A case control study is a type of observational study. In this study design, participants are selected to participate depending on their outcome status. Cases are participants with outcome of interest whereas controls are participants who do not have the outcome of interest. These studies estimate the odds ratio or the odds between the exposure and health outcome, however they cannot prove causality. Advantages of case control studies include the following: inexpensive, easy to design and implement, and are used to study rare outcomes. Case control studies are prone to certain research bias but can be addressed by the investigator through careful designing and planning. This paper describes the case control studies, their advantages, bias in case control studies and how to address them, and discuss the steps in how to conduct this type of study design.

BACKGROUND: Recently, the prevalence of food allergies during childhood is increasing, with fruits being common allergens. However, data on allergens that cause fruit and vegetable allergies and pollen-food allergy syndrome (PFAS) in childhood are relatively few. This study aimed to examine the allergens in fruit and vegetable allergies in pediatric patients and to determine the association between fruit and vegetable allergies and PFAS.OBJECTIVE: This study aimed to examine the current status of fruit and vegetable allergies in Japanese children.METHODS: This was a multicenter case series observational study. The participants included children aged <15 years who developed allergic symptoms after eating fruits and vegetables and subsequently received treatment in the Pediatric Department of 6 hospitals in the Osaka Prefecture in Japan during the study period from August 2016 to July 2017. Participants' information was obtained using a questionnaire, and data were obtained by performing several types of allergy tests using blood samples.RESULTS: A total of 97 children (median age, 9 years; 56 males) were included in the study. Apple was the most common allergen, followed by peach, kiwi, cantaloupe, and watermelon. A total of 74 participants (76%) exhibited allergic symptoms due to PFAS; moreover, pathogenesis-related protein-10 (PR-10) was the most common allergen superfamily. On the contrary, in the group where neither PR-10 nor profilin was sensitized, kiwi and banana were the most common allergens, and the age of onset was lower than that in the PFAS group. Specific antibody titer was significantly associated with Birch for Bet v1 and latex for Bet v2 (r = 0.99 and r = 0.89).CONCLUSION: When we examine patients with fruit and vegetable allergies, we should first consider PFAS even in childhood specifically for children greater than 4 years old.
Age of Onset ; Allergens ; Asian Continental Ancestry Group ; Betula ; Child ; Citrullus ; Clinical Study ; Cucumis melo ; Eating ; Food Hypersensitivity ; Fruit ; Humans ; Hypersensitivity ; Japan ; Latex ; Musa ; Observational Study ; Prevalence ; Profilins ; Prunus persica ; Rhinitis ; Rhinitis, Allergic, Seasonal ; Vegetables

PURPOSE: To compare the visual acuity and retinal thickness in patients with an idiopathic epiretinal membrane (ERM) after vitrectomy and membranectomy using two different methods.METHODS: This retrospective observational study included 77 eyes (32 eyes in the diamond-dusted membrane scraper [DDMS] group, and 45 eyes in the intraocular forceps [IOF] group) of 77 patients with idiopathic ERM who underwent pars plana vitrectomy and membranectomy. The main outcome measures were best-corrected visual acuity (BCVA, logMAR) and mean retinal thickness.RESULTS: In the IOF group, the BCVA at postoperative 1 week was significantly lower than at baseline and had improved at 12 weeks after surgery. In the DDMS group, the BCVA at postoperative 1 week showed no significant difference at baseline and had improved at 4 weeks after surgery. The central macular thickness at postoperative 6 months was significantly lower than at baseline (all, p < 0.001); there was no significant difference between the two groups (p = 0.400). The postoperative macular thickness of the DDMS group was significantly lower than that of the IOF group in the inner inferior and outer inferior areas at postoperative 12 weeks and 4 weeks (p = 0.046 and p = 0.039, respectively). Five eyes of the DDMS group and 15 eyes of the IOF group developed cystoid macular edema, 14 eyes of that improved without treatment.CONCLUSIONS: In patients with ERM, the use of DDMS or IOF for vitrectomy and membranectomy both resulted in improved visual acuity and decreased mean retinal thicknesses.
Epiretinal Membrane ; Humans ; Macular Edema ; Membranes ; Observational Study ; Outcome Assessment (Health Care) ; Retinaldehyde ; Retrospective Studies ; Surgical Instruments ; Visual Acuity ; Vitrectomy

