Fractional exhaled nitric oxide (FeNO) and respiratory symptoms in junior high school students in Penang, Malaysia: the role of household exposure

Figures & data

Table 1. Demographics and home environment of the students in Penang (N = 348).

	N	Prevalence (%)
Demographic variables
Girl (%)	184	52.9
Current smoker (%)	10	2.9
Malay	245	70.4
Chinese	48	13.8
Indian	55	15.8
Home environment variables
Apartment	153	44.0
Wooden house	71	21.1
Cat keeping	70	20.1
Dog keeping	24	6.9
Keeping birds	11	3.2
ETS at home	167	48.3
Any dampness or mould last 12 months^a	122	35.1
Any dampness, water leakage or mould last 5 years	72	21.1
Any dampness, water damage or mould last 12 months or last 5 years	157	45.1
Indoor painting last 12 months	146	43.2
New floor materials last 12 months	42	12.4

^aFlooding or water leakage, floor dampness, indoor mould or mould odour.

Table 2. Bivariate associations between FeNO and health variables (N = 348)^a.

Type of health variable	Prevalence (%)	Yes (N)	FeNO GM (GSD)	No (N)	FeNO GM (GSD)	p-value^a
Ever had asthma	13.2	46	33.4 (2.51)	302	18.4 (2.29)	<0.001
Doctor’s diagnosed asthma	10.6	37	32.4 (2.50)	311	18.8 (2.31)	<0.001
Wheeze in the last 12 months	14.1	49	28.9 (2.44)	298	18.8 (2.32)	0.001
Any daytime breathlessness (rest or exercise) last 12 months	38.0	130	20.8 (2.44)	218	19.4 (2.32)	0.448
Nocturnal attacks of shortness of breath last 12 months	10.8	37	18.7 (2.29)	305	20.1 (2.38)	0.631
Current asthma	7.8	27	30.5 (2.92)	320	19.1 (2.29)	0.007
Weekly eye symptoms last 3 months	18.0	62	28.4 (2.55)	282	18.3 (2.28)	<0.001
Weekly nose symptoms last 3 months (rhinitis)	31.4	108	24.9 (2.45)	236	18.1 (2.29)	0.001
Pollen allergy	8.6	30	24.9 (2.45)	318	19.5 (2.36)	0.135
Cat allergy	8.3	29	31.0 (2.43)	319	19.1 (2.34)	0.004
Dog allergy	3.2	11	23.1 (2.57)	337	19.9 (2.37)	0.561
Mould allergy	5.2	18	21.8 (2.78)	330	19.9 (2.35)	0.650
Seafood allergy	14.1	49	27.9 (2.54)	299	18.9 (2.31)	0.003
Parental asthma/allergy (heredity)	24.1	84	23.1 (2.45)	264	19.0 (2.50)	0.069
Respiratory infection last 7 days	27.3	95	24.9 (2.25)	253	18.3 (2.38)	0.003

^aTested by Students t-test for log-transformed FeNO values.

Significance for bold values is p < 0.05.

Table 3. Two-level linear mixed models (classroom, student) on associations between selected health variables and FeNO^a (N = 348).

Health variables	FeNO antilog-beta (95%CI)	p-value
Doctor’s diagnosed asthma	1.65 (1.23–2.19)	0.001
Current wheeze	1.53 (1.18–1.97)	0.001
Current asthma	1.71 (1.22–2.40)	0.002
Weekly eye symptoms	1.46 (1.15–1.83)	0.002
Weekly nose symptoms (rhinitis)	1.36 (1.12–1.65)	0.002
Pollen allergy	1.26 (0.92–1.73)	0.157
Cat allergy	1.51 (1.09–2.09)	0.009
Seafood allergy	1.58 (1.23–2.04)	<0.001
Parental asthma/allergy	1.24 (1.00–1.53)	0.047
Respiratory infections last 7 days	1.31 (1.07–1.60)	0.008

^aAdjustment for, ethnicity, gender, smoking and ETS at home (one health variable per model). Models were created for health variables with p < 0.2 in the crude analysis.

Significance for bold values is p < 0.05.

Table 4. Two-level (classroom, student) multiple logistic regression analysis of associations between selected health variables (dependent variables) and categorized FeNO levels (N = 348).

Dependent variable	Doctor diagnosed asthma	Wheeze	Current asthma	Weekly ocular symptoms	Weekly nasal symptoms (rhinitis)	Respiratory infection last 7 days
Categorized FeNO variable	OR (95% CI)	OR (95% CI)	OR (95% CI)	OR (95%CI)	OR (95% CI)	OR (95% CI)
Normal (<20 ppb)	1 (ref)	1 (ref)	1 (ref)	1 (ref)	1 (ref)	1 (ref)
Intermediate (20–35 ppb)	1.72 (0.64–4.56) (p = 0.287)	3.00 (1.33–6.75) (p = 0.008)	1.02 (0.30–3.45) (p = 0.983)	0.81 (0.35–1.87) (p = 0.617)	1.12 (0.61–2.05) (p = 0.389)	2.18 (1.15–4.12) (p = 0.023)
High (>35 ppb)	2.68 (1.15–6.22) (p = 0.022)	4.26 (1.97–9.18) (p <0.001)	2.77 (1.08–7.13) (p = 0.035)	2.26 (1.25–3.81) (p = 0.013)	2.18 (1.25–3.81) (p = 0.006)	3.13 (1.67–5.86) (p < 0.001)

Keeping gender, ethnicity, current smoking, ETS at home, reported allergy (pollen, cat or seafood allergy) and categorized FeNO in all models (one model per health variable).

