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Cotinine to Creatinine Ratios Lowered Only in Infants Residing in Homes That Ban Tobacco Smoking

Infants living in homes that do not permit indoor tobacco smoking have significantly lower urinary cotinine to creatinine ratios than infants who reside where smoking is permitted according to the findings from a cross sectional survey of households in the United Kingdom.

Researchers report no difference in urinary cotinine to creatinine ratios among infants residing where either some or no remedies are used to reduce their exposure to environmental tobacco smoke.

"Many of the harm reduction strategies used by the parents, such as opening windows when smoking and using fans and ionisers, were ineffective," writes Claire Blackburn, senior lecturer at the University of Warwick, Coventry, United Kingdom and colleagues. They collected data from 314 households (with at least 1 smoker residing) to determine parents' knowledge and use of measures to reduce their infants' exposure to environmental tobacco smoke.

The researchers also collected a urine sample from the infants (mean age 12.8 weeks and exclusively bottle-fed) living in these households to estimate the urinary cotinine to creatinine ratios among infants exposed to different levels of environmental smoke.

Overall, 86% of the parents believed that environmental smoke is harmful and 90% understood that infants could be protected from environmental smoke in the home. Sixty-five percent of the parents reported using 2 or more measures to reduce environmental exposures, such as smoking less, not allowing smoking in the infants' location, or airing out the room during and after smoking. However only 18% of the parents banned smoking from their home.

Complete data available in 164 infants revealed mean log cotinine to creatinine ratios of 1.26 for those living in households that banned tobacco smoking and 2.58 for infants living where some or no measures were used to
reduce environmental smoke exposure. After the researchers adjusted for average household cigarette consumption, tenure, and overcrowding they found that banning smoking in the home was independently associated with a reduction in urinary cotinine to creatinine ratio of 2.6.

"Harm reduction measures short of a total ban on smoking in the home," the researchers conclude, "are likely to have little effect on the exposure of infants to tobacco smoke."
BMJ 2003;327:7409:257-60.

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