study was to investigate whether androgen deprivation therapy (ADT) with gonadotropin-releasing hormone agonist (GnRHa) in prostate cancer (Pca) patients is associated with cardiovascular disease in the cohort based from the entire Korean population.METHODS: Using the Korean National Health Insurance database, we conducted an observational study of 579,377 men who sought treatment for Pca between January 1, 2012 and December 31, 2016. After excluding patients with previously diagnosed cardiovascular disease or who had undergone chemotherapy, we extracted the data from 2,053 patients who started GnRHa (GnRHa users) and 2,654 men who were newly diagnosed with Pca (GnRHa nonusers) between July 1, 2012, and December 31, 2012, with follow-up through December 31, 2016. The primary outcomes were cerebrovascular attack (CVA) and ischemic heart disease (IHD).RESULTS: GnRHa users were older, were more likely to reside in rural areas, had lower socioeconomic status, and had more comorbidities than nonusers (all P < 0.050). Although GnRHa users had an increased incidence of CVA and IHD (P = 0.013 and 0.048, respectively) in univariate analysis, GnRHa use was not associated with the outcomes in multivariate analysis. Furthermore, the cumulative duration of ADT was not associated with the outcomes whereas the associations between age at diagnosis with all diseases were significant.CONCLUSION: Our complete enumeration of the Korean Pca population shows that ADT is not associated with increased risks of cardiovascular disease.]]>
Antineoplastic Agents ; Cardiovascular Diseases ; Cohort Studies ; Comorbidity ; Diagnosis ; Drug Therapy ; Follow-Up Studies ; Gonadotropin-Releasing Hormone ; Humans ; Incidence ; Male ; Morinda ; Multivariate Analysis ; Myocardial Ischemia ; National Health Programs ; Observational Study ; Passive Cutaneous Anaphylaxis ; Prostate ; Prostatic Neoplasms ; Social Class

study evaluated the clinical characteristics of chronic cough in Korea and the efficacy of the KATRD guidelines.METHODS: This was a multi-center, retrospective observational study conducted in Korea. The participants were over 18 years of age. They had coughs lasting more than 8 weeks. Subjects with current pulmonary diseases, smokers, ex-smokers with more than 10 pack-years or who quit within the past 1 year, pregnant women, and users of cough-inducing medications were excluded. Evaluation and management of cough followed the KATRD cough-management guidelines.RESULTS: Participants with chronic cough in Korea showed age in the late forties and cough duration of more than 1 year. Upper airway cough syndrome was the most common cause of cough, followed by cough-variant asthma (CVA). Gastro-esophageal reflux diseases and eosinophilic bronchitis were less frequently observed. Following the KATRD cough-management guidelines, 91.2% of the subjects improved after 4 weeks of treatment. Responders were younger, had a longer duration of cough, and an initial impression of CVA. In univariate and multivariate analyses, an initial impression of CVA was the only factor related to better treatment response.CONCLUSION: The causes of chronic cough in Korea differed from those reported in other countries. The current Korean guidelines proved efficient for treating Korean patients with chronic cough.]]>
Asthma ; Bronchitis ; Cohort Studies ; Cough ; Diagnosis ; Disease Management ; Eosinophils ; Epidemiology ; Female ; Gastroesophageal Reflux ; Humans ; Korea ; Lung Diseases ; Multivariate Analysis ; Observational Study ; Pregnant Women ; Retrospective Studies ; Tuberculosis

observational study was conducted from February 2006 to April 2018 at 11 hospitals in Korea. Eligible patients with recurrent US received an ILR to diagnose recurrent syncope and document arrhythmia.RESULTS: A total of 173 US patients (mean age, 67.6 ± 16.5 years; 107 men [61.8%]) who received an ILR after a negative conventional workup were enrolled. During a mean follow-up of 9.4 ± 11.1 months, 52 patients (30.1%) had recurrent syncope, and syncope-correlated arrhythmia was confirmed in 34 patients (19.7%). The ILR analysis showed sinus node dysfunction in 24 patients (70.6%), supraventricular tachyarrhythmia in 4 (11.8%), ventricular arrhythmia in 4 (11.8%), and sudden atrioventricular block in 2 (5.9%). Overall, ILR detected significant arrhythmia in 99 patients (57.2%) irrespective of syncope. Among patients with clinically relevant arrhythmia detected by ILR, PM implantation was performed in 60 (34.7%), an intra-cardiac defibrillator in 5 (2.9%), and catheter ablation in 4 (2.3%). In a Cox regression analysis, history of paroxysmal atrial fibrillation (PAF) (hazard ratio [HR], 2.34; 95% confidence interval [CI], 1.33–4.12; P < 0.01) and any bundle branch block (BBB) (HR, 2.52; 95% CI, 1.09–5.85; P = 0.03) were significantly associated with PM implantation.CONCLUSION: ILR is useful for detecting syncope-correlated arrhythmia in patients with US. The risk of PM is high in US patients with a history of PAF and any BBB.]]>
Arrhythmias, Cardiac ; Atrial Fibrillation ; Atrioventricular Block ; Bundle-Branch Block ; Catheter Ablation ; Defibrillators ; Follow-Up Studies ; Humans ; Korea ; Male ; Observational Study ; Retrospective Studies ; Sick Sinus Syndrome ; Syncope ; Tachycardia

