Urban–Rural Differences in the Epidemiology of Asthma and Allergies in Nigeria: A Population-Based Study

Figures & data

Figure 1 Sampling approach for participant selection.

Table 1 General Characteristics of the Subjects

Characteristics	Urban N=635	Rural N=275	Total N=910	p values
Mean (yr) Age ± Std	31±12	38±16	33±13	<0.001
Sex
Male	266 (41.9)	100 (36.4)	366 (40.2)	0.118
Female	369 (58.1)	175 (63.6)	544 (59.8)
Educational level
No formal	27 (4.3)	44 (16.0)	71 (7.8)	<0.001
Primary	82 (12.9)	82 (29.9)	164 (18.0)
Secondary	200 (31.5)	103 (37.5)	303 (33.3)
Tertiary	326 (51.3)	46 (16.7)	372 (40.9)
Marital Status
Married	313 (49.3)	171 (62.2)	484 (53.2)	<0.001
Single/divorced	322 (50.7)	104 (37.8)	416 (46.8)
Tribe
Yoruba	544 (85.7)	197 (71.6)	741 (81.4)	<0.001
Hausa	19 (3.0)	45 (16.4)	64 (7.0)
Igbo	16 (2.5)	5 (1.8)	21 (2.3)
Others	56 (8.8)	28 (10.2)	844 (9.2)
Multi-allergy
One	180 (28.3)	93 (33.8)	273 (52.3)	0.030
Two	96 (15.1)	52 (18.9)	148 (16.3)
Three	12 (1.9)	1 (0.4)	13 (1.4)
Ever asthma	39 (6.1)	8 (2.9)	45 (5.2)	0.043
Ever nasal allergy	162 (25.5)	103 (37.5)	265 (29.1)	<0.001
Ever skin allergy (eczema)	131 (20.6)	73 (26.5)	204 (22.4)	0.049
Physician diagnosed asthma	31 (4.9)	8 (2.9)	39 (2.3)	0.177
Physician diagnosed allergic rhinoconjunctivitis	46 (7.2)	19 (6.9)	65 (7.1)	0.857
Physician diagnosed skin allergy (eczema)	43 (6.8)	28 (10.2)	71 (7.8)	0.078
Cigarette smoking	38 (6.0)	28 (10.2)	66 (7.3)	0.025
Parental smoking	53 (8.3)	30 (10.5)	83 (9.1)	0.218
Use of alcohol	51 (8.1)	32 (11.6)	83 (9.1)	0.085

Note: Results are expressed in number and % in parentheses.

Table 2 Age-Adjusted Prevalence of Allergic Disorders by Sites

Characteristics	Urban N=635	Rural N=275	Total N=910	p values
Possible asthma	11.7 (9.2–14.2)	10.2 (6.6–13.7)	12.7 (10.5–14.9)	0.511
WHO clinical asthma	4.0 (2.0–4.7)	1.5 (0.7–3.0)	3.8 (2.5–5.1)	0.050
ECRHS asthma definition	3.4 (2.5–5.5)	0.5 (0–1.4)	2.9 (1.8–3.9)	0.011
Current allergic rhinoconjunctivitis	26.2 (22.7–29.6)	22.2 (17.3–27.1)	28.4 (25.5–31.3)	0.201
Current skin allergy (eczema)	13.9 (11.2–16.6)	10.5 (6.9–14.2)	14.5 (12.2–16.8)	0.160
Physician diagnosed asthma	3.3 (1.9–4.6)	1.5 (0.7–3.0)	3.7 (2.5–4.9)	0.128
Physician diagnosed allergic rhinoconjunctivitis	4.9 (3.2–6.6)	3.2 (1.1–5.3)	5.0 (3.6–6.4)	0.250
Physician diagnosed skin allergy (eczema)	4.8 (3.2–6.5)	4.6 (2.1–7.0)	5.4 (3.9–6.9)	0.896

Notes: Results are expressed in adjusted odd ratio with 95% CI in parentheses. ECRHS asthma definition: reporting a previous asthma attack or currently taking asthma medication within the preceding 12 months. Possible asthma: reporting shortness of breath or asthma attack in the preceding 12 months or currently taking asthma medication. ISACC Current allergic rhinoconjunctivitis: reporting sneezing or a runny or blocked nose in the absence of a cold accompanied by itchy watery eyes in the past 12 months. ISACC Current skin allergy (eczema): reporting rash at any time in the past 12 months and has affected any of the following places: the folds of the elbows; behind the knees; in front of the ankles; under the buttocks; or around the neck, ears, or eyes.

Table 3 Age-Adjusted Prevalence of Allergic Disorders by Site and Sex

Age group (in years)	Asthma urban	Asthma rural	AR urban	AR rural	Skin allergy urban	Skin allergy rural
18–19	1.4	–	9.9	–	5.2	–
20–29	0.8	0.2	6.4	8.9	4.2	5.3
30–39	0.3	–	4.4	4.8	2.0	2.1
40–49	0.3	0.2	3.1	3.2	1.5	0.9
50–59	0.1	0.2	1.9	3.0	1.0	1.2
60–69	0.1	–	0.5	0.7	0.1	0.5
70–79	–	–	–	0.9	–	–
80+	–	–	–	0.7	–	0.7
Sex
Male	2.5	1.0	19.3	24.8	10.0	9.9
Female	2.6	1.7	18.4	22.9	10.7	13.1

Note: Results are expressed in %.

Abbreviations: AR, Allergic Rhinitis.

Table 4 Age-Adjusted Prevalence of Asthma and Respiratory Symptoms by Site

Asthma and respiratory symptoms	Urban N= 635	Rural N=275	Total N=910	P values
Wheezing in last 12 months	10.1 (7.8–12.4)	7.8 (4.6–10.9)	10.8 (8.8–12.8)	0.275
Woken by SOB in last 12 months	10.7 (8.3–13.1)	10.0 (6.5–13.5)	11.8 (9.7–13.9)	0.787
Woken by cough in last 12 months	13.4 (10.8–16.1)	13.6 (9.5–17.7)	14.7 (12.4–17.0)	0.935
Woken by chest tightness in last 12 months	9.6 (7.3–11.9)	7.6 (4.5–10.8)	10.1 (8.2–12.1)	0.333
Asthma attack in last 12 months	2.5 (1.3–3.7)	0.5 (0–1.4)	2.1 (1.2–3.0)	0.042
Current asthma medication	2.7 (1.4–3.9)	0.5 (0–1.4)	2.3 (1.3–3.3)	0.031
Current nasal allergy	26.2 (22.7–29.6)	22.2 (17.3–27.1)	28.4 (25.5–31.3)	0.201

Notes: Results are expressed in adjusted odd ratio with 95% CI in parentheses. Current nasal allergy – Do you have any nasal allergies?

Figure 2 Asthma/allergic respiratory symptoms triggers.

Table 5 Association between Urbanization and Allergic Disease

Residence of subjects	Asthma	Allergic rhinitis	Skin allergy
Residing in urban areas	5.6 (1.9-19.6)	1.7 (1.2–2.4)	1.01 (0.7–1.8)
Residing in rural areas	1	1	1

Notes: Results are expressed in adjusted odd ratio with 95% CI after adjusting for cofounders. Asthma was defined by ECRHS asthma definition. AR and skin allergy was defined as Ever AR and EC, respectively.