Study design and patient population
The enrollment and follow-up procedures of the HOST have been described in detail elsewhere [4]. In brief, persons found to be seropositive for HTLV-I and HTLV-II at the time of routine or autologous blood donation in 1990–1992 at five United States blood centers were eligible for enrollment. HTLV-I and HTLV-II infection status was confirmed with type-specific serology and/or polymerase chain reaction testing. Subjects have been followed approximately every two years with health history questionnaires, physical examinations, and blood testing. At the third biennial visit in 1995–1997, we performed PFT on a randomly selected subset of HTLV-I and -II positive subjects at four of the five HOST centers (American Red Cross Blood Services Southeastern Michigan (Detroit, MI), American Red Cross Blood Services Southern California (Los Angeles, CA), Blood Centers of the Pacific (San Francisco, CA), and the Oklahoma Blood Institute (Oklahoma City, OK)). We also selected seronegative subjects at the same four centers by strata based upon the age, sex and racial distribution of the HTLV positive subjects, and asked them to undergo PFT.
PFT Procedures
In performing the PFTs, we followed standards published by the American Thoracic Society [12]. Spirometers were calibrated according to these standards, and subjects performed three forced expirations. We measured forced vital capacity (FVC) in liters, forced expiratory volume at one second (FEV1), diffusing lung capacity corrected for hemoglobin (DLCOcorr) and diffusing lung capacity corrected for hemoglobin and alveolar ventilation (DLCOcorr/VA). Each subject's best effort, as judged by the highest sum of vital capacity and FEV1 from among three expiratory efforts, was used in the analysis.
Statistical analysis
For each of the pulmonary function measures, means and 95 percent confidence intervals were calculated. The mean of each parameter was compared between the HTLV-I, HTLV-II and seronegative groups using ANOVA tests (PROC GLM). Outcome variables, FVC, FEV1, DLCOcorr and DLCOcorr/VA were all treated as continuous variables in the model. Multivariable analysis was performed using linear regression, adjusting for age (quartiles: ≤ 40, 41–47, 47–53 and 54+), gender (male or female), race/ethnicity (White, Black, Hispanic, Asian/other), smoking history (nonsmokers, ex-smokers, and current smokers) and weight (study population quartiles, ≤ 66 kg, 67–78 kg, 79–88.5 kg and ≥ 88.5 kg). The model evaluated differences in pulmonary function parameters and their statistical significance when all important confounders, such as smoking, and characteristics of the study subjects were taken into consideration. Due to the limited number of subjects, we were unable to stratify the analysis by center. Nonetheless, power calculations revealed that the study was able to detect a 10 percent difference compared to seronegatives in the parameters measured with power (1 – beta) of 0.65 to 0.85 for HTLV-I, and 0.82 to 0.96 for HTLV-II. All analyses were done using SAS (SAS version 6.12, Cary, NC).
For each of the pulmonary function measures, means and 95 percent confidence intervals were calculated. The mean of each parameter was compared between the HTLV-I, HTLV-II and seronegative groups using ANOVA tests. Multivariable analysis, adjusted for age, gender, race/ethnicity, smoking history and weight, was performed using linear regression. Due to the limited number of subjects, we were unable to stratify the analysis by center. Power calculations revealed that, relative to the seronegatives, the study was able to detect a 10 percent decrease in the parameters measured with power (1 – beta) of 0.65 to 0.85 for HTLV-I and 0.82 to 0.96 for HTLV-II. All analyses were done using SAS (SAS version 6.12, Cary, NC). The Committee on Human Research of the University of California San Francisco, San Francisco, CA, USA, has approved the study.