Personal child and mother carbon monoxide exposures and kitchen levels: methods and results from a randomized trial of woodfired chimney cookstoves in Guatemala (RESPIRE)

Abstract

During the first randomized intervention trial (RESPIRE: Randomized Exposure Study of Pollution Indoors and Respiratory Effects) in air pollution epidemiology, we pioneered application of passive carbon monoxide (CO) diffusion tubes to measure long-term personal exposures to woodsmoke. Here we report on the protocols and validations of the method, trends in personal exposure for mothers and their young children, and the efficacy of the introduced improved chimney stove in reducing personal exposures and kitchen concentrations. Passive diffusion tubes originally developed for industrial hygiene applications were deployed on a quarterly basis to measure 48-hour integrated personal carbon monoxide exposures among 515 children 0-18 months of age and 532 mothers aged 15-55 years and area samples in a subsample of 77 kitchens, in households randomized into control and intervention groups. Instrument comparisons among types of passive diffusion tubes and against a continuous electrochemical CO monitor indicated that tubes responded nonlinearly to CO, and regression calibration was used to reduce this bias. Before stove introduction, the baseline arithmetic (geometric) mean 48-h child (n=270), mother (n=529) and kitchen (n=65) levels were, respectively, 3.4 (2.8), 3.4 (2.8) and 10.2 (8.4) p.p.m. The between-group analysis of the 3355 post-baseline measurements found CO levels to be significantly lower among the intervention group during the trial period: kitchen levels: -90%; mothers: -61%; and children: -52% in geometric means. No significant deterioration in stove effect was observed over the 18 months of surveillance. The reliability of these findings is strengthened by the large sample size made feasible by these unobtrusive and inexpensive tubes, measurement error reduction through instrument calibration, and a randomized, longitudinal study design. These results from the first randomized trial of improved household energy technology in a developing country and demonstrate that a simple chimney stove can substantially reduce chronic exposures to harmful indoor air pollutants among women and infants.

Conflict of interest statement

Conflict of interest

The authors declare no conflict of interest.

Figures

Figure 1

Mother and child by open cookfire. Child is wearing diffusion CO tube behind the left shoulder and mother on the left shoulder. Informed consent was obtained in writing for the photo.

Figure 2

(a–c) Comparisons of CO tubes between (a) duplicates; between (b) tube types; and by (c) tube type according to calibration against collocated electrochemical monitors.

Figure 3

Alternative estimates (95% confidence intervals) of the effects of the plancha chimney stove intervention on personal exposures and kitchen levels of carbon monoxide (CO). Repeated measures of 48-h CO were log-transformed and used as the dependent variable in linear mixed effects models. The models for between-groups comparisons are based on data from the trial period only and the intervention effect is estimated by including an indicator variable for randomized group. The models for the before-and-after comparisons use data from the intervention group only and the intervention effect is estimated by an indicator variable for the trial period in contrast to the baseline period. The comparison-of-change models uses data from both groups and from both the baseline and trial periods, and the main parameter of interest is the interaction between randomized group and study period, both of which are included as main effects.

Figure 4

(a–c) Trends of 48-h CO levels during RESPIRE for (a) child and (b) mother exposures and (c) kitchen concentrations by randomized group assignment. Estimated using penalized splines in generalized additive mixed models. Dashed lines represent point-wise 95% confidence intervals. Vertical dotted line represents time of stove intervention. Tick marks above x axis indicate individual measurements.