NEW HAVEN, CONN—Studies of the health effects of wood stoves and other secondary indoor heat sources have produced inconsistent findings. However, the latest investigation strongly suggests that several of these heat sources contribute to a modest but significant rise in the incidence of upper and lower respiratory symptoms in infants.[1]

In the new study, 890 infants were observed to assess the relationship between secondary heat sources and cough and wheeze during the first year of life. Of the four heat sources evaluated, gas space heaters were associated with an increase in days and episodes of wheeze, kerosene heaters were linked to an increase in cough episodes, and wood stoves appeared to increase the number of days with cough.

No significant relationship emerged between fireplace use and cough or wheeze, although the reason for that is unclear. “Infant exposure to particulate matter from fireplaces may not have occurred much because fireplaces tend to be used after infants are put to bed [and] for relaxation rather than for heating,” suggested lead investigator Elizabeth W. Triche, PhD, Associate Director of Data Analysis and Management at the Yale Center for Perinatal, Pediatric, and Environmental Epidemiology in New Haven, Conn.

BIWEEKLY DATA COLLECTION IMPROVED ACCURACY

The study data were obtained by questionnaire from women who gave birth at any of 12 hospitals in Connecticut and Virginia between 1993 and 1996. Each day, the women recorded whether their infants coughed or wheezed and relayed this information, along with information about any secondary heat source exposure, to investigators during biweekly telephone interviews.

The investigators excluded households with smokers from the study to eliminate the effect of smoking on infant respiratory symptoms.

SYMPTOMS INCREASED WITH USE

The proportions of households that used a fireplace, kerosene heater, wood stove, or gas space heater at least once during the study were 25%, 18%, 17%, and 3%, respectively. Use of these heat sources was intermittent, the study findings confirmed.

Although most of the infants did not cough or wheeze during every biweekly period, 88% had at least one day of cough and 33% had at least one day of wheeze during the winter heating season in their first year of life. During biweekly periods in which respiratory symptoms were reported, the infants had a median of 4.4 days and 1.2 episodes of cough and 3.7 days and 1.1 episodes of wheeze.

In an adjusted statistical analysis, gas space heaters caused the number of days and episodes of wheeze to rise by about 25% for every eight additional hours of daily use. With the same amount of use, wood stoves increased the number of days with cough by 10%, and kerosene heaters increased the number of cough episodes by 7%.

Parents with infants who develop respiratory symptoms should consider secondary heat sources as a possible cause and make sure that such heat sources are properly vented, Dr. Triche advised. “More research is needed to determine if changing an infant’s exposure to secondary heat sources would prevent some of these respiratory symptoms from developing,” she added.

—Timothy Begany