 1 hour from the research site and not planning to move. Of the mothers, 130 (1%) refused to be interviewed and 308 (3%) refused to be contacted again. Of the 5416 eligible families, 3015 (56%) were selected using a conditional random sampling plan that ensured that the recruited families reflected economic, educational, and ethnic diversity. Of the 3015 families selected for participation, 1526 (51%) agreed to participate. The remaining 1489 families could not participate for a variety of reasons: 60 infants remained hospitalized for 7 days postpartum, 91 families planned to move, 512 could not be contacted, 641 refused, and 185 had other reasons (most of these said that they did not have the time). Of the 1526 families who agreed to participate, 1364 (89%) completed the initial data collection visit and gave signed consent when the child was 1 month old.

Comparisons of several key demographic and child variables were made between the 51% of eligible families who agreed to participate and the 49% who did not. There were several small (effect sizes were always <0.25) but statistically significant differences. Mothers who agreed to participate were about a year older on average (mean age, 28.0 vs 27.0 years), a little better educated (65% with more than a high school degree vs 50%), and less likely to be from minority backgrounds (19% vs 24%); however, the participating mothers were no more likely to be married. The children from participating families were typically a little heavier at birth (3490 g vs 3393 g).

We obtained information about parents and children using face-to-face interviews with the mother when the child was 1, 6, 15, 24, 37, and 54 months old and from telephone interviews done when the child was 3, 9, 12, 18, 21, 27, 30, 33, 42, 46, and 50 months old. We obtained information about the family context, the type of child care used, changes in child care arrangements, the number of children in the child care arrangement, the amount of time the child spent in child care, and the child's health status and illnesses. The entire data collection protocol was reviewed by a steering committee supervised by the NICHD and was reviewed annually by the institutional review boards of the 10 participating institutions responsible for data collection.

Four pieces of demographic information about families were used: mother's level of education, family size, presence of the father or another adult partner in the home, and family income (the income-to-needs ratio).²² Child characteristics included ethnicity and sex. Ethnicity was included as a factor in the statistical models to control for reporter bias. Previous studies, including the National Health and Nutrition Examination Survey II, have shown a tendency on the part of African American mothers to underreport common illnesses.^{17 ,23} The early childhood version of the Home Observation for Measurement of the Environment²⁴ (HOME) inventory was administered during home visits when the child was 6, 15, 37, and 54 months old. The HOME assesses the quantity and quality of stimulation and support available to the child in the home environment.

During the face-to-face and telephone interviews, mothers were asked if the child had had at least 1 instance of an ear infection, respiratory tract illness, or gastrointestinal tract illness since the last interview.

Child care information included type of care (center care, child care home, care by a relative, or care in the child's own home by a nonrelative), total number of other children in all of the child's nonmaternal care arrangements during a particular data collection interval, and hours in care (how many hours on average the child spent each week in all forms of child care).

The focus of this study was on illnesses occurring between the ages of 37 and 54 months. To determine whether the prevalence of each illness varied across time and whether the illness varied as a function of background characteristics, family circumstances, and child care experiences, longitudinal logistic regression analyses were conducted using the generalized estimating equation approach.²⁵ Separate intercepts were estimated for each child. This approach adjusts for dependency in the data by using repeated measures. Time-invariant predictors (between-subject variables) included site, mother's level of education, ethnicity, sex, family income-to-needs ratio averaged from the 6- and 54-month assessments, total number of hours in child care from birth to 36 months, whether the child was in care with 6 or more other children (large-group care) during the first year of life (birth to age 12 months), whether the child was in large-group care during the second year of life (13-24 months), and whether the child was in large-group care during the third year of life (25-36 months). Site was used as a predictor to help control for heterogeneity in findings resulting from the use of 10 different locations for data collection. Time-varying predictors included several measures of family, child, or child care experiences that were obtained at each of the 4 assessment points (37-42 months, 43-46 months, 47-50 months, and 51-54 months). These included the child's age, child's age squared, presence of a spouse or other adult partner in the household, household size, average number of hours in all forms of child care during the target assessment interval, interaction between hours in care from birth to 36 months and hours in care during the target assessment period, and whether the child was in a child care arrangement with at least 6 other children during the target assessment period. Season (ie, the proportion of months during an assessment interval that occurred during the winter flu season) was also used as a time-varying predictor. For the 37- to 42-month, 43- to 46-month, and 47- to 50-month assessment periods, the HOME measure was based on the mean HOME score from the 6-, 15-, and 37-month administrations of the HOME inventory (first the scores were standardized, and then the mean was calculated). For the 51- to 54-month assessment period, the HOME measure was based on the mean HOME score from the 6-, 15-, 37-, and 54-month administrations of that instrument.

