Manchester Asthma and Allergy Study
The Manchester Asthma and Allergy Study is an unselected, population-based prospective study which follows the development of asthma and other atopic disorders in a cohort of children. The setting is the maternity catchment area of Wythenshawe and Stepping Hill Hospitals, comprising of 50 square miles of South Manchester and Cheshire, UK, a stable mixed urban-rural population.
Screening & Recruitment
All pregnant women were screened for eligibility at antenatal visits (8th-10th week of pregnancy) The study began recruitment in 1995 . Once both parents had completed questionnaires and skin prick testing, a full explanation of the proposed future follow-up for the child was given.
The children have been followed prospectively and were invited back to clinic for an assessment around their 1st, 3rd, 5th, 8th and 11th birthdays. Age 13-16 years follow up is currently underway. The parents and children completed questionnaires regarding symptoms of asthma, eczema, hay fever and food allergies (a validated ISAAC questionnaire was administered by the study nurse). The children had their lung function tested as well as skin testing for allergies (see below). In addition, most of the children provided blood for further allergy testing and for genetic studies.
Atopic sensitization was ascertained by skin prick testing (D pteronyssinus, cat, dog, grasses, moulds, milk, egg, peanut etc). We defined sensitization as a mean weal diameter 3mm greater than negative control to at least one of the allergens tested. We also measured specific serum IgE to mite, cat, dog, grasses, milk, egg and peanut by ImmunoCAPTM.
At age 3 – 11 years, specific airway conductance was measured using whole-body plethysmography by a single-step procedure from the simultaneously measured changes of respiratory flow and plethysmographic pressure, omitting the measurement of thoracic gas volume. Measurements were carried out during normal tidal breathing using a modified facemask fitted with a non-compressible mouthpiece. Three measurements of sGaw were performed, and each was calculated from the means of 5 consecutively measured technically acceptable loops (each child performed at least 15 loops). The median of these 3 measurements of effective sGaw was used in the analysis.
At age 5, 8 and 11 dynamic lung volumes and expiratory flow were performed using a pneumotachograph system with animated incentive software. Subjects were asked to inhale to total lung capacity (TLC), then instructed to perform a forced expiration, through a mouthpiece, to residual volume (RV). The test was repeated at intervals of 30 seconds until 3 technically acceptable traces were obtained. Forced expiratory volume in one second (FEV1) and Forced vital capacity (FVC) were recorded. All children were asymptomatic at time of testing. β2-agonists were withheld for at least 4 hours prior to testing.
Dry air challenge: At the 5-year follow-up, airway reactivity was assessed by means of an Eucapnic Voluntary Hyperventilation (EVH) challenge. Subjects hyperventilated gas containing 21% O2, 5% CO2, remainder N2 with a water content <10mg/L for 6 minutes at a ventilation rate of 75% of maximum voluntary ventilation (estimated pre-challenge as FEV1x22.5). sRaw was measured at baseline and 2, 5 and 10 minutes post challenge. The highest sRaw value measured post challenge was recorded. Parents were asked to withhold from giving the children short acting bronchodilators for 6 hours and long acting bronchodilators for 12 hours prior to testing.
Methacholine Challenge: At the 8 and 11 year follow-up, airway reactivity was assessed by methacholine challenge using a 5 step protocol performed according to ATS guidelines. The methacholine (acetyl-β-methylcholine chloride) solutions were prepared with sterile normal saline Quadrupling doses of methacholine (0.0625 – 16.0 mg/mL) were delivered to subjects via a DeVilbiss 646 nebuliser and a KoKo dosimeter. The test was explained to the subject and the best baseline FEV1 measurement performed in the wedge bellow spirometer was recorded. The predicted FEV1 was calculated and if the measured value was <1.0 l or less than 60% predicted the test was not performed. If the child was unable to produce reproducible FEV1 measurements the procedure was abandoned. Assuming the child met the criteria to continue, the 20% drop from the child’s baseline value was calculated so that the operator would know when to stop the test. After normal tidal expiration to FRC (functional residual capacity) the dosimeter was triggered at the onset of inspiration, and the subject asked to inhale slowly and deeply over 6 s. Subjects were instructed to hold their breath for 5 s, followed by slow exhalation for 5 s. FEV1 was measured 30 and 90 seconds after 5 inhalations of each dose of methacholine. The challenge was stopped when either a 20% fall in FEV1 was observed, or the maximum methacholine concentration had been administered with a fall of less than 20% in FEV1.
