Relative Humidity Affects Acute Otitis Media Visits of Preschool Children to the Emergency Department

Abstract

Objective:

The associations between climate variables and diseases such as respiratory infections, influenza, pediatric seizure, and gastroenteritis have been long appreciated. Infection is the main reason for acute otitis media (AOM) incidence. However, few previous studies explored the correlation between climatic parameters and AOM infections. The most important meteorological factors, temperature, relative humidity, and fine particulate matter (PM2.5), were included in this study. We studied the relationship between these meteorological factors and the AOM visits.

Materials and Methods:

It was a retrospective cross-sectional study. A linear correlation and a linear regression model were used to explore the AOM visits and meteorological factors.

Results:

A total of 7075 emergency department visits for AOM were identified. Relative humidity was found an independent risk factor for the AOM visits in preschool children (regression coefficient = −10.841<0, P = .039 < .05), but not in infants and school-age children. Average temperature and PM2.5 were not correlated with AOM visits.

Conclusion:

Humidity may have a significant inverse impact on the incidence of AOM in preschool-age children.

Keywords

acute otitis media humidity pediatric preschool meteorological factors

Introduction

Acute otitis media (AOM) is a middle ear infection among children during the winter season.^1

-4 It has risen to become one of the most common infections for pediatric consultations to ENT doctors.¹ An estimated 80% of children have at least one episode of AOM.¹

Studies revealed an association between climate changes and incidence of human illness,^5
-7 including respiratory tract infections,^6,8,9 influenza,^10,11 pediatric seizure,¹² and gastroenteritis.¹³ In the early 20th century, an epidemiological study from the Netherlands demonstrated that upper respiratory tract infections increased as outdoor temperature decreased.¹⁴ Recently, more and more experimental and epidemiological studies have shown that low temperature and dry air, either separately or combined, increase the risk of viral respiratory infections.^9,11,15

-18 Besides, exposure to particulate matter (PM_2.5) adversely affected human health impacts, such as asthma symptoms.¹⁹ The associations between climate variables and respiratory infections have been long appreciated.^{8,9,15,17,20
-22} However, no previous studies explored the associations between climatic parameters and AOM infections.

In this study, we focused on examining the effects of climate conditions such as temperature, relative humidity (RH), and PM_2.5 on the number of AOM-related emergency department visits. We sought to determine whether meteorological variables would impact the pediatric AOM incidence in Shanghai.

Materials and Methods

Study Setting

This study was performed at the ENT emergency department of Shanghai Eye, Ear, Nose, and Throat Hospital in China. The hospital is one of the most famous hospitals and ranked top in the major of otorhinolaryngology in China. It is also the largest specialized ENT hospital in Shanghai, which provides medical care for about 200 ENT emergency cases daily. We retrospectively analyzed pediatric patients’ medical records younger than 12 years who visited the emergency department for AOM from January 1, 2014, to July 31, 2015. We collected data from the medical records as follows: gender, patient age, arrival date, arrival time, and diagnosis. The inclusion criteria in the study were (1) age 0 to 12 years old; (2) diagnosed as AOM; and (3) first onset during one episode. Signs and symptoms of AOM included otalgia and tugging, rubbing, or holding of the ear. Examination revealed an inflamed, bulging drum with reduced mobility.¹ The institutional ethics committee approved the study protocols of our hospital (approved number: 2015038).

Meteorological Data and Variable Grouping

Values of mean monthly weather parameters for the period of analysis were obtained from the National Climate Data Service System, including average temperature(°C), RH (%), and fine PM2.5 (μg/m³). The RH is defined as the relative proportion of water in the air compared to the maximum water vapor. Particulate matter was defined as PM2.5 equal to two and one-half microns or less in width. Particulate matter2.5 was used to assess environmental pollutant effects in this study. The associations between the above meteorological factors and the AOM-related emergency department visits were explored in terms of monthly value because of the lag effects of weather conditions and the progress of AOM. Shanghai is characterized by an evident annual seasonal pattern of weather conditions, dry winter, and humid summer. The age was divided into 3 groups: 0 to 3 years old (infant), 4 to 6 years old (preschool children), and 7 to 12 years old (school children).

