Methodology

Cohorts/sampling scheme

Cohorts

The Leicestershire respiratory cohorts consist of 3 separate stratified (by age and ethnicity) random samples of preschool children (Table 1).
 

 
These children were sampled from among all children in the respective strata born and living in Leicestershire at the time of recruitment as recorded in the Leicestershire Health Authority Child Health Database.

Surveys/response rate

Surveys

All cohorts have been followed up in quite regular intervals through postal questionnaires. Several surveys included lab measurements and interviews in nested subsamples (Table 2).
 

Response rates

Response rates were good for initial surveys but steadily declined in later follow-ups (Table 3). A major reason for this attrition has been changes in addresses. Currently we are trying to obtain updated addresses for all cohorts so as to reach as many members of the original samples as possible.
 

Questionnaire data

Based on the 1990 questionnaire which had been developed de novo, a new questionnaire was designed in 1998 that has been used in similar form in all subsequent surveys. Compared to the 1990 questionnaire, the new questionnaire included further questions on symptoms (e.g. upper respiratory symptoms) and environmental exposures. Some questions were also adapted to the wording used in International Study of Asthma and Allergies in Childhood (ISAAC).

The information collected includes

1. Wheeze and cough:

  • Wheeze ever and age at onset
  • Frequency and duration of wheeze attacks in the last 12 months
  • Triggers of wheeze such as colds, exercise, foods, beverages, pollen, house dust etc.
  • Interference with sleep and speech limitation due to wheeze
  • Occurrence of cough with or apart from colds
  • Triggers of cough such as colds, exercise, foods, beverages, pollen, house dust etc.
  • Doctor diagnosed asthma or bronchitis
  • Childs history of pneumonia, whooping cough, bronchiolitis, and other chest infections

2. Ear, nose, throat symptoms:

  • Frequency of colds or flu in the past 12 months
  • Problems with sneezing, running or blocked nose, snoring, in the past 12 months
  • Interference of these symptoms with daily activities and sleep
  • Prevalence of ear infections, throat infections, and croup in the past 12 months

3. Treatment and Healthcare:

  • Hospitalization and frequency of GP visits due to wheezing symptoms
  • Use of asthma medication, use of inhalers

4. Environment:

  • Attendance of day care, nursery or play school
  • Fuel used for heating and for cooking
  • Contact with animals
  • Sibship and household structure
  • Smoking exposure
  • Parent’s history of wheezing, asthma, bronchitis, hayfever, eczema
  • Self-assessed ethnicity and main language spoken
  • Education, work
  • Physical activities
  • Traffic density at home

Physiological/routine data

Lab measurements include

in 1992-1994:

  • Growth (weight, height)
  • Clinical status
  • Noisy breathing, cough, nasal discharge, skin rash
  • and eczema
  • Skin prick tests (cat dander, dog dander, Dermatophagoides pteronyssinus, mixed grass pollens, histamine and negative controls)
  • Spirometry
  • Methacholine bronchial challenge Using a 20% decrease in transcutaneous oxygen tension to assess response (PC20 – tc-PO2) 
  • Peak flow and symptom diary during two weeks
  • Overnight cough monitoring

in 2005-2006:

  • Growth (weight, height)
  • Blood pressure
  • Skin prick tests (cat dander, dog dander, Dermatophagoides pteronyssinus, mixed grass pollens, histamine and negative controls)
  • Pre- and post-bronchodilator spirometry
  • Methacholine bronchial challenge using a 20% decrease in FEV1 to assess response. (PC20 – FEV1)
  • Exhaled NO
  • Blood or buccal smear for genetic analyses
  • Serum aliquots for IgE and other measurements

in 2008-2010: 

  • Growth (weight, height, skinfold thickness, waist circumference)
  • Blood pressure
  • Skin prick tests (cat dander, dog dander, Dermatophagoides pteronyssinus, mixed grass pollens, histamine and negative controls)
  • Pre- and post-bronchodilator spirometry
  • Methacholine bronchial challenge using a 20% decrease in FEV1 to assess response. (PC20 – FEV1)
  • Exhaled NO 
  • Blood or buccal smear for genetic analyses
Routine data:

The following data are available for all children from all cohorts. If not otherwise noted, these data were obtained from the Leicestershire Health Authority Child health database.

  • Birth notification and perinatal details: gender; date of birth; number of older siblings; gestational age; birth weight
  • Demographic and socio-economic information: mother’s occupation, ethnicity, religion, country of birth and language; father’s occupation at time of child’s birth
  • Health visitor records: complete information on growth (height, weight, head circumference at 1, 8, 18, 38 months); complete records of childhood immunizations (type of vaccine, dose, date); routine development tests
  • Townsend score (1991 census data)
  • Proximity to roads and modelled exposure to air pollutants based on postcode (Indic–Airviro dispersion model Version 2.2, Swedish Meteorological and Hydrological Institute, Norrköping, Sweden)
  • Home addresses