Daycare attendance is associated with increased incidence of respiratory infections at preschool age and it has been suggested that the incidence simply shifts to earlier ages such that the overall incidence remains similar. However, respiratory infections early in life might lead to a higher use of healthcare resources.

Upper respiratory tract infections (URTIs) and acute otitis media (AOM) are the most common reasons for doctor consultations and antibiotic use in children. The primary care incidence of URTI, including AOM, in children up to four years of age is estimated at approximately 400 per 1,000 child-years [1, 2]. These infections have a significant impact on the child and on family life and carry a considerable economic burden [3–7].

Daycare attendance is a well-established risk factor for URTIs and AOM in preschool children [8–13]. Early life daycare attendance, however, has been suggested to protect against the common cold and ear infections beyond the preschool years [14–16]. Although this implies that daycare attendance influences the timing of infections rather than the overall number of infections a child experiences during childhood, the risk of infection-related complications might be higher during infancy compared to childhood, due to immaturity of the immune system [17].

Previous studies showed higher general practitioner (GP) consultation and antibiotic prescription rates in daycare attendees [12, 18–22]. Furthermore, daycare attendance leads to higher specialist referral rates in children under the age of two years [23]. Whether this increased use of healthcare resources among daycare attendees at preschool age is offset by a lower use of healthcare resources beyond preschool age in the same children remains to be determined.

The aim of this cohort study, therefore, is to assess the long-term effect of first-year daycare attendance on the number and timing of GP diagnosed URTI and AOM episodes and total use of healthcare resources up to six years of age.

This study showed that the use of health care resources up to the age of six years was higher in children who entered day care in the first year of life compared to children cared for at home during that period, in spite of a similar total number of GP-diagnosed URTI and AOM episodes. This effect was most pronounced in children entering daycare between six to twelve months of age when compared to children starting at an even earlier age.

There is little doubt that daycare attendance is associated with an increased incidence of respiratory infections at preschool age (<4 years of age) [9–12, 21, 28]. The daycare environment provides a setting that facilitates transmission of infectious diseases. Prospective studies investigating the association between daycare attendance and infections beyond preschool age, showed a protective effect of daycare against respiratory infections in later childhood [14–16]. Our study confirms these findings to some extent, that is, children attending daycare before six months of age have lower rates of URTI and AOM after the age of four years and the cumulative incidence of URTI and AOM in the first six years was not significantly different in children who did and did not attend daycare in their first year of life. This suggests that first-year daycare attendance influences the timing of infections rather than the overall number of infections a child experiences during childhood. Notably, our study showed that the impact of URTI and AOM episodes on the child’s health in the first six years of life was substantially higher in children attending daycare as demonstrated by the increased number of GP consultations, antibiotic prescriptions and referrals among these children. These associations have, until now, only been demonstrated in preschool aged children [18–20, 22, 23]. Our study has demonstrated that the increased use of healthcare resources for URTI and AOM in children attending daycare during early infancy is persistent and not fully compensated by a lower use of healthcare resources during school age.

The increased use of healthcare resources in first-year daycare attendees suggests that early URTI and AOM episodes are more severe compared to later infections. Interestingly, children who enter daycare between six and twelve months of age show consistently higher healthcare resource use when compared to children entering before six months of age. A possible explanation may be the fact that children who attend daycare early in life have higher levels of maternal antibodies when being first exposed to pathogens compared to children attending daycare from six months of age [29, 30]. Another explanation could be that children who enter daycare beyond six months of age had more initial health problems resulting in delayed start of daycare and that these children were, therefore, at increased risk for developing infections. We, however, think that this is not very likely since the WHISTLER population is relatively healthy; children born pre-term, with congenital abnormalities or neonatal respiratory diseases were excluded at baseline. To gain more insight into the severity of URTI and AOM in daycare attendees at different ages, additional relevant aspects of disease episodes should be investigated in future studies, such as episode duration and severity of symptoms.

The major strength of our study on the long-term effects of daycare on GP-diagnosed URTI and AOM episodes and related healthcare resource use is the large sample size and the prospective data collection. Information on URTI and AOM episodes was collected independently of exposure status, which minimizes information bias. Still some methodological limitations should be considered. Firstly, the information collected on daycare attendance did not include data on the type of daycare facility or group size. Previously, large daycare group size was found to increase infection rates at early age [8, 9, 28, 31] and, according to Cote et al., protect against infections during elementary school years [15] when compared to children cared for at home. Furthermore, Morrissey et al. showed that children attending multiple daycare arrangements experience more respiratory problems [32]. Due to the lack of contrast in our study, the effect of daycare attendance might be underestimated for children attending large-group or multiple daycares and overestimated for small-group daycare attendees. Secondly, we cannot make inference to the long-term effects of daycare entry after the age of one year since data on daycare attendance beyond the first year of life were not available in our study. Some of the children classified in the reference group of no daycare might be exposed to daycare after their first year of life. This could lead to an underestimation of the effect of daycare. Finally, in this study, families with a high SES were overrepresented compared to the district population average. In a Swedish study, children from low SES families are less likely to attend daycare compared to children from higher SES families [18]. Indeed, the percentage of children attending daycare in this study is higher compared to the population average (approximately 80% in this study versus approximately 60% in the average Dutch population) [33]. Although this may imply selection, we consider selection bias unlikely since parents are included before the occurrence of URTI and AOM and the exposure to daycare. Furthermore, it is not plausible that the found associations between daycare attendance and the number of episodes and healthcare use for respiratory infections will differ by SES.

This study showed that children who enter daycare under the age of one year have a higher use of healthcare resources for URTI and AOM in the first six years compared to children who were cared for at home. Both groups had a similar number of GP consultations over the same period; however, the timing of infections in daycare attendees was earlier in life resulting in higher use of healthcare resources than the infections which occurred later in childhood in children cared for at home. Our findings emphasize the need for improved prevention strategies in daycare facilities to lower infection rates at the early ages. Future studies are needed to determine which prevention strategies may be most effective, for example, reduction of daycare group size or determination of an optimal age of day care entry.