BackgroundSelection bias is a systematic error in epidemiologic studies that may seriously distort true measures of associations between exposure and disease. Observational studies are highly susceptible to selection bias, and researchers should therefore always examine to what extent selection bias may be present in their material and what characterizes the bias in their material. In the present study we examined long-term participation and consequences of loss to follow-up in the studies Respiratory Health in Northern Europe (RHINE), Italian centers of European Community Respiratory Health Survey (I-ECRHS), and the Italian Study on Asthma in Young Adults (ISAYA).MethodsLogistic regression identified predictors for follow-up participation. Baseline prevalence of 9 respiratory symptoms (asthma attack, asthma medication, combined variable with asthma attack and/or asthma medication, wheeze, rhinitis, wheeze with dyspnea, wheeze without cold, waking with chest tightness, waking with dyspnea) and 9 exposure-outcome associations (predictors sex, age and smoking; outcomes wheeze, asthma and rhinitis) were compared between all baseline participants and long-term participants. Bias was measured as ratios of relative frequencies and ratios of odds ratios (ROR).ResultsFollow-up response rates after 10 years were 75% in RHINE, 64% in I-ECRHS and 53% in ISAYA. After 20 years of follow-up, response was 53% in RHINE and 49% in I-ECRHS. Female sex predicted long-term participation (in RHINE OR (95% CI) 1.30(1.22, 1.38); in I-ECRHS 1.29 (1.11, 1.50); and in ISAYA 1.42 (1.25, 1.61)), as did increasing age. Baseline prevalence of respiratory symptoms were lower among long-term participants (relative deviations compared to total baseline population 0-15% (RHINE), 0-48% (I-ECRHS), 3-20% (ISAYA)), except rhinitis which had a slightly higher prevalence. Most exposure-outcome associations did not differ between long-term participants and all baseline participants, except lower OR for rhinitis among ISAYA long-term participating smokers (relative deviation 17% (smokers) and 44% (10–20 pack years)).ConclusionsWe found comparable patterns of long-term participation and loss to follow-up in RHINE, I-ECRHS and ISAYA. Baseline prevalence estimates for long-term participants were slightly lower than for the total baseline population, while exposure-outcome associations were mainly unchanged by loss to follow-up.

In the three Italian centres involved in the European CommunityRespiratory Health Survey (ECRHS), prevalence of asthma-like symptoms was assessed through a mailback questionnaire. Since the nonresponse rate was not negligible, ranging 10-18%, we investigated whether nonresponse bias affected the results and, if so, whether the bias could be eliminated from the final estimates of prevalence.A screening questionnaire was sent by mail to 7,000 randomly selected subjects 20-44 yrs of age, and nonresponders were contacted again by phone. Additional information was collected on a subsample of the respondents through a clinical interview.A logistic regression analysis showed that, except for one symptom (awakening for coughing), symptom prevalence significantly decreased from the first to the subsequent contact, when controlling for age, sex, centre and season of interview. The decrease in symptom prevalence was largely independent of smoking habits and socioeconomic status, and was seemingly caused by a symptom-related selfselection. When correcting results according to a linear regression model, observed estimates appeared to be slightly overestimated, by 4-10%. A simulation with the Italian data showed that the bias increased steeply at nonresponse rate higher than 30%, a situation quite common in asthma surveys.In conclusion, nonresponse bias affects the results of ECRHS in Italy, slightly inflating prevalence estimates. To make reliable comparisons on international data in the presence of different nonresponse rates, a correction of the observed prevalence seems necessary.

