Radon Testing in Households with a Residential Smoker -- United States, 1993-1994

Epidemiologic investigations of underground miners (1) and studies of alpha particle carcinogenesis among laboratory animals (2) suggest that exposure to the radioactive decay products (progeny) of radon is an important risk factor for lung cancer. Persons who smoke cigarettes and are exposed to these radon progeny have a substantially greater risk for developing malignancy than nonsmokers (3). Residential radon concentrations above the U.S. Environmental Protection Agency's (EPA) action level of 4 pCi/L are the primary sources of exposure among the general population (4). EPA and the Public Health Service promote home testing for radon, especially in households with a person who smokes. However, it is unknown whether households that contain smokers are more likely than those without smokers to test for radon. To characterize radon testing practices of households that contain a person who smokes within the dwelling (i.e., residential smoker), CDC analyzed survey data from the National Health Interview Survey (NHIS). This report summarizes the results of this analysis, which indicates that households with a residential smoker are significantly less likely to test for radon than those without smokers.

NHIS collects information on various health issues using an annual probability sample that is representative of the civilian, noninstitutionalized population of the United States. Radon testing and radon awareness data were collected through a personal interview with one randomly selected adult (aged greater than or equal to 18 years) per household as part of the NHIS Year 2000 Supplements during 1990, 1991, 1993, and 1994. For this investigation, data from the 1993 and 1994 NHIS Year 2000 Supplements were combined and merged with the 1993 and 1994 NHIS household records to allow analysis at the household level (n=40,766). The results presented in this report are the mean values for the 1993 and 1994 NHIS Year 2000 Supplements combined. Response rates for the two survey years were 81.2% and 79.5%, respectively.

Radon testing data were derived from responses to the question "Has your household air been tested for the presence of radon?" Data representing the presence of a residential smoker were derived from responses to the question "Does anyone who lives here smoke cigarettes, cigars, or pipes anywhere inside this home?" Trailer homes and mobile homes and apartments or condominiums above the second floor were excluded (n=5801) because of their negligible radon exposure risk. A total of 34,965 households were considered at-risk for radon exposure.

The NHIS radon testing question was asked only of households that reported knowledge of radon. However, assuming that households without knowledge of radon did not have their residences tested, it is possible to calculate radon testing estimates for all households. This analysis included all households; however, it also provides radon testing estimates restricted to households with knowledge of radon, for comparison. The analyses for all households and households with knowledge of radon were calculated using SUDAAN and were weighted to produce national estimates.

During 1993-1994, an overall mean of 5.5 million (6.7%) households tested for radon (Table 1). This number of households included approximately 11.7 million persons.

Households that contained a residential smoker were significantly less likely to have tested for radon than households that did not contain a residential smoker (5.9% versus 7.1%, respectively). Differences were significant for the crude association (odds ratio [OR]=0.81; 95% confidence interval [CI]=0.74-0.90) and when controlling for household level of education, poverty status, geographic region, residence location, and presence of children (adjusted OR=0.88; 95% CI=0.79-0.97).

When the analysis was restricted to households that reported knowledge of radon (n=24,782), the percentage of households that tested for radon increased to 9.4%. Among households that contained a residential smoker, 8.3% tested for radon, and among households that did not contain a smoker, 9.8% tested. Differences were significant for both the crude association (OR=0.83; 95% CI=0.75-0.92) and when controlling for relevant covariates (adjusted OR=0.87; 95% CI=0.79-0.96).

Reported by: Illness and Disability Statistics Br, Div of Health Interview Statistics, National Center for Health Statistics, CDC.

Editorial Note:

Each year, approximately 10%-14% of lung cancer deaths in the United States are attributable to indoor radon (5), making residential exposure the second leading single cause of lung cancer. The risk for malignancy increases in the presence of cigarette smoking because of a synergistic relation between indoor radon and cigarette smoking, an effect-modifying association that is characterized as submultiplicative. Although the biologic basis for the interaction between cigarette smoking and residential radon is unclear, smoking may promote radon-initiated cells (6), implying that initial exposure to radon may increase the susceptibility of lung cells to the harmful effects of smoking.

The Public Health Service and EPA encourage persons to determine their exposure to residential radon and to reduce high levels, especially in households that contain persons who smoke. One of the national health objectives for 2000 is to increase to at least 40% the proportion of homes in which homeowners or occupants have tested their home for radon and have found either negligible risk or have modified the dwelling to reduce risk (objective 11.6) (7). In addition, the objective seeks to increase radon testing to at least 50% in high-risk households containing cigarette smokers. The findings in this report suggest that these goals probably will not be met.

The findings in this report are subject to at least three limitations. First, some respondents might not have been able to recall whether their homes had been tested for radon, resulting in reporting errors. Second, this investigation classified the smoking status of the household by asking whether the household contained a person who smoked within the dwelling; however, it did not assess whether a household contained a smoker who chose not to use tobacco products within the dwelling. An estimated 16.3% of adult smokers do not smoke within their residences (1995-1996 Current Population Survey, unpublished data, 1999). Identifying smokers who did not smoke in their dwelling would have provided a more complete picture of household smoking status, but the 1993 and 1994 NHIS did not allow this analysis. Finally, the analysis was limited to cigarette smoking, but the NHIS included smokers of all types of tobacco.

