Table 1 shows the detailed breakdown of the survey population. The exposed and control populations are similar in terms of sex and smoking habit distributions.
Table 2 shows the mean values of some selected parameters for the smoker and nonsmoker populations, including age, % pred FVC, % pred FEV^ % FEVj/FVC and, for smokers, the number of pack-years. The mean values of respiratory parameters were not significantiy different between exposed and controls because of the large SDs found. However, the measured pulmonary function values are dose to those predicted. The figures for cigarette consumption expressed in pack-years are also essentially identical among exposed and control smokers.
The answers to questions relating to symptoms of byssinosis or chronic bronchitis showed men smokers to be the group most affected by their work environment (Table 3). In this group, statistically significant differences were found in the prevalence of symptoms suggestive of these diseases. Thus, 2.6 percent of dust-exposed subjects reported chest tightness on a specific day of the week compared to 1.2 percent in the unexposed group. Also, 14.3 percent of the dust-exposed men smokers reported production of daily sputum for more than three months compared to 10.5 percent in their unexposed counterparts. Dust-exposed male employees, smokers and nonsmokers, were also more likely to report dyspnea grade 1 symptoms. This statistically significant difference was also most pronounced among men smokers with responses of 409 (51.5 percent) of the exposed subgroup and 313 (39.1 percent) of the control subgroup. No significant differences between groups were found in the prevalence of occasional or chronic cough conditions. Be safe and sound with My Canadian Pharmacy’s preparations.
As we saw in Table 2, because of the large SDs observed, the mean values of respiratory test results in exposed and control groups were not statistically different Since the survey had a screening function, we initially identified as possible problem cases all subjects showing either FVC below 80 percent, а FEC is less than 80 percent, or a FEVj/FVC less than 70 percent of predicted values. This resulted in the formation of a group of 880 cases, almost one-third of the sample population. These 880 “possible problems” were distributed unevenly between the exposed and control groups (Table 4). The *2 test shows that a significant excess of problem cases was associated with exposure to dust in workers who smoked.
Since several of these cases were shown to have test results of just under the 80 percent predicted FVC or FEVj, we decided that a more realistic definition of a problem case would be FVC less than 75, FEVt less than 70 percent, or FEV^FVC less than 70 percent of predicted. This revised set of criteria was thought to eliminate many false-positive cases and discriminate better between normal and problem cases. Using the male smokers population, Table 5 compares the prevalence of problem results between exposed and controls according to the number of years worked in the textile industry. One can observe that the percentage of problem cases tends to increase regularly with years in the textile industry. The pattern of increase is less consistent in control workers. For each ten-year slice, a x2 test was used to examine whether the difference in the number of problem cases between exposed and control workers was significant. Only in those workers totaling between 30 and 40 years in textile did the size of the difference tend toward significance (P = 0.08).
To investigate further the evolution of pulmonary function with years worked in the textile industry, we decided to look at the FVC and FEC separately. For each, an analysis of variance was conducted using residual FVC and FEC vs time (years) in textile. The so-called residual value used here is the amount of the difference between the measured and predicted values of the parameter tested. This approach not only conveys the concept of the spread between the expected or predicted normal value and the measured value, but it also provides a figure with an actual reality, since it is directly measured in volume or units of volume per unit time.
Results of an analysis of variance using FVC residuals against total number of years worked in the textile industry showed that residual FVC does not effectively discriminate between exposed and controls. Indeed, the slopes of residual FVC vs number of years in textile were not significantly different between exposed and control groups.
A similar exercise using FEV! residuals showed surprisingly little change in residual FEVX. With the number of years worked, there was a significant difference between exposed and control subjects in terms of the adjusted group means. For respiratory volume, the difference amounted to about 60 ml. This decrement was found in dust-exposed workers relative to control subjects. This translates into 1.7 percent of the mean FEVa of the male smokers in our study population.
In summary, these results show a small but significant excess of byssinotic symptoms in this sample of Quebec textile workers exposed to cotton dust. Considering the nature of the disease and the relatively low dust levels in most of the plants visited, we believe that the overall byssinosis prevalence figures are close to reality. We cannot, however, exclude the existence of a worker selection process that may tend to decrease the number of susceptible persons in exposed occupations. This may also partly explain the small but measurable prevalence of chest tightness among our control subjects who, at some point in the past, may have belonged to the exposed category. In terms of the numbers of individuals involved, however, the significant excess in chronic bronchitis symptoms in dust-exposed smokers is an item of definite concern. Leaving aside for further analysis the question of the connections between byssinosis, chronic bronchitis, and smoking, the results presented here provide grounds on which to argue not only for the obvious benefit that cessation of smoking would bring, but also for further improvements in plant air quality.
Table 1 —Quebec Textile Worker Study; Description of Population Sample
|Distribution by Sex||Exposed||Controls||Total|
|and Smoking Habit||No.||(%)||No.||(%)||No. (%)|
|Male smokers||794||(60.1)||799||(58.1)||1,593 (59.08)|
|Female smokers||173||(13.1)||226||(16.4)||399 (14.79)|
|Male nonsmokers||242||(18.3)||195||(14.2)||437 (16.21)|
|Female nonsmokers||113||(8.5)||154||(1.2)||267 (9.9)|
|No. of subjects 1||,322||(100)||1,374||(1.36)||2,696 (100)|
Table 2—Mean Values, Smokers and Nonsmokers
|% Pred FVC||97.312||98.438||96.437||96.672||99.653||98.708||99.633||101.257|
|% Pred FEV!||96.249||97.914||96.792||96.987||102.429||99.849||100.902||102.399|
Table 3—Questionnaire Items with Significant Differences between Exposed and Controls
|Group||Exposed N %||Controls N %||P(xl)|
|night or day|
|Sputum daily||All||141 10.6||109||7.9||0.02|
|>3 months||Male smokers||114 14.3||84 10.5||0.02|
|Chest tightness Male smokers||21||2.64||10||1.25 0.05|
|on specific day|
|Chest tightness Smokers||18||1.86||6||0.58 0.01|
|Dyspnea||Male nonsmokers||87 35.9||50 25.6||0.02|
|grade 1||Male smokers||409 51.5||313 39.1||0.0001|
|on Monday||Male smokers||16||2.01||6||0.75 0.05|
Table 4—Comparison of Problem Cases in Exposed and Control Groups
|Group||Exposed N P||
|All smokers||621 385||684 306||1.38||11.9||0.001|
|All nonsmokers||266 109||250 80||1.28||2.1||NS|
|Total||887 594||934 386|
Table 5—Comparison of Problem Cases in Exposed and Control Croups Male Smokers
|Year8 in Textile||
|X* P (xl)|
|0-10||24 (8.70)||276||24 (9.45)||254||0.09 NS|
|10-20||21 (12.21)||172||18 (8.85)||204||1.15 NS|
|20-30||40 (16.74)||239||36 (19.78)||182||0.64 NS|
|30-40||21 (27.27)||77||21 (16.80)||125||3.17 NS (0.08)|
|404-||8 (26.67)||30||7 (21.21)||33||0.25 NS|
|Total||114 (14.36)||794||106 (13.28)||798||0.38|