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Many epidemiological studies have examined the link between Day care – Wikipedia attendance 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 Human microbiota – Wikipedia, 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 (Acute lymphoblastic leukemia – Wikipedia) and other forms of common Childhood leukemia – Wikipedia (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 (1). 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 Hygiene hypothesis – Wikipedia, i.e., larger the family and more older siblings a child had (birth order), lower their risk for Allergic rhinitis – Wikipedia (2).
  • 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 (3), Germany (4), and the US (5) 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, 7, 8). 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 Meta-analysis – Wikipedia of 14 Case-control study – Wikipedia published in English found that daycare attendance, especially among children less than 2 years of age reduces ALL risk (9). 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 (10).
  • 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 (11). 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 (12), Denmark (13, 14), Greenland (15), 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 (20), Sweden (21, 22), Spain (23), USA (24), the Netherlands (25) 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.


1. America’s Children in Brief: Key National Indicators of Well-Being, 2016

2. Strachan, David P. “Hay fever, hygiene, and household size.” BMJ: British Medical Journal 299.6710 (1989): 1259. http://www.ncbi.nlm.nih.gov/pmc/…

3. Côté, Sylvana M., et al. “Short-and long-term risk of infections as a function of group child care attendance: an 8-year population-based study.” Archives of pediatrics & adolescent medicine 164.12 (2010): 1132-1137. http://www.fyiliving.com/wp-cont…

4. Zutavern, Anne, et al. “Day care in relation to respiratory‐tract and gastrointestinal infections in a German birth cohort study.” Acta paediatrica 96.10 (2007): 1494-1499.

5. Ball, Thomas M., et al. “Influence of Attendance at Day Care on the Common Cold From Birth Through 13 Years of Age.” Archives of Pediatrics & Adolescent Medicine 156.2 (2002): 121. Influence of Attendance at Day Care on the Common Cold From Birth Through 13 Years of Age

6. Greaves, M. F. “Speculations on the cause of childhood acute lymphoblastic leukemia.” Leukemia 2.2 (1988): 120-125.

7. Greaves, Mel. “Childhood leukaemia.” British Medical Journal 324.7332 (2002): 283. http://pubmedcentralcanada.ca/pm…

8. Greaves, Mel. “Infection, immune responses and the aetiology of childhood leukaemia.” Nature Reviews Cancer 6.3 (2006): 193-203. http://www.ittumori.it/IttSanita…

9. Urayama, Kevin Y., et al. “A meta-analysis of the association between day-care attendance and childhood acute lymphoblastic leukaemia.” International journal of epidemiology 39.3 (2010): 718-732. A meta-analysis of the association between day-care attendance and childhood acute lymphoblastic leukaemia

10. Maia, Raquel da Rocha Paiva, and Victor Wunsch Filho. “Infection and childhood leukemia: review of evidence.” Revista de saude publica 47.6 (2013): 1172-1185. http://www.scielosp.org/pdf/rsp/…

11. Rudant, Jérémie, et al. “Childhood acute lymphoblastic leukemia and indicators of early immune stimulation: a childhood leukemia international consortium study.” American journal of epidemiology (2015): kwu298. A Childhood Leukemia International Consortium Study

12. Kusel, Merci MH, et al. “Occurrence and management of acute respiratory illnesses in early childhood.” Journal of paediatrics and child health 43.3 (2007): 139-146. https://www.researchgate.net/pro…

13. von Linstow, Marie‐Louise, et al. “Acute respiratory symptoms and general illness during the first year of life: A population‐based birth cohort study.” Pediatric pulmonology 43.6 (2008): 584-593. https://www.researchgate.net/pro…

14. Kamper-Jørgensen, Mads, et al. “Population-based study of the impact of childcare attendance on hospitalizations for acute respiratory infections.” Pediatrics 118.4 (2006): 1439-1446.

15. Koch, Anders, et al. “Risk factors for acute respiratory tract infections in young Greenlandic children.” American Journal of Epidemiology 158.4 (2003): 374-384. Risk Factors for Acute Respiratory Tract Infections in Young Greenlandic Children

16. De Martino, M., and S. Ballotti. “The child with recurrent respiratory infections: normal or not?.” Pediatric Allergy and Immunology 18.s18 (2007): 13-18.

17. Dales, Robert E., et al. “Respiratory illness in children attending daycare.” Pediatric pulmonology 38.1 (2004): 64-69.

18. Bradley, Robert. “Child care and common communicable illnesses.” Archives of Pediatrics and Adolescent Medicine 155.4 (2001): 481-488).

19. Lu, N., et al. “Child day care risks of common infectious diseases revisited.” Child: care, health and development 30.4 (2004): 361-368.

20. Thrane, Nana, et al. “Influence of day care attendance on the use of systemic antibiotics in 0-to 2-year-old children.” Pediatrics 107.5 (2001): e76-e76. http://pediatrics.aappublication…

21. Hjern, A., et al. “Socio‐economic differences in daycare arrangements and use of medical care and antibiotics in Swedish preschool children.” Acta Paediatrica 89.10 (2000): 1250-1256.

22. Hedin, Katarina, et al. “Physician consultation and antibiotic prescription in Swedish infants: population‐based comparison of group daycare and home care.” Acta Paediatrica 96.7 (2007): 1059-1063.

23. del Castillo‐Aguas, Guadalupe, et al. “Infectious morbidity and resource use in children under 2 years old at childcare centres.” Journal of Paediatrics and Child Health (2016).

24. Silverstein, Michael, Anne E. Sales, and Thomas D. Koepsell. “Health care utilization and expenditures associated with child care attendance: a nationally representative sample.” Pediatrics 111.4 (2003): e371-e375. https://www.researchgate.net/pro…

25. de Hoog, Marieke LA, et al. “Impact of early daycare on healthcare resource use related to upper respiratory tract infections during childhood: prospective WHISTLER cohort study.” BMC medicine 12.1 (2014): 1. Impact of early daycare on healthcare resource use related to upper respiratory tract infections during childhood: prospective WHISTLER cohort study

26. Reves, R. R., and J. Jones. “Antibiotic use and resistance patterns in day care centers.” Semin Pediatr Infect Dis 1 (1990): 212-221.