Radon testing and mitigation practices need to improve in the United States, overall and among high-risk households that contain residential smokers. The most effective means of reducing risk for radon-related lung cancer in these households is to encourage the smoker to stop using tobacco products (3,8,9). However, to maximize lung cancer risk reduction, smokers in residences with high radon concentrations should quit smoking and reduce high radon levels (8). The National Research Council (5) estimates that eliminating indoor radon exposures that are in excess of the EPA's action level would prevent approximately 30% of radon-attributable lung cancer deaths, and of these, 86% would be among persons who have ever smoked during their lifetimes. The findings in this report underscore the importance of programmatic efforts aimed at improving radon testing and mitigation practices, particularly among households that contain a residential smoker.

References

1. Lubin JH, Boice JD Jr. Lung cancer risk from residential radon: meta-analysis of eight epidemiologic studies. J Natl Cancer Inst 1997;89:49-57.
2. Gilbert ES, Dagle GE, Cross FT. Analysis of lung tumor risks in rats exposed to radon. Radiat Res 1996;145:350-60.
3. Lubin JH, Steindorf K. Cigarette use and the estimation of lung cancer attributable to radon in the United States. Radiat Res 1995;141:79-85.
4. Axelson O. Cancer risks from exposure to radon in homes. Environ Health Perspect 1995;103: 37-43.
5. National Academy of Sciences. Biological effects of ionizing radiation (BEIR) VI report: the health effects of exposure to indoor radon. Executive summary. Available at http://www.epa.gov/iaq/radon/beiriv1.html. Accessed February 19, 1998.
6. Thomas D, Pogoda J, Langholz B, Mack W. Temporal modifiers of the radon-smoking interaction. Health Physics 1994;66:257-62.
7. US Department of Health and Human Services. Healthy people 2000 review, 1997. Hyattsville, Maryland: US Department of Health and Human Services, 1997.
8. Mendez D, Warner KE, Courant PN. Effects of radon mitigation vs smoking cessation in reducing radon-related risk of lung cancer. Am J Public Health 1998;88:811-2.
9. Ford ES, Kelly AE, Teutsch SM, Thacker SB, Garbe PL. Radon and lung cancer: a cost-effectiveness analysis. Am J Public Health 1999;89:351-7.

TABLE 1. Weighted percentage of households that tested for radon, by presence of a
person who smokes in the residence (i.e., residential smoker) and selected household
characteristics -- United States, 1993-1994*
==========================================================================================================
                            Residential smoker   No residential smoker           Total
                            -------------------  ----------------------  ---------------------
Characteristic              No.+    %     (SE&)    No.    %       (SE)    No.     %       (SE)
----------------------------------------------------------------------------------------------
Highest level education
 in the household
  <High school                67   1.8%   (0.3)    133    1.9%   (0.3)    200    1.9%    (0.2)
   High school/General
    Equivalency Diploma      554   5.4%   (0.4)    874    5.2%   (0.3)   1428    5.3%    (0.2)
  >High school               826   7.8%   (0.5)   3064    9.2%   (0.4)   3890    8.8%    (0.3)

Household poverty status@
  At or above               1280   6.6%   (0.3)   3821    7.9%   (0.3)   5101    7.6%    (0.2)
  Below                      110   3.3%   (0.5)    135    2.6%   (0.3)    246    2.9%    (0.3)
  Unknown                     56   2.9%   (0.6)    124    3.1%   (0.4)    180    3.0%    (0.4)

Geographic region
 of household
  Northeast                  445   9.2%   (0.6)   1458   13.4%   (0.6)   1903   12.1%    (0.4)
  Midwest                    491   6.9%   (0.5)   1206    8.2%   (0.6)   1698    7.8%    (0.5)
  South                      346   4.2%   (0.4)    895    5.0%   (0.3)   1241    4.8%    (0.3)
  West                       164   3.7%   (0.5)    522    3.7%   (0.5)    686    3.7%    (0.5)

Household location
  Urban                     1070   5.8%   (0.3)   2968    6.9%   (0.3)   4038    6.5%    (0.2)
  Rural                      377   6.1%   (0.6)   1112    8.0%   (0.5)   1489    7.4%    (0.4)

Children residing
 in household
  Yes                        608   6.4%   (0.5)   1848    9.0%   (0.4)   2456    8.2%    (0.4)
  No                         839   5.6%   (0.3)   2232    6.0%   (0.2)   3071    5.9%    (0.2)

Total                       1446   5.9%   (0.3)   4081    7.1%   (0.3)   5527    6.7%    (0.2)
----------------------------------------------------------------------------------------------
* This analysis included all households and excluded trailer homes and mobile homes and apartments and
  condominiums above the second floor.
+ Number of households in thousands. Columns may not add to total because of rounding.
& Standard error.
@ Poverty status based on the U.S. Department of Agriculture's economy food plan.
==========================================================================================================

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