Data from primary care medical records
The United Kingdom health care system is unique as it is free for all residents and there are no financial barriers to access primary care. Therefore almost the entire UK population is registered with General Practitioners (GPs). The medical record follows the patient as they change GP and provides a full record of all health care contacts. GPs are legally required to maintain accurate records of all medical encounters of their patients, including retention of hospital admission discharge letters, outpatient appointments and all prescriptions; this record follows the patient throughout life.
Access to primary care medical records was approved by 20 relevant Primary Care Trusts. Eligible practices were contacted and invited to participate in the study either by both postal information packs and phone calls (GP practices with two or more children) or by post only (GP practices with a single study participant). Data access and manual extraction were performed during arranged visits to each GP practice. GP practices which refused access to premises or had only one study child registered contributed by sending copies of subjects’ medical records.
A trained paediatrician extracted data from electronic and paper-based primary care medical records including prescriptions, acute wheeze episodes, oral steroid prescriptions and hospital admissions for asthma or wheeze during the first 8 years of life. To ensure consistency during data extraction, all GP practices were visited by both a research physician and a study nurse for the first 9 months. Timing, type of visit, symptoms, indication and prescriptions for each encounter were noted. We calculated child’s age in days for each event Presence of wheeze and asthma diagnosis was recorded. Prescription information included timing, drug name, dose and indication.
Objective measurements of allergen and endotoxin exposure
We have also collected information about the environment in which the children have grown up, including the collection of dust samples from the home for detailed laboratory analysis. We collected dust samples by vacuuming a 1m2 area for 2 minutes in a standardised fashion using a dust sampler. The sampling head was loaded with a stainless steel mesh filter, to remove particles >300μm diameter, allowing fine dust to be collected onto a 5 μm pore size vinyl filter. Dust sample was transferred into pre-weighed petri dishes and coded. The filled petri dish was weighed to calculate the mass of fine dust collected and stored at 4oC until extraction.
Endotoxin content was measured by a kinetic limulus assay. All samples were assayed for content of major Dermatophagoides pteronyssinus allergen Der p 1 and for major cat allergen Fel d 1 using monoclonal antibody (mAb) based ELISAs and for major dog allergen Can f 1 using a monoclonal/polyclonal antibody-based ELISA. Der p 1 ELISA. The monoclonal antibodies were supplied by Indoor Biotechnologies, courtesy of Dr MD Chapman, University of Virginia, Charlottesville, USA.
Biological samples and genotyping
Biological samples (serum, plasma and urine) are stored on many of the children from multiple time points and allergen-specific IgE, IgG and IgG4s have been measured. DNA has been collected on most children (>1000 from blood or buccal swabs). We have completed whole genome genotyping using the Illumina 610 quad chip.
Manchester Primary Prevention Study
Nested within the Manchester Asthma and Allergy Study is a Manchester Primary Prevention Study which investigates whether a stringent environmental control and indoor allergen avoidance from pregnancy reduces the risk of asthma/allergies throughout the childhood. Children at high risk of asthma/allergies (who have both parent atopic), with no pets in the home at recruitment were randomized to stringent environmental control.
a) Prenatal (completed by the 16th week of pregnancy):
Parental bed (pillow, mattress and quilt) covered with mite-proof bedding through pregnancy and after delivery
Parents provided with a high filtration vacuum cleaner
Bed linen subjected to hot washing (55°C cycle) fortnightly
b) Infants bedroom:
At 36 weeks of pregnancy carpets were removed and replaced by vinyl floor
New cot mattress encased in mite allergen-proof material supplied
New carrycot mattress encased in mite allergen-proof material supplied
Any bed linen is subjected to hot washing (55°C cycle) fortnightly
Washable soft toy supplied.
c) Rest of the house:
Acarosan (benzyl benzoate) applied to carpets/sofas.