Table 1 indicates results from the longitudinal logistic regression analyses of each illness for the whole sample. It displays odds ratios with accompanying 95% confidence intervals for each aspect of child care experience examined, controlling for the family background and child characteristics described previously.

As expected, during the winter flu season, children were more likely to have each of the 3 illnesses examined (about 15% more likely to have gastrointestinal tract illness and 33% more likely to have an upper respiratory tract infection). Neither the number of hours spent in child care prior to age 3 years nor the number of hours per week children spent in child care from ages 37 to 54 months bore a relationship to the likelihood of contracting a communicable illness. The only 2 child-related conditions that mattered were whether the child was in a care arrangement with at least 6 other children during the assessment period and whether the child was in large-group care (ie, care with 6 or more other children) between ages 25 and 36 months. Children concurrently in large-group care were 2.2 times as likely to have an upper respiratory tract illness as children reared at home or in small-group care. Likewise, they were about 1.6 times as likely to have an ear infection and approximately 1.4 times as likely to have a gastrointestinal tract illness. Experience in large-group care during the first 2 years of life was not protective against contracting an illness during the period examined in this study (ages 37-54 months). However, children who were in large-group care in the third year of life had about a 34% decrease in the likelihood of contracting an upper respiratory tract illness between ages 37 and 54 months and a 24% decrease in the likelihood of contracting a gastrointestinal tract illness.

Finally, some research on the effects of child care has focused on the number of siblings rather than overall household size. Accordingly, we re-ran all analyses substituting number of siblings for household size. The results were essentially the same. That finding was not surprising in view of the r = 0.88 correlation between household size and number of siblings in this sample.

Findings from the NICHD Study of Early Child Care provide evidence that children's experience in nonmaternal care relates to common childhood infections during the first 3 years of life, especially if the child is enrolled in large-group care.¹⁷ Findings from this extension of the study showed 2 things. First, children who were in group care with 6 or more other children aged 24 to 36 months were less likely to contract a gastrointestinal tract or upper respiratory tract illness between the ages of 37 and 54 months compared with children who entered large-group care for the first time after age 3 years. On the other hand, experience in large-group care during the first 2 years of life had no effect on the likelihood of contracting communicable illnesses during that period. Thus, the findings are inconclusive regarding whether experience in child care during infancy confers only a short-term benefit or whether the results that emerged between ages 37 and 54 months represent the earliest stages of more long-term immunity. Findings from the Tucson Children's Respiratory Study showed that children who entered large-group care in infancy had more colds than home-reared children at age 3 years but had fewer colds than these children by age 6 years.¹⁸

Second, children who were in large-group care between ages 37 and 54 months were generally at increased risk of upper respiratory tract illnesses, gastrointestinal tract illnesses, and ear infections (particularly upper respiratory tract illnesses) compared with children reared at home or those who participated in small-group nonparental care. On average, children in large-group care during the preschool years were about twice as likely to have a respiratory tract illness, approximately 1.5 times as likely to have a reported ear infection, and about 1.4 times as likely to have a gastrointestinal tract illness. In sum, our study partially confirms the findings reported by Hurwitz et al⁶ and partially contradicts those reported by Nafstad et al.²¹

In contrast to reports that the likelihood of acquiring communicable illnesses increases with the amount of time spent in child care,²⁶ we found little evidence that hours of care per week increased illness rates for any of the 3 diseases examined. This finding, which contradicts the results from some earlier studies, may have emerged because most of the children in our study spent more than 25 hours per week in nonmaternal care after age 3 years. In effect, most children were in care longer than the threshold amount of time needed to contract most communicable illnesses.

