Vinikoor et al. addition to interviews, medical tests includ- ing spirometry were performed. Radiographs were taken on individuals ≥ 18 years of age at the time of the interview. More than 7,000 current and former community members were interviewed. All participants provided informed consent under a protocol approved by the institutional review board of the Centers for Disease Control and Prevention. Further details on the study can be found elsewhere (Peipins et al. 2003). For this study we included only those ≤ 18 years of age at the time of the mine’s closure (1990; n = 1,224). At the time of the ATSDR study, the age of these individuals ranged from 10 to 29 years. We were inter- ested in studying community-based exposures rather than occupational exposures, so we excluded any individuals that responded they had a) worked for W.R. Grace, b) worked as a contractor for W.R. Grace, c) ever been exposed to dust at other jobs, or d) ever been exposed to vermiculite at other jobs (n = 221). In the questionnaire, individuals were asked if they had ever participated in six Table 1. Characteristics of study participants in 2000–2001 living in Libby, Montana, who were ≤ 18 years of age when the mine closed in 1990. Residing with someone else who smokes Characteristic Demographics Current age (years) 10–16 17–22 23–29 Sex Male Female Smoking use Never Former Current Symptom history Usually have a cougha Yes No Yes No Yes No Yes No Yes No Coughed up phlegm that was bloody in the past year Troubled by shortness of breath when walking up a slight hill or when hurrying on level grounda Been told by a physician that you have a lung disease/ condition Spirometry resultsa Normal Obstructive Restrictive Mixed 1034 aMissing data for “usually have a cough” (n = 1), “trou- bled by shortness of breath when walking up a slight hill or when hurrying on level ground” (n = 1), and spirometry results (n = 13). n (%) 495 (49.4) 304 (30.3) 204 (20.3) 429 (42.8) 574 (57.2) 772 (77.0) 73 (7.3) 158 (15.8) 508 (50.7) 495 (49.4) 108 (10.8) 894 (89.2) 59 (5.9) 944 (94.1) 145 (14.5) 857 (85.5) 51 (5.1) 952 (94.9) 896 (90.5) 62 (6.3) 30 (3.0) 2 (0.2) activities related to vermiculite exposure, including handling vermiculite insulation, par- ticipating in recreational activities along Rainy Creek Road (the road leading to the mine that at the time was gravel and was later found to be contaminated with mine tailings), playing at the ball fields (which were located near the expansion plant where there were large piles of vermiculite), playing in or around the ver- miculite piles, heating the vermiculite to make it expand/pop, and participating in other activities resulting in contact with vermicu- lite insulation, products, or ores. Responses to the questions about activities were given as “never,” “sometimes,” or “frequently.” In addition, we created an exposure variable cat- egorizing the combination of the above listed activities into never participating in any of the activities, participating only sometimes in any of the activities, participating frequently in one or two of the activities, and participating frequently in three or more of the activities. First, we determined the prevalence of cough [defined as “having a cough on most days (at least four days out of the week)”] in our study population. For comparative pur- poses, we also determined rates of similar respiratory symptoms (cough, defined as “usu- ally cough[ing] on most days for three con- secutive months or more during the year”) among individuals of the same age across the United States. This was done using the weighted National Health and Nutrition Examination Survey (NHANES) database from 2001–2002, which corresponds closely to the years of the ATSDR study (Centers for Disease Control and Prevention 2009). The definitions for cough vary slightly between the two databases. Other self-reported respiratory symptoms had greater discrepancies between definitions from the ATSDR survey and NHANES. Therefore, we did not attempt any comparisons beyond that of “usual” cough. We performed unconditional logistic regression on our study population examin- ing multiple self-reported symptoms (usually having a cough, coughing up bloody phlegm in the past year, being troubled by shortness of breath when walking up a slight hill or when hurrying on level ground, and having a physician-diagnosed lung disease or condi- tion) and responses to the six questions about activities related to potential vermiculite expo- sure. Information on respiratory symptoms was acquired with yes/no questions included in ATSDR’s questionnaire. We controlled the analyses for sex, age, smoking status (never, former, and current), and family smoking sta- tus (living/lived in a household with a smoker, not living/never lived in a household with a smoker). Using likelihood ratio tests to com- pare all models, effect measure modification was assessed for having lived with an indi- vidual while he or she was employed by W.R. Grace. No effect measure modification was seen, so no interaction terms were retained in the final models. This variable was also assessed for confounding using backward elimination with a 10% change-in-estimate criterion. We ran a second set of logistic regression models with the same exposures but using the results of spirometric testing as the outcome. Spirometry was performed using guidelines of the American Thoracic Society (1995). Results rated as “acceptable” or “suboptimal” were retained but results rated “questionable” or “uninterpretable” were excluded (American Thoracic Society 1995). Predicted values were calculated based on the lower limit of normal (LLN) using published reference equations (Hankinson et al. 1999). The results were classified as normal [forced expiratory volume in 1 sec/forced vital capacity (FEV1/FVC) ≥ LLN and FVC ≥ LLN], restrictive (FEV1/ FVC ≥ LLN and FVC < LLN), obstructive (FEV1/FVC < LLN and FVC ≥ LLN), or mixed (FEV1/FVC < LLN and FVC < LLN). Because of limitations in sample size, we col- lapsed these categories to normal and abnor- mal (restrictive, obstructive, and mixed). Again, we controlled for age, sex, and tobacco exposure (personal and family smoking sta- tus). Results of radiographs are not included here because almost half the study population did not have a radiograph and the results on those ≥ 18 years at the time of the ATSDR study in 2000–2001 were reported in a previ- ous study (Peipins et al. 2003). Results A total of 1,224 individuals included in the ATSDR survey were ≤ 18 years of age at the time of the mine closure. At the time of the ATSDR survey, the age range of study participants was 10–29 years. Two hundred twenty-one individuals worked for W.R. Grace, worked as a contractor for W.R. Grace, had been exposed to dust at other jobs, and/or had been exposed to vermiculite at other jobs and were therefore excluded from the study (of these 68.3% were men). The remaining study population contained 1,003 individ- uals, most of whom were women (57.2%) (Table 1). The data were essentially complete for all participants (see Table 1 note). Most individuals reported never smoking, but 7.3% of study participants stated that they were for- mer smokers, and 15.8% stated that they were current smokers. A small number of individu- als had abnormal spirometry results, but other respiratory symptoms, such as usually having a cough or being troubled by shortness of breath when walking up a slight hill or hur- rying on ground level, were reported with greater frequency (5.1–14.5%). Overall the prevalence of usually having a cough was 10.8% [95% confidence interval (CI), 8.9–12.7%] in Libby compared with ovlume 118 | number 7 | July 2010 • Environmental Health Perspectives