Statistical Analyses

Normally distributed continuous data are presented as mean ± SD. Categorical variables were compared with the χ² test. Enumeration data were analyzed by the goodness-of-fit test (χ²). The effect of meteorological factors on the number of AOM-related emergency department visits was analyzed by Pearson correlation analysis. Whether the meteorological data can affect AOM patients’ visits in the different age groups was analyzed by linear regression analysis. Statistical significance was set at P < .05. All statistical analysis was performed using SPSS22.

Results

Demographic Characteristics of AOM Patients Younger Than 12 Years

Table 1 showed a summary of the demographics of the study population. During the study time from January 1, 2014, to July 31, 2015, there were a total of 7075 AOM visits aged younger than 12 years at Shanghai Eye, Ear, Nose, and Throat Hospital. During this period, the resident population in Shanghai was approximately 24 million. The visits varied in the 4 seasons (P < .001), and males were more affected than females (P < .001). The rate peaked in the preschool-age group (P < .001).

Table 1.

Demographic Characteristics of AOM-Related ER Visits Younger Than 12 Years in Shanghai, From January 2014 to July 2015.

Variables		Numbers	Percentage (%)	χ²	P value
Gender	Male	3893	55.02	71.45	<.001
Gender	Female	3182	44.98
Age group	From 0 to 3 years old	1464	20.7	638.711	<.001
Age group	From 4 to 6 years old	3197	45.2
	From 7 to 12 years old	2414	34.1
Visits in varied seasons	Spring (from March to May)	1921	27.15	272.57	<.001
	Summer (from June to August)	1290	18.23
	Fall (from September to November)	1635	23.11
	Winter (from December to February)	2229	31.51

Abbreviation: AOM, acute otitis media.

Descriptive Analysis of Meteorological Factors in Shanghai

Meteorological factors include temperature and RH and air pollutant PM2.5. The mean ± SD of temperature, RH, and PM2.5 from January 1, 2014, to July 31, 2015, were 16.40 °C ± 7.92 °C, 75.49% ± 5.88%, and 52.46 ± 13.39 μg/m³, respectively.

Correlation Between Meteorological Data and Visits of AOM

The linear correlation analysis revealed a moderate negative correlation between meteorological parameters and AOM-related emergency department visits (Figure 1). Moreover, it demonstrates an inverse correlation (r = − 0.534, P = .018) between RH and the number of emergency department visits for AOM. There were no significant differences between AOM-related emergency department visits and temperature or PM_2.5 (P = .145, P = .158). The lower the RH, the larger the number of AOM-related emergency department visits. The higher the RH, the smaller the number of AOM-related emergency department consultations.

Figure 1.

Linear correlation between the visits of patients with acute otitis media (AOM) and relative humidity.

Meteorological Factors Affect the AOM Visits in the Different Age Groups

We further explore whether the meteorological factors will affect AOM visits in infants, preschool children, and school children. The linear regression model suggested that RH was an independent risk factor for the AOM visits in preschool children (regression coefficient = −10.841, P = .039), which meant that each 1% increase/decrease of RH was associated with a 10.841 decrease/increase of AOM visits in preschool children (Table 2). Besides, neither temperature nor PM_2.5 can affect the number of otitis media visits.

Table 2.

Meteorological Factors Affecting the Visits of AOM in Preschool Children.^a

Model	Unstandardized coefficients	Standard error	Standardized coefficients	t	Significance	VIF
(Constant)	1080.873	445.582		2.426	0.028
PM_2.5	−1.299	2.623	−0.182	−0.495	0.628	3.351
Relative humidity	−10.841	4.784	−0.666	−2.266	0.039	2.149
Temperature	−1.584	4.090	−0.131	−0.387	0.704	2.850
F			3.289
P			.050
R ²			0.397

Abbreviations: AOM, acute otitis media; PM2.5, particulate matter.