observational study (intensivist crossover design) of medical patients who were transferred to two ICUs from general wards between September 2017 and February 2019 at one academic hospital. We compared the ICU outcomes according to the ICU type (ICU with resident management under high-intensity intensivist staffing vs. ICU with direct management by intensivists without residents).RESULTS: Of 314 enrolled patients, 70 were primarily managed by residents, and 244 were directly managed by intensivists. The latter patients showed better ICU mortality (29.9% vs. 42.9%, P = 0.042), lower cardiopulmonary resuscitation (CPR) (10.2% vs. 21.4%, P = 0.013), lower continuous renal replacement therapy (CRRT) (24.2% vs. 40.0%, P = 0.009), and more advanced care planning decisions before death (87.3% vs. 66.7%, P = 0.013) than the former patients. The better ICU mortality (hazard ratio, 1.641; P = 0.035), lower CPR (odds ratio [OR], 2.891; P = 0.009), lower CRRT (OR, 2.602; P = 0.005), and more advanced care planning decisions before death (OR, 4.978; P = 0.007) were also associated with intensivist direct management in the multivariate cox and logistic regression analysis.CONCLUSION: Intensivist direct management might be associated with better ICU outcomes than resident management under the supervision of an intensivist. Further large-scale prospective randomized trials are required to draw a definitive conclusion.]]>
Cardiopulmonary Resuscitation ; Critical Care ; Cross-Over Studies ; Humans ; Intensive Care Units ; Internal Medicine ; Internship and Residency ; Logistic Models ; Medical Staff ; Mortality ; Observational Study ; Organization and Administration ; Patients' Rooms ; Prospective Studies ; Renal Replacement Therapy ; Retrospective Studies ; Running ; Survival Rate

study reports the clinical use of two sevoflurane-based anesthetic techniques in dogs undergoing craniectomy. Twenty-one animals undergoing elective rostrotentorial or transfrontal craniectomy for brain tumor excision, anesthetized with sevoflurane, were enrolled in this retrospective, observational study. Anesthetic records were allocated to two groups: Sevo-Op (sevoflurane and short acting opioid infusion): 8 dogs and Sevo-Dex (sevoflurane and dexmedetomidine infusion): 13 dogs. Average mean arterial pressure (MAP), heart rate, end-tidal carbon dioxide, end-tidal sevoflurane and intraoperative infusion rates during surgery were calculated. Presence of intra-operative and post-operative bradycardia, tachycardia, hypotension, hypertension, hypothermia, hyperthermia was recorded. Time to endotracheal extubation, intraoperative occurrence of atrioventricular block, postoperative presence of agitation, seizures, use of labetalol and dexmedetomidine infusion were also recorded. Data from the two groups were compared with Fisher's exact test and unpaired t tests with Welch's correction. Odds ratio (OR) and 95% confidence interval (CI) were calculated for categorical variables. Intra-operatively, MAP was lower in Sevo-Op [85 (± 6.54) vs. 97.69 (± 7.8) mmHg, p = 0.0009]. Time to extubation was longer in Sevo-Dex [37.69 (10–70) vs. 19.63 (10–25), p = 0.0033]. No differences were found for the other intra-operative and post-operative variables investigated. Post-operative hypertension and agitation were the most common complications (11 and 12 out of 21 animals, respectively). These results suggest that the infusion of dexmedetomidine provides similar intra-operative conditions and post-operative course to a short acting opioid infusion during sevoflurane anesthesia in dogs undergoing elective rostrotentorial or transfrontal intracranial surgery.]]>
Airway Extubation ; Anesthesia ; Animals ; Arterial Pressure ; Atrioventricular Block ; Bradycardia ; Brain Neoplasms ; Carbon Dioxide ; Dexmedetomidine ; Dihydroergotamine ; Dogs ; Fever ; Heart Rate ; Hypertension ; Hypotension ; Hypothermia ; Labetalol ; Neurosurgery ; Observational Study ; Odds Ratio ; Retrospective Studies ; Seizures ; Tachycardia

