Study Area and Study Subjects
Hualien County is located in the east Taiwan. It has an area of 4629 km2 and a population of 336 733 citizens in January 2012. Approximately 90% of the land area of Hualien County is constituted by mountains. The Central Mountain Chain lays at the west of Hualien and Taitung counties and makes them isolated from the west part of Taiwan. The proportion of Taiwanese aborigines in Hualien County is much higher than that of the whole Taiwan (27.1% vs 2.25%). These attributes make it an appropriate area for cross-cultural researches.
Hualien County has one city, nine rural, and three mountainous townships. The study areas including Siou-Lin, Sin-Chen, Ji-An, and Shou-Feng townships are located at the northern of Hualien County. There are nine public and two private junior high schools in these townships. Four public junior high schools with a proportion of aboriginal student ranging from 40% to 60% were selected as surveyed schools. All students attending these schools were invited to participate in the survey. Consenting students were instructed to complete a structured questionnaire and measured for body height and weight. The study was approved by the Institutional Review Board of Buddhist Tzu Chi General Hospital.
We used a structured questionnaire to obtain data associated with subject's sociodemographic attributes, personal habits, and symptoms of asthma, GERD, and food allergy. The presence of asthmatic symptoms was assessed by a validated video questionnaire with verbal instruction published by the International Study of Asthma and Allergies in Childhood (ISAAC). The ISAAC video questionnaire contains five hierarchical questions and had long been used in large population-based studies in Taiwan.[26,27]
In the present study, two sets of hierarchical questions were used to assess the presence of GERD symptoms. GQ1: Had you have a burning feeling occurred at the upper stomach near the esophagus and this burning feeling was rising up to the chest, throat, or mouth? This question was used as the surrogate of acid reflux and heartburn. GQ2: Had you have a painful sensation in the esophagus behind the sternum when swallowing? The frequency of symptoms was also obtained from whom positive for any one of the two questions.
Body weight and height were measured by a digital system (BW-2200; NAGATA Scale Co. Ltd, Tainan, Taiwan) to the nearest 0.1 kg and 0.1 cm, respectively. Body mass index (BMI) was calculated as (body weight)/(body height)2 (kg/m2). Waist circumference was measured to the nearest 0.1 cm at the level of mid-distance between the bottom of the rib cage and the top of the iliac crest.
In the present study, cumulative prevalence of GERD was defined as positive for GQ1 and/or GQ2 coupling with the symptoms occurred at least once per week. Three-month prevalence was considered as having GERD symptoms at least once per week during the past 3 months before survey. Asthma was considered if response to any one of five ISAAC video questions was positive. Food-related allergic symptoms were defined as the occurrence of diarrhea, skin rash, skin itching, eye itching, red eye, tearing, sneezing, nasal stuffiness, or runny nose after having seafood, eggs, milks, and dairy products. Aborigine ethnicity was defined as both paternal and maternal ethnicities were Taiwan aborigine; and for Han Chinese ethnicity was both Han Chinese. Bi-ethnic was defined as one of the parental ethnicity was Han Chinese, and the other was Taiwan aborigine. The definitions of overweight and obesity were 24.0 ≤ BMI < 27.0 kg/m2 and BMI ≥ 27.0 kg/m2, respectively. Abdominal obesity was defined as having waist circumferences > 90 cm and > 80 cm in males and females, respectively.
Validity and Reliability of GERD Questionnaire
Because of the diagnosis of GERD is currently based on subjective symptoms only, therefore, clinical credibility is the most appropriate index of validity. Consequently, we adapted those reflux symptoms having been frequently used in pediatric subjects[12,15] and had reached great consensus by an international panel of pediatric gastroenterologists. To make sure that these questionnaire items were suitable for the Grade 6 level of literacy, we conducted two pretests. The draft version was first tested with a focus group of three Grade 6 students, and then the modified version was applied to a group of 28 Grade 7 students who joined a summer camp. The questionnaire was modified again before delivered to study subjects.
To test the reliability of GERD questions, a second questionnaire was delivered to a random sample of 91 subjects 2 weeks after the survey. Among 75 responders, the concordant rates of two measurements were 86.7% and 84.2% for lifetime and 3-month, respectively, periods. The corresponding figures of kappa were 0.69 (95% confidence interval [CI]: 0.51–0.86) and 0.54 (95% CI: 0.28–0.80), respectively.
The chi-square test was used to assess the associations between the presence of GERD and personal attributes (e.g. gender, smoking status, ethnicity, and symptoms of asthma and food allergy). Logistic regression models were performed to evaluate the strength of associations between GERD and asthma and food allergy after adjustment the potential confounding effects of other covariates. Subjects with missing data of the regression covariates were excluded from the analyses. All statistical analyses were performed using SAS 9.3 (SAS Institute Inc., Cary, NC, USA). A P value of < 0.05 was considered as statistically significant.
J Gastroenterol Hepatol. 2014;29(2):269-275. © 2014 Blackwell Publishing