^a Dependent variable: visits of AOM in preschool children.

In contrasting, PM_2.5, temperature, and RH were not independent risk factors for the AOM visits in the infants (P = .177, .505, and .061, respectively; Table3) and school-age children (P = .461, .663, and .507, respectively; Table 4).

Table 3.

Meteorological Factors Affecting the Visits of AOM of Infants.^a

Model	Unstandardized coefficients	Standard error	Standardized coefficients	t	Significance	VIF
(Constant)	716.497	292.976		2.446	0.027
PM_2.5	−2.443	1.724	−0.572	−1.417	0.177	3.351
Relative humidity	−6.373	3.145	−0.655	−2.026	0.061	2.149
Temperature	−1.838	2.689	−0.255	−0.683	0.505	2.850

Abbreviations: AOM, acute otitis media; PM2.5, particulate matter.

^a Dependent variable: visits of AOM of infants.

Table 4.

Meteorological Factors Affecting the Visits of AOM Patients in School-Age.^a

Model	Unstandardized coefficients	Standard error	Standardized coefficients	t	Significance	VIF
(Constant)	212.885	342.355		0.622	0.543
PM_2.5	1.524	2.015	0.328	0.756	0.461	3.351
Relative humidity	−2.499	3.676	−0.236	−0.680	0.507	2.149
Temperature	1.398	3.143	0.178	0.445	0.663	2.850

Abbreviations: AOM, acute otitis media; PM2.5, particulate matter.

^a Dependent variable: visits of AOM patients in school age.

Discussion/Conclusion

The Main Findings of This Study

The present study’s novel was to determine the relationships between meteorological parameters and the volume of pediatric AOM visits in Shanghai. By the conclusion of this study, we could infer the correlation between the meteorological factors and the incidence of AOM. We demonstrated an inverse correlation between RH and the number of emergency department visits for AOM (r = − 0.534, P < .01). Neither temperature nor PM_2.5 statistically correlated with the amount of AOM-related emergency department visits. Furthermore, age stratification was introduced into the multivariate linear model of whether meteorological factors would affect otitis media visits. Relative humidity was proved to be an independent risk factor of the AOM visits in preschool children. In contrast, the AOM visits had no significant correlation with the meteorological factors in school children and infants.

Meteorological Parameters and AOM

Meteorological parameters include air temperature, atmospheric pressure, humidity, wind speed, and PM2.5. Temperature and humidity were frequently reported to be statistically associated with respiratory tract infections.^9,15,16 Besides, PM_2.5 was a significant pollutant in China over the years. According to the meta-analysis, PM_2.5 has an adverse impact on asthma emergency department visits after short-term exposure.¹⁹ Thus, we chose climate factors, including temperature, humidity, and PM_2.5, to explore their effects on AOM-related emergency department visits in this study.

Acute otitis media is a common condition affecting children. Approximately 80% of children had at least one episode of AOM when they were 3 years old.¹ It is one of the most frequent reasons for medical consultations in the United States.^1,23 Also, children are uniquely sensitive and vulnerable to climate changes due to physiological mechanisms.²⁴ Therefore, pediatric patients younger than 12 years were the study population.

This study was a retrospective analysis of emergency department’ consultations with AOM recorded in Shanghai, which is characterized by 4 distinctive seasons. In our study, males were significantly more affected than females. Evident seasonal fluctuations in the number of AOM-related emergency department consultations can be observed. The characteristics of pediatric AOM presented in our study are similar to AOM morbidity worldwide.^1,25