STUDY DESIGN: A retrospective observational study was performed. PURPOSE: We investigated the prevalence of sarcopenia in dropped head syndrome (DHS), and the relationship between biochemical markers, including major advanced glycation end products (AGEs), pentosidine, and DHS in older women. OVERVIEW OF LITERATURE: AGEs have been implicated in the pathogenesis of sarcopenia. METHODS: We studied 13 elderly women with idiopathic DHS (mean age, 77.2 years) and 20 healthy volunteers (mean age, 74.8 years). We used a bioelectrical impedance analyzer to analyze body composition, including appendicular skeletal muscle mass index (SMI; appendicular lean mass [kg]/[height (m)]2). Cervical sagittal plane alignment, including C2–C7 sagittal vertical axis (C2–C7SVA), C2–C7 angle, and C2 slope (C2S), was measured. Biochemical markers, such as serum and urinary pentosidine, serum homocysteine, 1, 25-dihydroxyvitamin D, and 25-hydroxyvitamin D, were measured. The level of each variable was compared between DHS and controls. The relationship between biochemical markers and DHS was examined. RESULTS: Sarcopenia (SMI < 5.75) was observed at a high prevalence in participants with DHS (77% compared to 22% of healthy controls). Height, weight, femoral bone mineral density, appendicular lean mass, total lean mass, and SMI all had significantly lower values in the DHS group. Serum and urinary pentosidine, and serum homocysteine were significantly higher in the DHS group compared to controls. Analysis of cervical alignment revealed a significant positive correlation of serum pentosidine with C2–C7SVA and C2S. CONCLUSIONS: Sarcopenia was involved in DHS, and high serum pentosidine levels are associated with severity of DHS in older women.
Aged ; Biomarkers ; Body Composition ; Bone Density ; Electric Impedance ; Female ; Glycosylation End Products, Advanced ; Head ; Healthy Volunteers ; Homocysteine ; Humans ; Muscle, Skeletal ; Neck Muscles ; Observational Study ; Prevalence ; Retrospective Studies ; Sarcopenia

PURPOSE: The purpose of this study was to evaluate chemotherapy patterns and changes in quality of life (QOL) during first-line palliative chemotherapy for Korean patients with unresectable or metastatic/recurrent gastric cancer (GC). MATERIALS AND METHODS: Thiswas a non-interventional, multi-center, prospective, observational study of 527 patients in Korea. QOL assessments were conducted using the European Organization for Research and Treatment of Cancer (EORTC) Quality of Life Questionnaires (QLQ)-C30 and QLQ-STO22 every 3 months over a 12-month period during first-line palliative chemotherapy. The specific chemotherapy regimens were selected by individual clinicians. RESULTS: Most patients (93.2%) received combination chemotherapy (mainly fluoropyrimidine plus platinum) as their first-line palliative chemotherapy. The median progression-free survival and overall survival were 8.2 and 14.8 months, respectively. Overall, “a little” changes (differences of 5-10 points from baseline)were observed in some of the functioning or symptom scales; none of the QOL scales showed either “moderate” or “very much” change (i.e., ≥ 11 point difference from baseline). When examining the best change in each QOL domain from baseline, scales related to some aspects of functioning, global health status/QOL, and most symptoms revealed significant improvements (p < 0.05). Throughout the course of first-line palliative chemotherapy, most patients' QOL was maintained to a similar degree, regardless of their actual response to chemotherapy. CONCLUSION: This observational study provides important information on the chemotherapy patterns and QOL changes in Korean patientswith advanced GC. Overall, first-line palliative chemotherapy was found to maintain QOL, and most parameters showed an improvement compared with the baseline at some point during the course.
Disease-Free Survival ; Drug Therapy* ; Drug Therapy, Combination ; Global Health ; Humans ; Korea ; Observational Study ; Prospective Studies ; Quality of Life* ; Stomach Neoplasms* ; Weights and Measures