Many epidemiological studies have examined the link betweenattendance and illness. Problem is by a priori choosing to document/assess/quantify daycare-associated infections makes such examinations less neutral since they equate infections, an undesirable event, with microbial exposure, a plausibly neutral event. Thus, rather than daycare attendance being a proxy for increased microbial exposure per se which is what they actually are, they’ve largely been examined as a proxy for infections.
However, in the age of, we increasingly appreciate that microbial exposure and infections are decidedly not the same. Rather, more frequent, more complex and greater microbial exposure in childhood may even be beneficial in the long-term. Thus, synthesizing the vast amount of information generated by these numerous epidemiological studies yields a decidedly mixed bag since the intent of many older studies is largely distorted by the flawed conflation of microbes and infections.
Keeping that glaring caveat in mind, with respect to protection, epidemiological data from various countries suggest daycare attendance reduces risk for ALL () and other forms of common (CL), and for common cold and ear infections. On the other hand, data also shows children in daycare can experience more frequent acute respiratory tract infections (RTI) as well as greater number of doctor visits and antibiotic prescription rates compared to those in home care.
Childhood Infection Risks: Daycare Attendance One Of Many Factors
Over the course of the 20th century and beyond, more and more children the world over attend formal daycare. For example, >60% of US children aged 0 to 6 (). Consequences of this early life difference are less clear because there are many other important confounding factors. These include
- Age of daycare entry. Those who enter daycare after 1 year of age tend to get less sick.
- Whether or not the child was born at term. Pre-term birth increases infection risk.
- Whether the child was born through vaginal or C-section delivery. Lower risk of later life allergies and autoimmunities with vaginal delivery.
- Whether or not the child has older siblings. More older siblings, lower the risk of later life allergies and autoimmunities (the original hygiene hypothesis). David P. Strahan followed >17000 children for >23 years and in 1989 first proposed what eventually became known as the , i.e., larger the family and more older siblings a child had (birth order), lower their risk for ( ).
- Whether the child was exclusively breast-fed or not, at least during the 1st 3 to 4 months of life. The former are better protected against infections, especially upper respiratory tract infections.
- Whether the child is exposed or not to pets at home. Pet exposure seems to protect against some allergies and infections.
- Parental age. Younger better for the child, presumably because younger egg and sperm carry fewer deleterious genetic and epigenetic changes.
- Parental life-history. Parental smoking, especially during pregnancy, increases child’s risk for asthma and allergies.
Beneficial Consequences Of Daycare Exposure
Epidemiological studies from Canada (), Germany (4), and the US ( ) suggest early life daycare is associated with protection against common cold and ear infection during some of the later school years.
Daycare Exposure & Protection From Childhood Cancer
According to the ‘delayed infection hypothesis’ proposed by Mel Greaves, early life ‘common’ infections could be protective against ALL, the idea being limited infections at this early life stage increase risk of abnormal immune responses to the same infections later on and some of these abnormal immune responses could trigger the B cell mutations characteristic of ALL (6,, ). Even though childhood leukemias have well-defined genetic susceptibility, according to Greaves, rather than infections per se, their timing crucially impacts ALL risk. Earlier the infections, lower the risk. The underlying idea is the newborn immune system is evolutionarily programmed to ‘learn’ through infectious life history early in life. Of course, now it’s more appropriate to revise this view and argue instead that sequence, frequency and timing of exposure to microbes in early life is crucial to well-regulated immune function throughout life.
Indeed a preponderance of epidemiological evidence suggests children who attend daycare starting early in life are less likely to develop ALL.
- Using daycare attendance as a proxy for exposure to infectious agents, a of 14 published in English found that daycare attendance, especially among children less than 2 years of age reduces ALL risk ( ). The fact that these studies were conducted by different teams in different countries (1 each in Canada, Denmark, Germany, New Zealand and Hong Kong, 2 each in France, Greece, UK, and 3 in USA) only strengthens the data set.
- Another meta-analysis of largely the same studies also concluded it reduced risk of childhood leukemia ( ).
- Another thorough meta-analysis assessed a total of 11 case-control studies (1 each from Australia, Canada, Greece, Italy, New Zealand, UK, 2 from USA, and 3 from France), i.e., a total of 7399 ALL cases and 11181 controls aged 2 to 14 years ( ). It too found an inverse association between ALL and daycare attendance, especially lower risk for children who started daycare at an earlier age.
The fact that these analyses found ALL risk didn’t correlate with specific infections in infancy suggests that risk mitigation may be more a case of more exposure to diverse microbes and maybe the body learning to make well-regulated immune responses to them rather than exposure to specific infections per se.
Adverse Consequences Of Daycare Exposure
Several studies have shown children in daycare experience higher infection rates compared to those not in daycare.
- As illustrative examples, epidemiological studies from Australia ( ), Denmark ( , 14), Greenland ( ), Italy (16) and Canada (17) show children in daycare experience more frequent acute respiratory tract infections (RTI) compared to those in home care.
- However, some studies (18, 19) suggest such differences are most pronounced in the first two years of life and tend to fade away to no difference between the two groups by the 3rd year of life.
- Also, one study (14) suggests risks were much higher for babies living in homes with no other children.
- Epidemiological studies from Denmark ( ), Sweden (21, 22), Spain (23), USA ( ), the Netherlands ( ) have noted greater doctor visits and antibiotic prescription rates for daycare attendees. In fact, already back in 1990, a US study had noted 2.4 to 3.6 times higher antibiotic prescription rates for children in daycare compared to those cared for at home (26).
Clearly, these data suggest care-givers and physicians haven’t yet heeded the clarion call to limit antibiotic use. Clearly, public health officials and scientists, microbiologists in particular, need to exert more effort in ensuring this counter-productive practice abates.
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