Table 1.

Characteristics of the included studies

Author, year	Region	Study period	Number of samples	Age	Type of respiratory allergy	Urban/rural classification	Definition of disease	Adjusted variables	Quality assessment
Akmatov M.K., 2020 [8]	Germany	2009–2016	Urban: 32,400,372 Rural: 14,028,047	All ages	Asthma	Urban: Germany’s 16 federal states included 106 administrative districts in 2011 Rural: Germany’s 16 federal states included 296 administrative districts in 2011	ICD-10-GM, code J45	Not specified	Good
Levin M.E., 2020 [18]	South Africa	Not specified	Urban: 1185 Rural: 398	12–36 months	Asthma, AR	Urban: Cape Town Rural: Eastern Cape province	Modified ISSAC criteria	No adjustment	Poor
Norbäck D., 2018 [19]	China	2005–2012	Urban: 29,262 Rural: 1520	3–6 years	Asthma	Not specified	Yes/no question asking if the child had ever been diagnosed by a doctor	All personal factors (sex, age, birth season, birth weight, breastfeeding, parental atopy), all indoor factors (lifetime passive smoking, lifetime mold/dampness) and outdoor factors (living near traffic, lifetime outdoor T, lifetime outdoor NO2), and socioeconomic status (SES) factors (maternal occupation during pregnancy, home size, number of persons living in the current home, current residential area, and GDP per capita)	Poor
Lavin T., 2017 [32]	India, Vietnam	2002–2016	Urban: 833 Rural: 2969	7.5–8.5 years	Asthma	Several factors are considered by two reports to assess whether a community/environment type reflects a rural or urban environment, including agriculture and industry, and environment and services	Face-to face interviews if the child had long-term respiratory problems such as asthma (may include clinical diagnosis or hospital admission)	No adjustment	Poor
Dostál M., 2014 [33]	Czech Republic	1994–1999	Urban: 466 Rural: 455	0–10 years	AR	Urban: the Teplice district—can produce highly concentrated pollutants from both local and remote sources Rural: the less polluted rural district of Prachatice	ICD-10 codes	Sex, low birth weight (< 2500 g) and/or gestation < 37 weeks, maternal education, maternal allergy, an older sibling with allergy, and breastfeeding	Good
Lawson J.A., 2014 [34]	Canada	1994–2007	Urban: 1,649,462 Rural: 389,428	12–18 years	Asthma	Areas with a population of fewer than 1000 people or with a population density of <400 people/km2 were considered rural based on Canadian Census Rural Areas which accounts for population size and density	Has [NAME] ever had asthma that has been diagnosed by a health professional?	Sex, age, income, body mass index, passive smoking exposure, personal smoking, physical exercise	Good
Stoner A.M., 2013 [11]	USA	2002–2006	Urban: 5800 Rural: 1100	5.5 years	Asthma	Not specified	Since your child turned (x) years of age, has a doctor, nurse, or other medical professional ever told you that your child has asthma?	No adjustment	Good
Valet R.S., 2011 [35]	USA	1995–2000	Urban: 52,168 Rural: 38,317	0–5.5 years	Asthma, AR	Urban: central county within 1 of Tennessee’s 4 standard metropolitan statistical areas Rural: county outside a standard metropolitan statistical areas	ICD-9 codes	Birth weight, sex, race, chronic medical conditions, history of bronchiolitis, maternal smoking, maternal education, and maternal history of asthma	Good
Midodzi W.K., 2010 [7]	Canada	1996–2003	Urban: 5823 Rural: 2602	<2 years	Asthma	Urban: central metropolitan area Rural: non-central metropolitan area	Physician-diagnosed	Sex, birth weight, breastfeeding, history of early wheezing, history of childhood allergy, history of nose/throat infection, early daycare attendance, single parent household, maternal medication use in pregnancy, maternal smoking during pregnancy, number of older siblings present at birth, household socio-economic index, and geographic regions	Poor
Midodzi W.K., 2007 [36]	Canada	1994–1997	Urban: 10,945 Rural: 2570	0–11 years	Asthma	Not specified	Physician-diagnosed	Age, sex, child allergies, no. of pediatrician visits, no. of physician visits, mothers’ age at child’s birth, older sibling, parental history of asthma, immigrant mother, either parent smoked, home needing repairs, geographic region, body mass index, socioeconomic status, and crowding index	Poor
Priftis K.N., 2007 [37]	Greece	1995–2004	Urban: 446 Rural: 312	8–10 years	Asthma	Urban: municipality of Maroussi characterized by the air pollution with heavy traffic Rural: Aliartos and another three adjoining agricultural villages 5 km around the station monitoring air quality in the area	The questionnaire included the ISAAC core questions on symptoms of asthma, physician-diagnosed asthma	No adjustment	Poor
Bråbäck L., 2004 [38]	Sweden	1952–1981	Urban:1,119,437 Rural: 197,548	17–20 years	Asthma, AR	Urban is defined as a home located in a settlement with at least 200 inhabitants.	ICD-8, 9, and 10 codes	County of residence, urban/rural living, family size, overcrowding, being the first-born boy, and maternal age at the birth of the child	Good
Dik N., 2004 [39]	Canada	1980–1990	Urban: 76,472 Rural: 81,118	0–6 years	Asthma	Urban: metropolitan Winnipeg—approximately 650,000 or 54% of the total provincial population Rural: outside Winnipeg—the largest town having 30,000 people	ICD-493	Sex, primary care	Good
Shima M., 2003 [12]	Japan	1990–1997	Urban: 1020 Rural: 838	6–9 years	Asthma	Urban: six schools in four communities (Chiba, Funabashi, Kashiwa, and Ichikawa) Rural: four schools in four communities (Ichihara, Tateyama, Mobara, and Kisarazu)	Two or more episodes of wheezing accompanied by dyspnea that had ever been given the diagnosis of asthma by a physician and the occurrence of asthmatic attacks or the need for any medication for asthma during the past 2 years	Sex, school grade, history of allergic diseases, respiratory diseases before 2 years of age, breastfeeding in infancy, parental history of allergic diseases, maternal smoking habits, house of steel or reinforced concrete, use of unvented heater in winter	Good

AR allergic rhinitis, ISAAC International Study of Asthma and Allergies in Children