Prevalence and risk factors for COPD in greenhouse farmers: a large, cross-sectional survey of 5,880 farmers from northeast China

Figures & data

Figure 1 Responses to the questionnaire and spirometry.

Table 1 Smoking status of responders by region, sex, age, and greenhouse type

Characteristics	Total (n)	Nonsmoker	Current smoker	Pack-years
				1–14	15–29	≥30
Region
Plain	2,981	1,934 (64.9)a	1,047 (35.1)	24 (0.8)	407 (13.7)	616 (20.7)
Mountain area	1,220	783 (64.2)	437 (35.8)	10 (0.8)	184 (15.1)	243 (19.9)
Coastal area	1,219	801 (65.7)	418 (34.3)	8 (0.7)	152 (12.5)	258 (21.2)
Sex
Male	2,660	1,286 (48.3)	1,374 (51.7)	0	489 (18.4)	885 (33.3)
Female	2,760	2,232 (80.9)	528 (19.1)	42 (1.5)	254 (9.2)	232 (8.4)
Age (yr)
<40	1,732	1,000 (57.7)	732 (42.3)	0	294 (17.0)	438 (25.3)
40–49	1,734	1,223 (70.5)	511 (29.5)	0	213 (12.3)	298 (17.2)
50–59	1,571	1,114 (70.9)	457 (29.1)	0	175 (11.1)	282 (18.0)
≥60	383	181 (47.3)	202 (52.7)	42 (11.0)	61 (15.9)	99 (25.8)
Greenhouse type
Vegetable greenhouses	2,168	1,407 (64.9)	761 (35.1)	6 (0.3)	306 (14.1)	449 (20.7)
Mushroom greenhouses	1,084	704 (64.9)	380 (35.1)	16 (1.5)	141 (13.0)	223 (20.6)
Flower greenhouses	1,355	879 (64.9)	476 (35.1)	12 (0.9)	186 (13.7)	278 (20.5)
Poultry greenhouses	813	528 (64.9)	285 (35.1)	8 (1.0)	110 (13.5)	167 (20.5)

Note:

a Data are given as numbers with percentages in parentheses.

Abbreviation: yr, year.

Table 2 The parameters of pulmonary function of responders by region, sex, age, and greenhouse type

Characteristics	Total (n)	Mean FEV1%	Mean FVC%	Mean FEV1/FVC%	FEV1/FVC <0.70 (%)	FEV1/FVC >0.70 but FEV^1 or FVC <80% (%)
Region
Plain	2,981	85.82	82.78	107.67	464 (15.6)a	1,156 (38.8)
Mountain area	1,220	83.26	80.12	106.79	246 (20.2)	561 (50.0)
Coastal area	1,219	82.52	80.51	106.32	237 (19.4)	556 (45.6)
Sex
Male	2,660	84.89	80.37	108.16	481 (18.1)	1,205 (45.3)
Female	2,760	84.13	82.93	106.21	466 (16.9)	1,068 (38.7)
Age (yr)
<40	1,732	88.50	85.42	107.01	7 (0.4)	441 (25.5)
40–49	1,734	84.95	81.42	108.38	214 (12.3)	775 (44.7)
50–59	1,571	82.75	79.84	107.38	500 (31.8)	789 (50.2)
≥60	383	71.61	73.42	101.54	226 (59.0)	128 (33.4)
Greenhouse type
Vegetable greenhouses	2,168	87.76	83.94	108.70	268 (12.4)	769 (35.5)
Mushroom greenhouses	1,084	82.18	79.74	105.97	266 (24.5)	530 (48.9)
Flower greenhouses	1,355	83.78	81.34	106.79	243 (17.9)	574 (42.4)
Poultry greenhouses	813	80.12	78.74	105.30	170 (20.91)	400 (49.20)

Notes: All responders received a bronchodilator and all the parameter values were postbronchodilator lung function.

a Data are given as numbers with percentages in parentheses.

Abbreviations: FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity; yr, year.