Significance for bold values is p < 0.05.

Table 5. Associations between selected home environment variables (>20% prevalence) and current wheeze, ocular symptoms, rhinitis and respiratory infections (N = 620).

Home environment variable	Wheeze OR (95% CI)	p-value	Ocular symptoms OR (95% CI)	p-value	Rhinitis OR (95% CI)	p-value	Respiratory infection OR (95% CI)	p-value
Apartment building	0.78 (0.45–1.36)	0.377	1.35 (0.83–2.20)	0.225	0.76 (0.51–1.14)	0.186	0.83 (0.49–1.41)	0.495
Wooden house	1.58 (0.90–2.58)	0.114	0.77 (0.45–1.31)	0.335	1.11 (0.73–1.69)	0.617	1.16 (0.62–2.20)	0.641
ETS at home	1.19 (0.71–1.99)	0.513	0.95 (0.59–1.55)	0.850	1.14 (0.78–1.67)	0.505	1.06 (0.64–1.77)	0.813
Cat keeping	1.01 (0.55-1.86)	0.972	0.92 (0.52–1.64)	0.784	1.57 (1.02–2.43)	0.041	2.29 (1.24–4.25)	0.008
Any dampness, water leakage or mould^a	1.72 (1.03–2.87)	0.038	1.03 (0.63–1.66)	0.916	1.18 (0.81–1.73)	0.383	1.47 (0.89–2.43)	0.129
Indoor painting last 12 months	0.84 (0.50–1.41)	0.501	0.88 (0.54–1.42)	0.596	1.13 (0.77–1.64)	0.542	0.95 (0.56–1.60)	0.839

Associations analysed by two-level (classroom, student) multilevel logistic regression models, keeping gender, ethnicity, current smoking, parental asthma/allergy reported allergy (pollen or cat or seafood allergy) in all models

^aWater leakage or flooding, signs of floor dampness, visible indoor mould or mould odour in the last 12 months and/or water leakage, dampness or mould in the last 5 years

Significance for bold values is p < 0.05.

Table 6. Stratified analysis of associations between selected home environment variables and current wheeze, rhinitis and respiratory infections by two-level (classroom, student) multilevel logistic regression^a.

	Stratification variable groups	Wheeze OR (95% CI)	Interaction p-value	Rhinitis OR (95% CI)	Interaction p-value	Current respiratory infections OR (95% CI)	Interaction p-value
Home exposure variable
Cats at home	Normal FeNO	3.46 (0.64–18.6) p = 0.148	0.026	2.32 (0.98–5.52) p = 0.056	0.945	2.75 (1.08–7.03) p = 0.034	0.769
Cats at home	Elevated FeNO	0.51 (0.14–1.78) p = 0.290		1.62 (0.63–4.18) p = 0.322		2.44 (0.90–6.65) p = 0.081
Home exposure variable
Dampness/mould^b	Normal FeNO	2.11 (0.60–7.36) p = 0.242	0.634	1.22 (0.60–2.46) p = 0.584	0.476	1.21 (0.55–2.63) p = 0.638	0.171
Dampness/mould^b	Elevated FeNO	3.44 (1.43–8.27) p = 0.006		1.71 (0.78–3.75) p = 0.183		2.48 (1.11–5.53) p = 0.026
Home exposure variable
Dampness/mould^b	Concrete construction	0.91 (0.46–1.80) p = 0.796	0.042	1.21 (0.74–1.99) p = 0.441	0.416	1.22 (0.68–2.20) p = 0.498	0.088
Dampness/mould^b	Wooden construction	5.54 (2.10–14.6) p = 0.001		1.04 (0.54–1.99) p = 0.911		2.96 (0.94–9.32) p = 0.064
Home exposure variable
Dampness/mould^b	No cats at home	1.62 (0.89–2.94)¨ p = 0.112	0.467	1.11 (0.71–1.75) p = 0.64	0.658	1.67 (0.94–2.97) p = 0.08	0.541
Dampness/mould^b	Cats at home	4.01 (0.98–16.4) p = 0.053		1.32 (0.63–2.77) p = 0.46		1.06 (0.36–3.15) p = 0.91

^aAdjusting for gender, ethnicity, current smoking, parental asthma/allergy reported allergy (pollen or cat or seafood allergy) in all models.

^bWater leakage or flooding, signs of floor dampness, visible indoor mould or mould odour in the last 12 months and/or water leakage, dampness or mould in the last 5 years

Significance for bold values is p < 0.05 for association p-values and p < 0.1 for interaction p-values.