Abstract
Background
In recent decades New Zealand has seen a growth in the use of childcare as a weekday living environment for children under five years old, with an increasing proportion of children attending, and children attending for longer hours. For children in early education or care, New Zealand has one of the lower allocations of indoor activity space per child in the OECD, at 2.5m2 per child. The New Zealand minimum indoor temperature requirement for these environments is 16oC, the lowest found in a search of English-language statutes and recommendations. With one exception, all other recommendations or requirements found were 18oC or more. New Zealand research has found a positive association between higher rates of respiratory and gastrointestinal infections, and colder temperatures and crowding in dwellings, while four studies outside New Zealand reported negative association between illness rates and greater area per child in childcare. Viral infectivity has been shown to decrease with higher environmental temperatures.
Methods
A 22-week observational cohort study was conducted in winter-spring 2017 measuring temperatures, humidity, child illness rates and rates of absence from childcare, and consequent parental absence from work. The study involved 22 full-day childcare centres, and a final cohort for statistical analysis of 221 children aged two to five years old. The study geographic area was the Hutt Valley and nearby suburbs, in the Wellington region of New Zealand. Indoor temperature and humidity were measured at 15-minute intervals, while activity space per child was calculated from floor area measurement and Ministry of Education daily attendance data. Symptomatic illness data and absence data were obtained from website-based reports entered by parents. Data were analysed by generalised linear mixed modelling to account for clustering by childcare centre, to generate rate ratios (RR) of child-days sick in relation to environmental variables.
Results
The study found a significant negative relationship between increased indoor temperatures in childcare and child-days sick. For each degree increase in the median winter indoor temperatures, risk was reduced by 28%, RR = 0.721 (95% CI: 0.563 to 0.924). The association was significant across the second and third quartile temperature ranges, which were from 15.2oC to 20.8oC. For each percentage point of time spent under 18oC, risk of children being away sick increased 1.5% (95% CI: 0.6% to 2.4%). The modelling controlled for mould in the child’s home, ethnicity, use of a Community Services Card (a proxy for low income), and child age. The study also found high levels of non-compliance with minimum temperature and minimum area-per-child legal requirements. Surprisingly, the analysis indicated an association between increased risk of illness and more square metres of space per child: winter-spring RR 2.132 (95% CI:1.222 to 3.720). The result was affected by multicollinearity however, and potential confounding between space per child and temperature. After removing one environment that was an outlier for illness rates and space per child, the winter result became statistically insignificant (95% CI: 0.904 to 1.376), but there was little change in the winter-spring result. This result is contrary to the four studies mentioned above, while the only other comparable study found in the literature review found no association between area per child and illness rates.
Conclusions
The results support an increase in the minimum indoor temperature requirement to 18oC, in line with WHO recommendations. The study also indicates a need to improve compliance with environmental legal minima in the New Zealand childcare sector. The analysis suggested that more space per child is a risk for illness, but this result is inconsistent with other studies, and lacks a direct mechanism for causation. The area per child result may have arisen through use of daily attendance data to generate a proxy measurement for space per child, an approach that is unable to distinguish time spent outdoors from time spent outdoors at the childcare centre.