Table 3 Prevalence of COPD according to the Global Initiative for Chronic Obstructive Lung Disease diagnostic criteriaa by regions and greenhouse types in the Liaoning Province suburbs of the People’s Republic of China

	Plain	Mountain area	Coastal area	All areas	χ^2 value	P-valued
Vegetable greenhouses	11.3b	12.6	14.9	12.4
Mushroom greenhouses	21.4	29.3	27.5	24.5	77.75	<0.0005
Flower greenhouses	15.4	24.4	17.4	17.9	20.83	<0.0005
Poultry greenhouses	19.5	22.5	22.9	20.9	34.41	<0.0005
All greenhouses	15.6	20.2	19.4	17.5
χ^2 value		13.04	9.35
P-valuec		<0.0005	0.002

Notes:

a Postbronchodilator FEV₁/FVC <70% was defined as COPD according to the Global Initiative for Chronic Obstructive Lung Disease diagnostic criteria.

b Prevalence values are given as percentages.

c Comparing with the prevalence of COPD of subjects in plain area including all greenhouses.

d Comparing with the prevalence of COPD of subjects from all vegetable greenhouses in different regions.

Abbreviations: FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity.

Table 4 Stratification analysis of COPD prevalence in the Liaoning Province suburb of the People’s Republic of China by different physical features and greenhouse characteristics

	Responders (n)	COPD (n)	Prevalence (%)	χ^2 value	P-valuea
Sex				1.350	0.245
Male	2,660	481	18.1
Female	2,760	466	16.9
Age (yr)				1,110.921	<0.0005
<40	1,739	7	0.4
40–49	1,742	214	12.3
50–59	1,576	500	31.7
≥60	363	226	62.3
BMI (kg/m^2)				50.431	<0.0005
<18.5	73	34	46.6
18.5–23.9	2,013	373	18.5
24.0–27.9	2,686	448	16.7
≥28	648	92	14.2
Smoking status				70.756	<0.0005
Nonsmoker	3,505	500	14.3
Current smoker	1,915	447	23.3
Pack-years of smoking				6.969	0.031
0	3,505	500	14.3
1–14	55	21	38.2
15–29	743	170	22.9
≥30	1,117	256	22.9
Region				16.929	<0.0005
Plain	2,981	464	15.6
Mountain area	1,220	246	20.2
Coastal area	1,219	237	19.4
Greenhouse type				83.362	<0.0005
Vegetable greenhouses	2,167	268	12.4
Mushroom greenhouses	1,085	266	24.5
Flower greenhouses	1,355	243	17.9
Poultry greenhouses	813	170	20.9
Working years (yr)				44.601	<0.0005
<3	758	137	18.1
3–5	485	137	28.2
>5	4,177	673	16.1
Daily working hours in greenhouse (hr)				288.299	<0.0005
>3	604	211	34.9
3–5	2,162	488	22.6
>5	2,654	248	9.3
Plant area (m^2)				22.877	<0.0005
<1,000	2,325	471	20.3
1,000–2,000	1,243	181	14.6
>2,000	1,852	295	15.9
Heating materials in winter				9.323	0.025
Electricity	458	73	15.9
Coal	3,009	502	16.7
Mildewed grasses	1,167	206	17.7
None	786	166	21.1
Childhood greenhouse exposure				28.310	<0.0005
No	5,268	945	17.9
Yes	152	2	1.3
Asthma symptoms during childhood				5.745	0.017
No	5,393	947	17.6
Yes	27	0	0.0
Education				12.132	<0.0005
Primary school and below	1,633	330	20.2
Junior high school and above	3,787	617	16.3
Allergy history				5.092	0.024
No	5,173	917	17.7
Yes	247	30	12.1

Note:

a Univariate analysis of COPD prevalence for each variable.

Abbreviations: yr, year; BMI, body mass index; hr, hour.

Table 5 Risk factors for COPD among greenhouse farmers by multiple logistic regression analysis