For preschool-aged children, the likelihood of contracting an upper respiratory tract illness seems to be primarily a function of exposure to a sufficient number of other children. Thus, children who attended child care arrangements with more than 6 children were at notably increased risk. Our findings regarding the relationship between ear infections and number of children in child care are reminiscent of those by Paradise et al.¹¹ They found a "strong positive relationship (for days with middle ear effusion) to the degree of exposure to other children"¹¹ (p323) in arrangements with more than 5 children. Although the evidence that prior experience in child care afforded children protection against respiratory tract illnesses during the preschool years was not unequivocal, continued analysis of the illness rates of these children as they enter school will provide useful information regarding whether early exposure to the pathogens that cause common communicable illnesses leads to a lower risk of illness after school entry. The findings of Ball et al¹⁸ show that experience in large-group care (defined as being with 6 or more unrelated children) prior to age 3 years is associated with a decreased likelihood of having a cold during the early school years. However, it is important not to overemphasize the cutoff point of 6 because all cutoff points are to some extent arbitrary.

Care should be taken in applying the results from this study to children from high-risk and non–English-speaking families. The exclusion criteria used to select families for the study, coupled with slightly higher rates of participation among children from backgrounds of high socioeconomic status, makes it unclear whether findings from this study are generalizable to low-income children. Previous studies have shown that children from families of low socioeconomic status are more likely to receive lower-quality and more sporadic child care—factors that may increase their risk of exposure to communicable illnesses.^{27 - 28}

Corresponding author: Robert H. Bradley, PhD, Center for Applied Studies in Education, University of Arkansas at Little Rock, 2801 S University Ave, Little Rock, AR 72204 (e-mail: rhbradley@ualr.edu).

Reprints: NICHD Early Child Care Research Network, CRMC, NICHD, 6100 Executive Blvd, 4B05, Rockville, MD 20852.

Accepted for publication October 18, 2002.

We express our appreciation to the study coordinators at each site who supervised data collection, the research assistants who collected the data, the care providers who allowed us into their worlds to carry out our observations, and the families who cooperated willingly with our repeated requests for information.

Birkbeck College, University of London, London, England: Jay Belsky, PhD; University of Washington, Seattle: Cathryn Booth, PhD, Susan Spieker, PhD; University of Arkansas at Little Rock: Robert Bradley, PhD; University of North Carolina at Chapel Hill: Margaret Burchinal, PhD, Martha Cox, PhD; University of Pittsburgh, Pittsburgh, Pa: Susan Campbell, PhD; University of California–Irvine: Allison Clarke-Stewart, PhD; NICHD, Rockville, Md: Sarah L. Friedman, PhD; Temple University, Philadelphia, Pa: Kathryn Hirsh-Pasek, PhD, Marsha Weinraub, PhD; University of Texas at Austin: Aletha Huston, PhD; St Joseph's University, Philadelphia, Pa: Elizabeth Jaeger, PhD; Research Triangle Institute, Research Triangle Park, NC: Bonnie Knoke, MS, Lori McLeod, PhD; Wellesley College, Wellesley, Mass: Nancy Marshall, EdD, Wendy Robeson, EdD; Harvard University, Boston, Mass: Kathleen McCartney, PhD; University of California at San Diego: Philip Nader, MD; University of North Carolina at Greensboro: Marion O'Brien, PhD; University of Texas at Dallas: Margaret Tresh Owen, PhD; University of Virginia, Charlottesville: Robert Pianta, PhD; Georgetown University, Washington, DC: Deborah Phillips, PhD; University of Wisconsin–Madison: Deborah Lowe Vandell, PhD.

Previous research indicates that infants in nonparental care experience more bouts of respiratory tract illness, otitis media, and diarrhea than children reared exclusively at home. By age 3 years, the rates of common communicable illnesses experienced by children in child care are only slightly higher than those experienced by home-reared children. However, very little is known about the illness histories of children who enter large-group care after age 3 years and whether children with prior child care experience are at reduced risk for illness during the preschool years as a result of their previous exposure to the pathogens connected to respiratory tract and enteric illness.

A 10-site longitudinal study of more than 1100 children who had received follow-up since birth indicates that children who were in large-group care between ages 2 and 3 years were less likely to contract gastrointestinal tract and respiratory tract illnesses between ages 3 and 4½ years than children who entered large-group care for the first time after age 3 years. However, children in large-group care between ages 3 and 4½ years were at increased risk for communicable illnesses compared with home-reared children and those in small-group nonparental care.