Environmental pollution contributes differentially to health hazards in different populations, in which children belong to typical susceptible groups. Compared with adults, children have a large amount of activity, a fast breathing rate, and rapid development of body structure and organs. Their respiratory, immune, and other systems are not well developed, and they are more sensitive to harmful substances in the environment.1 Studies have shown that the indoor environment, renovation of dwellings, dampness inside dwellings, heating and ventilation of buildings, indoor air quality, and life habits of households are related to preschool child health.2,3 Otitis is an inflammation of the ear. It is usually divided into two types (otitis externa and otitis media) and is an infectious disease secondary to the common cold in children.4 Presently, studies on otitis in preschool children have focused on the effects of medication, and there are few investigations on the indoor environmental factors associated with the occurrence of otitis in preschool children. Concurrently, children's hearing organs and brains were irreversibly injured due to the lack of attention paid by parents to the prevention of acute otitis attacks. Therefore, it is necessary to extensively study the health effects of indoor environmental pollution on preschool children in China. This study was conducted from April to August 2019 and investigated residential environmental and otitis risk factors of preschool children in 60 kindergartens in Urumqi. This study aimed to explore the potential risk factors affecting the occurrence of otitis in preschool children and provide corresponding measures for the prevention of such diseases.

Otitis in children is mainly caused by bacteria, of which 69.7% are gram-positive bacteria, 16.7% are gram-negative bacteria, and 13.6% are fungi.7 Presently, China's medical treatment places otitis under the category of the five organ diseases, so some pediatricians have a vague understanding of it, which leads to a missed diagnosis by physicians, thus concluding that the prevalence of otitis in Chinese children is low and not paid attention to. However, according to the results of this survey, the prevalence of otitis in preschool children in Urumqi was 13.1%, which was higher than the prevalence (11.9%) of otitis among 4618 children in Urumqi investigated by Wang8 in 2013. This further suggests that more attention should be paid to the prevalence of otitis in preschool children. At the onset of otitis, a vast majority of physicians provide antibiotic therapy. In a study by Trinh et al.,9 the antibiotic prescription rate for otitis was 68–80 per 100 visits. Several international guidelines recommend antibiotics for children aged < 2 years with acute otitis media. However, in older children, only cases of high fever and severe ear pain require antibiotics. Overuse and inappropriate use of antibiotics are the main reasons for the emergence of antibiotic resistance.10,11 Among them, aminoglycoside antibiotics, such as streptomycin and gentamicin, have good efficacy against diseases caused by bacteria. However, its prolonged use causes its accumulation in the inner ear lymph nodes, causing the death of hair cells in the inner ear and irreversible ototoxic effects.12 The results of the present study also showed that the prevalence of otitis was 6.6% higher in children who had been treated with antibiotics than in those who had not. It was speculated that the non-standard use or abuse of antibiotics in the early years changed the susceptibility of pathogenic otitis bacteria to antibiotics, resulting in lower resistance and higher prevalence of otitis in preschool children.

The impact of the indoor environment on human health has gained much attention from the international community,13–15 especially for preschool children whose various organs and systems of the body are not yet developmentally mature. With the increase in living standards of the Chinese residents, there is also an increasing variety of furniture and new synthetic materials in dwellings, with a consequent exposure problem of chemical components. Shin et al.16 showed that formaldehyde can enter the body through the skin and eye contact, inducing the expression of inflammatory factors and mucins in human ear epithelial cells, thereby increasing the probability of developing otitis in children. Formaldehyde in residential environments mainly originates from decorating with artificial sheets, furniture, cellophane, and various types of wall materials. The results of the present study similarly showed that the purchase of new furniture and renovation in the mother's home before pregnancy and the purchase of new furniture and renovation in the homes of children at the age of 0–1 year were both associated with the development of otitis in preschool children. Concurrently, summer in Urumqi, Xinjiang, has long promoted a high-temperature environment, and the indoor temperature increases, as does the rate of formaldehyde release. A high-temperature environment is more conducive to the breeding and reproduction of fungi, which further expands the exposure risk of preschool children. Indoor decorative materials have been repeatedly associated with the occurrence of respiratory diseases in children.2,17,18 The results of this study showed that floor material, wall surface material, and carpet placement in a room were associated with otitis occurrence in children. It is presumed that newly purchased furniture and renovation materials in dwellings have some volatilization of chemical composition. Prolonged environmental exposure leads to impairment of the respiratory and immune systems of children, who are more susceptible to invasive bacterial infections that induce otitis.

Several review studies19,20 have shown that exposure to mold and dampness in the home residential environment is an important indoor environmental risk factor. Dampness in dwellings promotes the breeding of indoor microbes, of which bacteria and mold are the most common. Bacteria can affect the child's immune system, and molds can be harmful to human health by suspending them in the air. Prolonged indoor dampness also leads to heavy multiplication of dust mites, which in turn triggers disease reactions, such as allergic rhinitis, in children.21 Moreover, pests raised in damp dwellings, such as mice and cockroaches, carry pathogenic bacteria. Preschool children have a stronger desire to explore the world spirit, and a larger range of indoor activities, and have greater exposure to these causative factors than adults who remain indoors for longer periods. However, the results of the present study found that dampness in the home before versus during pregnancy of mothers was not a risk factor for the development of otitis media in preschool children.

This study has some limitations. Because this study did not consider risk factors for outdoor and child exposure in preschool and used a cross-sectional survey with poor causal ability, the results may have been biased. Otitis includes otitis externa and otitis media, which are further divided into acute and chronic otitis media. As defined above, one of these phenomena and the occurrence of otitis were considered. Therefore, the calculated prevalence of otitis in this study was higher than that in any of the abovementioned studies. Elucidation of specific risk factors for the development of otitis in preschool children should be confirmed by population-based cohort studies to allow further observation of environmental and developmental relationships with disease development in childhood.

The prevalence of otitis in preschool children is high, and it has a certain association with indoor environmental factors. Residence renovation, tide, and humidity during pregnancy are all risk factors for the development of otitis in preschool children. The diagnosis of otitis in children should be added to the consideration of environmental factors when they come to relevant units such as hospitals, and parents should also pay attention to the indoor living environment. Reduction of indoor renovation of the dwellings of children during their growth and development and regular vector abatement of the dwellings actively improve children's indoor living environments, thereby effectively preventing otitis in preschool children.

The datasets generated and/or analyzed during the current study are not publicly available due to the data belonging to the School of Public Health of Fudan University but are available from the corresponding author upon reasonable request.

This study was supported by the National Natural Science Foundation of China (grant no. 81660140, 81860179); Teacher's professional development project of the Shanghai Municipal Education Commission and High-Level Local University Construction Projects of Shanghai University of Medicine & Health Sciences; The Key Discipline of the 14th 5-Year Plan in Xinjiang Uygur Autonomous Region-Public Health and Preventive Medicine.