SummaryThis population-based survey aimed to determine the prevalence of known diabetes mellitus on 31 December 1986, and to assess all-cause mortality in the subsequent 5 years (1987)(1988)(1989)(1990)(1991) in Verona, Italy. In the study of prevalence, 5996 patients were identified by three independent sources: family physicians, diabetes clinics, and drug prescriptions for diabetes. Mortality was assessed by matching all death certificates of Verona in 1987-1991 with the diabetic cohort. Overall diabetes prevalence was 2.61% (95 % confidence interval 2.56-2.67). Prevalence of insulin-dependent and non-insulin-dependent diabetes mellitus was 0.069 % (0.059-0.078) and 2.49 % (2.43-2.54), respectively. Diabetes prevalence sharply increased after age 35 years up to age 75-79, and finally declined. Prevalence was higher in men up to age 69 years, in women after age 75 years. Of the diabetic cohort 1260 patients (592 men, 668 women) died by 31 December 1991, yielding an overall standardized mortality ratio of 1.46 (CI 1.38-1.54). Even though the differences narrowed with age, mortality rates in the diabetic cohort were higher than in the non-diabetic population at all ages. Women aged 65-74 years showed observed/expected ratio higher than men (2.27, CI 1.92-2.66, vs 1.50, CI 1.30-1.72), while in other age groups the sex-related differences were not significant. Pharmacological treatment of diabetes was associated with an excess mortality, while treatment with diet alone showed an apparent protective effect on mortality (observed/expected ratio 0.73, CI 0.58-0.92). In conclusion, in Verona diabetes has a prevalence similar to that of other European countries, and is associated with an excess mortality which is observed in both sexes, at all ages, and with any anti-diabetic pharmacologic treatment. Diet-treated diabetes seems to be associated with a significant reduction in the mortality risk. [Diabetologia (1995) 38: 318-325]

This study demonstrates that the prevalence of allergic rhinitis in northern Italy is similar to the prevalence observed in other European countries and that this disease is more common in urban areas.

BackgroundIncreased bronchial responsiveness is characteristic of asthma. Gas cooking, which is a major indoor source of the highly oxidant nitrogen dioxide, has been associated with respiratory symptoms and reduced lung function. However, little is known about the effect of gas cooking on bronchial responsiveness and on how this relationship may be modified by variants in the genes GSTM1, GSTT1 and GSTP1, which influence antioxidant defences.MethodsThe study was performed in subjects with forced expiratory volume in one second at least 70% of predicted who took part in the multicentre European Community Respiratory Health Survey, had bronchial responsiveness assessed by methacholine challenge and had been genotyped for GSTM1, GSTT1 and GSTP1-rs1695. Information on the use of gas for cooking was obtained from interviewer-led questionnaires. Effect modification by genotype on the association between the use of gas for cooking and bronchial responsiveness was assessed within each participating country, and estimates combined using meta-analysis.ResultsOverall, gas cooking, as compared with cooking with electricity, was not associated with bronchial responsiveness (β=−0.08, 95% CI −0.40 to 0.25, p=0.648). However, GSTM1 significantly modified this effect (β for interaction=−0.75, 95% CI −1.16 to −0.33, p=4×10−4), with GSTM1 null subjects showing more responsiveness if they cooked with gas. No effect modification by GSTT1 or GSTP1-rs1695 genotypes was observed.ConclusionsIncreased bronchial responsiveness was associated with gas cooking among subjects with the GSTM1 null genotype. This may reflect the oxidant effects on the bronchi of exposure to nitrogen dioxide.

Bacterial ecology was studied in 1114 newborns (355 at term, 759 preterm) admitted to a neonatal intensive care unit (NICU) during a three year period. Bacterial samples were taken in each newborn from external ear canal, pharynx and eyes in all patients, and from endotracheal tube, umbilical catheter and blood in selected patients. The predominant flora was characterized by gram-positive microorganisms (63.53%), Staphylococcus epidermidis representing 34.68% of all isolated strains. S. epidermidis isolation increased significantly with time (p < 0.002) and was highest in summer. The percentage of S. epidermidis resistant strains to oxacillin (63.8%) and to amikacin (17.8%) was high. This is the antimicrobial combination we commonly employ as empirical treatment of suspected bacterial infection in our NICU. Knowledge of characteristics of local microbial flora seems important in order to optimize preventive and therapeutic policies for neonatal infections.

No abstract

No abstract