Research Indicators and Variables Research Indicators

 Percentage (%) of children with negative Otoacoustic EEG results (OAE (-)) and positive Otoacoustic EEG results (OAE (+)).

 Percentage (%) of children with negative OAE measurement results (OAE (-)) by ear position.

 The proportion (%) of children with negative OAE measurement results (OAE (-)) distributed by age, gender, and geography.

 Rate (%) of right and left tympanometry in children with negative OAE (-) results.

 Rate (%) of right and left stapedial reflexes in children with negative OAE (-) results.

 Percentage (%) of children's hearing loss levels measured by ABR, ASSR or monotone.

 Rate (%) of hearing loss in children.

 Proportion (%) of cases and controls distributed by age and sex.

 The proportion (%) of cases and controls distributed according to the characteristics of the mother's medical history during pregnancy.

 Proportion (%) of cases and controls distributed according to the child's birth history and postnatal interventions.

 Proportion (%) of cases and controls distributed according to characteristics of interventions for children after birth.

 Proportion (%) of cases and controls distributed according to the child's medical history after birth. Research variables

Table 2.3: Definition of research variables

STT

2.6.

Select District/School and Child

participate in research

Screening and Otoacoustic Measurement

1st time at school (7191 children)

Children (+) (6854 children)

Identify the characteristics

object point

Children (-) (337 children) Otoacoustic examination

2nd time at Children's Hospital

Determine the ratio

Hearing loss by age, gender

Type 23 children

false negative

Randomly select 628 children as groups

proof

Identify characteristics and levels

hearing loss

Measure ABR, ASR, Single

ultrasound, ENT endoscopy (314 children)

In-depth Interview 628

mother

Identify the

risk factors

In-depth Interview 314

mother at Children's Hospital

Figure 2.1: Research diagram

2.9 Error correction

The study was conducted in the community, screening a large number of subjects, so the following measures were taken to overcome errors:

 The person who conducts the Cochlear sound measurement for children and performs specialized hearing tests is a doctor (technician) of the National Children's Hospital who has been trained and practiced in the Cochlear sound measurement process according to a unified process.

 OAE measuring machine is a highly accurate measuring machine and is calibrated before each measurement.

 Investigators are trained and practice interviewing: Interviewers are doctors and technicians of the Audiology Center at the National Children's Hospital who have been thoroughly trained in the approach, interviewing methods and interviewing practice according to a unified process.

 Reduce recall errors by taking a careful history, using visual signs of illness, and comparing with the mother and child's health records.

 Research tools including community questionnaires and sample medical records were designed by experts in the field of ENT clearly, easy to understand, tested and edited many times before being used in official data collection in the community and at the National Children's Hospital.

2.10 Data management and processing

Build a data entry and management system. Data is entered twice independently, using Epi data 3.0 software.

Quantitative data were analyzed using SPSS 18.0 software, including descriptive statistics and univariate regression analysis (used in case-control studies). Multivariate linear regression models were also analyzed to find out the patterns of related factors.

The study results are presented as proportions (%), odds ratios (OR) and adjusted ORs in univariate and multivariate analyses with 95% confidence intervals (CI). The  2 test and Fisher'exact test were used to examine group differences.

2.11 Ethics in research

- The research protocol was approved by the Research Ethics Council of the National Institute of Hygiene and Epidemiology.

- The screening examination carried out in Hanoi is approved by the Hanoi Department of Population and Family Planning, Hanoi Department of Health and the National Children's Hospital.

- The study had the consent of the child's parents, family or guardian (Appendix 8: Consent form for participation in the study).

- All results are kept confidential and are for research purposes only.

- Children with suspected hearing loss (through initial screening) will continue to undergo specialized hearing tests at the Audiology Center - National Children's Hospital. (priority examination and free of charge for all services)

- The OAE, ABR or monophonic measurement method is non-pathogenic, painless, non-invasive, so it does not cause bleeding, does not transmit disease and does not cause discomfort to the child.

- Children diagnosed with hearing loss will be advised on care and treatment according to the Ministry of Health's medical examination and treatment regimen for children under 6 years old.

2.12 Some limitations and limitations of the study

Although the study was conducted in kindergartens in Hanoi's inner city using a random lottery method, the study was only conducted in public kindergartens and not in

private kindergartens and kindergartens in Hanoi's inner city. However, according to the Hanoi Department of Education, more than 90.0% of preschool-age children attend these public kindergartens, so the fact that the study was only conducted in public kindergartens may not affect the results of the study. In addition, the study was only conducted in Hanoi's inner city, where the characteristics of hearing loss in preschool children may be different from preschool children in suburban districts of Hanoi.

The otoacoustic stimulation screening method is a suitable method for screening for hearing loss in the community, however, this method only screens for hearing loss due to damage and effects from the cochlea outwards, so children with hearing loss due to causes beyond the cochlea are still not detected. Detection of this type of hearing loss must be done by more specialized methods such as ABR, monophonic. However, due to resource issues such as logistics, funding and time in screening for hearing loss in the community, the use of specialized methods such as ABR, monophonic is difficult to implement. The OAE measurement method is highly sensitive, so using this method in screening for hearing loss in preschool children in the community is still a suitable method.

Due to the nature of case-control studies, which are retrospective studies of factors related to hearing loss in children, some factors related to hearing loss such as the effects of noise on hearing loss and the use of certain antibiotics on hearing loss have not been studied in this study. In fact, the study of noise on hearing loss in children is very complicated and difficult to conduct in this study. In addition, studying the history of use of certain groups of antibiotics in children is also difficult and may give inaccurate results because mothers use drugs and pharmaceuticals for their children according to the instructions and prescriptions of medical staff without thoroughly understanding the type of drug or group of antibiotics that the children use.

CHAPTER 3 RESULTS

3.1. Characteristics of hearing loss in preschool children from 2 to 5 years old

3.1.1 General information about the research subjects

3.1.1.1 Distribution of research subjects by district

Table 3.1: Distribution of study subjects by district (n=7,191)

District

The results of the table above show that a total of 7191 children in 5 districts participated in the study, meeting the required sample size and the distribution of children selected for the study in the 5 districts did not differ. The district with the least number of children was 1171 children, accounting for 16.3%, the district with the highest number of children, accounting for 21.4%.