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Early life exposure to infections and risk of childhood acute lymphoblastic leukemia
Kevin Y Urayama1, Xiaomei Ma, Steve Selvin
1School of Public Health, University of California, Berkeley, CA, USA. urayamak@fellows.iarc.fr
Insights
Early life infections, like daycare attendance and ear infections, may protect against childhood acute lymphoblastic leukemia (ALL). These protective effects varied by ethnicity, with ear infections showing consistent benefits.
Area of Science:
- Epidemiology
- Pediatric Oncology
- Immunology
Background:
- Growing evidence suggests early-life infections may reduce the risk of childhood acute lymphoblastic leukemia (ALL).
- Sociodemographic differences between ethnic groups may influence the relationship between infection exposure and ALL risk.
Purpose of the Study:
- To examine the association between daycare attendance, birth order, and infant infections with ALL risk in non-Hispanic white and Hispanic children.
- To investigate ethnic variations in the protective effects of early-life infection exposures against childhood leukemia.
Main Methods:
- Case-control study including 669 ALL cases and 977 controls aged 1-14 years from the Northern California Childhood Leukemia Study (NCCLS).
- Analysis of three infection exposure measures: daycare attendance, birth order, and infant ear infections.
- Evaluation of exposures individually and simultaneously, stratified by ethnicity (non-Hispanic white and Hispanic).
Main Results:
- Daycare attendance and having an older sibling were associated with reduced ALL risk in non-Hispanic white children, but not Hispanic children.
- Infant ear infections showed a protective effect against ALL in both non-Hispanic white and Hispanic children.
- Simultaneous assessment strengthened the protective associations for daycare and older siblings in non-Hispanic whites, while ear infection protection persisted in Hispanics.
Conclusions:
- Early-life infection exposures, including daycare and ear infections, appear to play a protective role against childhood acute lymphoblastic leukemia.
- Ethnic differences exist in the protective associations of infection exposures, highlighting the importance of considering ethnicity in leukemia research.
- Findings support the infection hypothesis for childhood leukemia across diverse populations.
Abstract:
Evidence from a growing number of studies indicates that exposure to common infections early in life may be protective against childhood acute lymphoblastic leukemia (ALL). We examined the relationship between three measures of early life exposure to infections-daycare attendance, birth order and common childhood infections in infancy-with the risk of ALL in non-Hispanic white and Hispanic children, two ethnicities that show sociodemographic differences. The analysis included 669 ALL cases (284 non-Hispanic whites and 385 Hispanics) and 977 controls (458 non-Hispanic whites and 519 Hispanics) ages 1-14 years enrolled in the Northern California Childhood Leukemia Study (NCCLS). When the three measures were evaluated separately, daycare attendance by the age of 6 months (odds ratio [OR] for each thousand child-hours of exposure = 0.90, 95% confidence interval [CI]: 0.82-1.00) and birth order (OR for having an older sibling = 0.68, 95% CI: 0.50-0.92) were associated with a reduced risk of ALL among non-Hispanic white children but not Hispanic children, whereas ear infection before age 6 months was protective in both ethnic groups. When the three measures were assessed simultaneously, the influence of daycare attendance (OR = 0.83, 95% CI: 0.73-0.94) and having an older sibling (OR = 0.59, 95% CI: 0.43-0.83) became stronger for non-Hispanic white children. In Hispanic children, a strong reduction in risk associated with ear infections persisted (OR = 0.45, 95% CI: 0.25-0.79). Evidence of a protective role for infection-related exposures early in life is supported by findings in both the non-Hispanic white and Hispanic populations within the NCCLS.
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