Patterns of allergic sensitization and factors associated with emergence of sensitization in the rural tropics early in the life course: findings of an Ecuadorian birth cohort

Abstract

Introduction: There are limited data on emergence of allergic sensitization (or atopy) during childhood in tropical regions.

Methods: We followed a birth cohort of 2404 newborns to 8 years in tropical Ecuador and collected: risk factor data by maternal questionnaires periodically from birth; atopy was measured by skin prick test reactivity (SPT) to aeroallergens in parents, and aeroallergens and food allergens in children at 2, 3, 5, and 8 years; and stool samples for soil-transmitted helminths (STH) from children periodically to 8 years and from parents and household members at the time of recruitment of cohort children. Data on risk factors were measured either at birth or repeatedly (time-varying) from birth to 8 years. Longitudinal repeated-measures analyses were done using generalized estimating equations to estimate an the age-dependent risk of positive SPT (SPT+) to any allergen or mite during early childhood to school age.

Results: SPT+ to any allergen was present in 29.0% of fathers and 24.8% of mothers, and in cohort children increased with age, initially to mite but later to cockroach, reaching 14.8% to any allergen (10.7% mite and 5.3% cockroach) at 8 years. Maternal SPT+, particularly presence of polysensitization (OR 2.04, 95% CI 1.49-2.77) significantly increased the risk of SPT+ during childhood, while household overcrowding at birth decreased the risk (OR 0.84, 95% CI 0.72-0.98). For mite sensitization, maternal polysensitization increased (OR 2.14, 95% CI 1.40-3.27) but rural residence (OR 0.69, 95% CI 0.50-0.94) and birth order (3^rd -4^th vs. 1^st - 2^nd: OR 0.71, 95% CI 0.52-0.98) decreased the risk. Time-varying exposures to agricultural activities (OR 0.77, 95% CI 0.60-0.98) and STH parasites (OR 0.70, 95% CI 0.64-0.91) during childhood decreased while anthelmintics increased the childhood risk (OR 1.47, 95% CI 1.05-2.05) of mite sensitization.

Conclusion: Our data showed the emergence of allergic sensitization, primarily to mite and cockroach allergens, during childhood in tropical Ecuador. A role for both antenatal and postnatal factors acting as potential determinants of SPT+ emergence was observed.

Keywords: allergic sensitization; atopy; childhood; cohort; risk factors; tropics.

Figure 1

Flow diagram to show follow-up of cohort to 8 years and allergen skin prick testing. Denominator for all proportions is 2,404. A child with any SPT result during follow-up was included in the longitudinal analysis.

Figure 2

Percentages of mothers, fathers, and cohort children (at 8 years) with positive skin prick tests (SPT+) to any allergen and individual allergen extracts. Data for Mothers (n = 2,031) (blue bars), fathers (n = 1,191) (orange bars), and children at 8 years (n = 1,952) (gray bars).

Figure 3

Changes in allergic sensitization profiles between 2 and 8 years of age in cohort. Bars represent 2 (blue), 3 (orange), 5 (gray), and 8 (yellow) years. Perennial allergens included mite, cockroach, dog, and cat allergens.

Figure 4

Age-dependent proportions of cohort children with allergen skin prick test positivity (SPT+) to any allergen (blue) and to mite (green). Shown are predictions from population average longitudinal models (predictions shown by solid lines and 95% confidence intervals by dotted lines) against raw data percentages (bars).

Figure 5

Effects of number of maternal allergen skin prick test positive (SPT+) reactions on age-dependent proportions of cohort children with SPT+ to any allergen and to mite. Shown are predictions from population average longitudinal models (predictions shown by solid lines and 95% confidence intervals by dotted lines) against raw data percentages (bars) stratified by maternal sensitizations. Blue lines/bars−0 maternal SPT+ reactions; green lines/bars−1 SPT+ reaction; orange lines/bars—two or more SPT+ reactions.

Figure 6

Effect of maternal infections with any soil-transmitted helminth (STH) parasites or with specific STH species on age-dependent proportions of cohort children with allergen skin prick test positivity (SPT+) to mite. Shown are predictions from population average longitudinal models (predictions shown by solid lines and 95% confidence intervals by dotted lines) against raw data percentages (bars). Blue lines/bars—children of uninfected mothers; green lines/bars—children of infected mothers.

Figure 7

Effect of childhood soil-transmitted helminth (STH) parasites or with specific STH species on age-dependent proportions of cohort children with allergen skin prick test positivity (SPT+) to mite. Shown are predictions from population average longitudinal models (predictions shown by solid lines and 95% confidence intervals by dotted lines) against raw data percentages (bars). Blue lines/bars—uninfected children; green lines/bars—infected children.