We found a negative correlation between RH and the number of visits for AOM in the emergency room. Lower RH was associated with an increased incidence of emergency department visits for AOM, while higher humidity showed protective effects (Figure 1). Acute otitis media is an acute inflammation of the middle ear.²⁶ Both bacteria and respiratory viruses participate and interact in the disease pathogenesis of AOM.^2,3 Viruses such as influenza viruses, rhinovirus, respiratory syncytial virus, and adenoviruses have been detected in the middle ear fluid from children presenting with AOM.^2,3,26 In addition, influenza incidence peaks in cold, dry conditions of temperate winters. However, the hot, wet conditions of tropical rainy seasons discourage the aerosol transmission of influenza.²⁷ Previous studies indicate that RH affects both affect influenza virus transmission and influenza virus survival,^28,29 as well as human rhinovirus,³⁰ human metapneumovirus,³¹ and respiratory syncytial virus.²⁷ An average decrease in absolute humidity increased the risk of human rhinovirus infection by 13% and 20%.³⁰ Acute otitis media is often a sequela of a viral upper respiratory infection. Viral upper respiratory infection is a preexisting condition in 70% of AOM.³² The relationship between humidity and viral stability could be put forth to explain the findings in this study. We deduced that lower humidity promotes viral infection in the respiratory tract and nasopharynx, which led to obstruction of the Eustachian tube and viral AOM.^2,3 Viral AOM increased the risk of bacterial infection and aggravated clinical outcomes of bacterial AOM.²⁶ Colonization of pathogens then occurred within the middle ear, which led to more children having AOM.

Why Humidity Is an Independent Risk Factor of the Incidence of AOM Only in Preschool-Age Children

In different age subgroups, preschool children were susceptible to AOM in low humidity environments. In contrast, the effect of humidity on AOM visits was not significant in infants and school children. First, preschool-age children are cross-infected in kindergartens, and upper respiratory tract infectious diseases are frequent.³³ The Eustachian tube of younger children is shorter and straighter than adults.³⁴ As discussed above, when the humidity is low, the upper respiratory tract mucosa is weakened against specific pathogens.²⁷ It is easy to pass through the undeveloped Eustachian tube into the middle ear cavity. Therefore, high RH protective effects were seen in this age group. Second, the AOM in infants is often related to the feeders’ improper feeding methods and infections. Infants cannot accurately express themselves, and they will not be taken to the ENT emergency department unless they have obvious symptoms of ear scratching and ear discharge. Therefore, the infants’ visits may be underestimated. In our study, for infants, the P is .061 in the regression analysis of the relationship between visits and RH (Table 3). So we believe that the AOM visits in infants are related to RH, but there is no apparent statistical significance. Third, children’s Eustachian tube reaches an adult’s length after 7 years old.³⁴ In school-age children, the Eustachian tube development is close to that of an adult. Even if the upper respiratory tract is infected, it is not easy to pass through the Eustachian tube to the middle ear cavity and cause otitis media. So the AOM incidence in school children is relatively low, and no protective effect of RH was found in school children.

Limitations

This study’s data comes from a hospital from January 1, 2014, to July 31, 2015. There is bias due to incomplete sampling, but because the sample size of this study is relatively large, it can reflect the relationship between the incidence of otitis media and the weather.

In conclusion, humidity has a significant inverse impact on the incidence of AOM only in preschool-age children. Neither temperature nor PM2.5 is associated with the occurrence of AOM.

Footnotes

Authors’ Note

Y-.F.J. contributed to the design of the study and interpretation of data, and drafting the article. D-.D.R. contributed to polishing of the article’s language and structure and early drafting of the article and analyzed the data. W-.W.L. and X.Z. contributed to acquisition of data. W-.W.L. and Y.H. contributed to revising the article critically for important intellectual content. X.Z. and Y.H. contributed to the conception and design of the study. Y-.F.J., W-.W.L., X.Z., and Y.H. contributed to final approval of the version to be submitted. Y-.F.J., W-.W.L., D-.D.R., and Y-.B.H. contributed equally to this work. This study was approved by the Ethics Committee of Eye, Ear, Nose, and Throat Hospital of Fudan University.

Declaration of Conflicting Interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This study was supported by the National Natural Science Foundation of China (NSFC) (Grant Number 81771017).

ORCID iDs

Dong-Dong Ren

Yi-Bo Huang

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