Variables	OR	95% CI	P-value
Age (yr)
<40	Reference
40–49	64.93	26.52–158.99	<0.0005
50–59	252.70	102.80–621.20	<0.0005
≥60	528.12	209.92–998.65	<0.0005
BMI (kg/m^2)
<18.5	Reference
18.5–23.9	0.43	0.25–0.75	0.003
24.0–27.9	0.38	0.22–0.65	<0.0005
≥28	0.20	0.11–0.36	<0.0005
Smoking status
Nonsmoker	Reference
Current smoker	2.18	1.84–2.59	<0.0005
Pack-years of smoking (yr)
0	Reference
1–14	0.93	0.47–1.85	0.844
15–29	2.39	1.88–3.03	<0.0005
≥30	2.17	1.76–2.66	<0.0005
Region
Plain	Reference
Mountain area	1.68	1.37–2.06	<0.0005
Coastal area	1.35	1.10–1.65	0.003
Greenhouse type
Vegetable greenhouses	Reference
Mushroom greenhouses	1.46	1.13–1.87	0.004
Flower greenhouses	1.55	1.24–1.95	<0.0005
Poultry greenhouses	2.08	0.67–6.49	0.206
Working years (yr)
<3	Reference
3–5	1.52	1.08–2.15	0.017
>5	0.51	0.40–0.65	<0.0005
Daily working hours in greenhouse (hr)
<3	Reference
3–5	0.96	0.76–1.21	0.709
>5	1.09	0.83–1.43	0.548
Plant area (m^2)
<1,000	Reference
1,000–2,000	0.85	0.68–1.08	0.178
>2,000	0.91	0.73–1.12	0.358
Heating materials in winter
Electricity	Reference
Coal	1.13	0.83–1.53	0.456
Mildewed grasses	1.22	0.87–1.71	0.242
None	1.18	0.36–3.85	0.779
Childhood greenhouse exposure
Never	Reference
Ever	3.64	0.70–19.00	0.126
Asthma symptoms during childhood
No	Reference
Yes	0.68	0.08–5.62	0.716
Education
Junior high school and above	Reference
Primary school and below	1.11	0.94–1.33	0.229
Allergy history
No	Reference
Yes	0.99	0.64–1.54	0.98

Abbreviations: OR, odds ratio; CI, confidence interval; BMI, body mass index; yr, year; hr, hour.

Table S1 The categorization for variables

Variables	Categorization
Smoking status	0=Nonsmoking, 1=Current smoking
Childhood greenhouse exposure	0=Never, 1=Ever
Asthma symptoms during childhood	0=No, 1=Yes
Education	0=Junior high school and above, 1=Primary school and below
Allergy history	0=No, 1=Yes

Table S2 Categorical dummy variables coding

Variables	Dummy variables	Frequency	Parameter coding
			(1)	(2)	(3)
Age (yr)	<40	1,739	0	0	0
	40–49	1,742	1	0	0
	50–59	1,576	0	1	0
	≥60	363	0	0	1
BMI (kg/m^2)	<18.5	73	0	0	0
	18.5–23.9	2,013	1	0	1
	24–27.9	2,686	0	1	0
	≥28	648	0	0	1
Pack-years of smoking	0	3,505	0	0	0
	1–14	55	1	0	1
	15–29	743	0	1	0
	≥30	1,117	0	0	1
Region	Plain	2,981	0	0
	Mountain area	1,220	1	0
	Coastal area	1,219	0	1
Greenhouse type	Vegetable greenhouses	2,167	0	0	0
	Poultry greenhouses	813	1	0	0
	Mushroom greenhouses	1,085	0	1	0
	Flower greenhouses	1,355	0	0	1
Working years (yr)	<3	758	0	0
	3–5	485	1	0
	>5	4,177	0	1
Daily working hours in greenhouse (hr)	<3	604	0	0
	3–5	2,162	1	0
	>5	2,654	0	1
Plant area (m^2)	<1,000	2,325	0	0
	1,000–2,000	1,243	1	0
	>2,000	1,852	0	1
Heating materials in winter	Electricity	458	0	0	0
	Coal	3,009	1	0	0
	Mildewed grasses	1,167	0	1	0
	None	786	0	0	1

Abbreviations: yr, year; BMI, body mass index; hr, hour.

Table S3 Prevalence of COPD according to the Global Initiative for Chronic Obstructive Lung Disease diagnostic criteria by sex and smoking status in the Liaoning Province of the People’s Republic of China

	Nonsmoker	Current smoker	χ^2 value	P-value	All	χ^2 value	P-value
Male	12.5g	23.3	36.271a	<0.0005a	18.1
Female	15.8	21.6	7.114b	0.008b	16.9
χ^2 value	5.202c	0.395d				0.948f	0.333f
P-value	0.023c	0.530d
All	14.3	22.8
χ^2 value			48.671e
P-value			<0.0005e

Notes:

a Comparison of the COPD prevalence among male greenhouse farmers between nonsmokers and current smokers.

b Comparison of the COPD prevalence among female greenhouse farmers between nonsmokers and current smokers.

c Comparison of the COPD prevalence among nonsmokers between male and female.

d Comparison of the COPD prevalence among current smokers between male and female.

e Comparison of the COPD prevalence between nonsmokers and current smokers.

f Comparison of the COPD prevalence between male and female.

g Prevalence values are given as percentages.