Incidence and prognosis ofasthma and wheezing

Objective-To describe the incidence and prognosis of wheezing illness from birth to age 33 and the relation of incidence to perinatal, medical, social, environmental, and lifestyle factors. Design-Prospective longitudinal study. Setting-England, Scotland, and Wales. Subjects-18 559 people born on 3-9 March 1958. 5801 (31%) contributed information at ages 7, 11, 16, 23, and 33 years. Attrition bias was evaluated using information on 14 571 (79%) subjects. Main outcome measure-History of asthma, wheezy bronchitis, or wheezing obtained fiom interview with subjects' parents at ages 7, 11, and 16 and reported at interview by subjects at ages 23 and 33. Results-The cumulative incidence ofwheezing illness was 18% by age 7, 24% by age 16, and 43% by age 33. Incidence during childhood was strongly and independently associated with pneumonia, hay fever, and eczema. There were weaker independent associations with male sex, third trimester antepartum haemorrhage, whooping cough, recurrent abdominal pain, and migraine. Incidence from age 17 to 33 was associated strongly with active cigarette smoking and a history of hay fever. There were weaker independent associations with female sex, maternal albuminuria during pregnancy, and histories of eczema and migraine. Maternal smoking during pregnancy was weakly and inconsistently related to childhood wheezing but was a stronger and significant independent predictor of incidence after age 16. Among 880 subjects who developed asthma or wheezy bronchitis from birth to age 7, 50% had attacks in the previous year at age 7; 18% at 11, 10% at 16, 10% at 23, and 27% at 33. Relapse at 33 after prolonged remission of childhood wheezing was more common among current smokers and atopic subjects. Conclusion-Atopy and active cigarette smoking are major influences on the incidence and recurrence ofwheezing during adulthood. Department of Public Health Sciences, St George's Hospital Medical School, London SW17 ORE David P Strachan, reader in epidemiology Barbara K Butland, lecturer in medical statistics H Ross Anderson, professor of epidemiology and public health Correspondence to: Dr Strachan. BMJ 1996;312:1195-99 Introduction Most epidemiological studies of asthma and other wheezing illnesses have been cross sectional, in which existing (prevalent) cases are compared with healthy subjects. Prevalence is influenced by both incidence and prognosis. Investigation of the causes of disease should ideally focus on new (incident) cases and the healthy population from which they are drawn, whereas factors which influence the persistence of symptoms are of greater relevance to affected people.' In this paper we describe the pattern ofincidence and prognosis of wheezing illness in a large, nationally representative sample of young British adults who have been contacted at intervals since birth.24We also examined the relation of incidence to a range of perinatal, medical, social, environmental, and lifestyle factors. Subjects and methods The British national child development study (1958 cohort) is a longitudinal study of all people in England, Scotland, and Wales born during one week, 3-9 March 1958. It started as a study of perinatal morbidity and mortality' and subsequently included immigrants with the same birth dates. The cohort was followed up at ages 7, 11, and 16 by parental interview and examination by school medical officers.6 7 Cohort members were interviewed at ages 23 and 33.8 At ages 7, 11, 16, and 23 questions were asked relating to a history of asthma or wheezy bronchitis. At age 33 a more inclusive question was asked, referring to a history of wheezing, irrespective of diagnosis, and respondents were asked if they had ever had asthma (see appendix). The incidence of wheezing illness was assessed over three periods: birth to 7,8 to 16, and 17 to 33 years. As in previous reports,24 we considered incident cases to be subjects without a history of asthma or wheezy bronchitis at all previous follow ups whose parents reported that they had ever had asthma or wheezy bronchitis at ages 7, 11, and 16; subjects who reported asthma or wheezy bronchitis since their 16th birthday at age 23; or subjects who reported having ever had asthma or wheezing, or both, at age 33. Subjects with a history of asthma or wheezy bronchitis at previous follow ups were excluded from the denominator for the second and third periods. Persistence of wheezing at each follow up was assessed by responses indicating one or more attacks of asthma or wheezy bronchitis in the previous year at ages 7, 11, 16, and 23 and by a report of wheezing or whistling in the chest in the previous year at age 33. There was no specific inquiry about attacks of asthma in the previous year at age 33. The association of incidence with a wide range of perinatal, medical, social, environmental, and lifestyle variables was assessed by cross tabulation and multiple logistic regression using SAS.9 Results Originally, 17 414 births were included in the 1958 perinatal mortality survey, and a further 1145 subjects were included subsequently. At age 7, 14 571 (79% of 18 559) contributed information on asthma and bronchitis with wheezing. A history of wheezing illness at ages 7, 11, 16, 23, and 33 was available for 5801 subjects (31% of 18 559), including 1046 with a history of asthma or wheezy bronchitis by the age of 7. Information on the occurrence of wheezing attacks in the previous year was complete at each follow up for 880 of these subjects (84% of 1046). Table 1 shows the incidence and prognosis of wheezing illness in the group with complete linked data and the corresponding values calculated using all available information.2 The estimates differ only slightly, suggesting minimal bias due to sample attrition.