Investigating indicators and determinants of asthma in young adults.
BACKGROUND
In epidemiological studies on asthma determinants an extreme variability in results exists, probably due to different criteria utilised for defining of an asthma 'case' and for measuring determinants. We aimed to assess multiple indicators and multiple determinants of asthma in young adults by applying latent variable mixture models (LVMMs), a novel statistical modelling with hidden (or latent) variables.


METHODS
We consider the pooled data of 1103 subjects (aged 20-44 years) from the three Italian centres of the European Community Respiratory Health Survey (ECRHS 1), a standardised database. Underlying multiple asthma indicators (clinicians' diagnosis, self-report symptoms, respiratory trials) both a latent two-class of asthma syndrome, and three continuous latent variables (severity of diagnosed asthma, severity of asthma symptoms, and severity of respiratory function) were investigated.


RESULTS
Family history was the more relevant predictor of the two-class of asthma syndrome with a risk increase of about 60% per 1 relative with early life events (OR = 1.60, 95% CI: 1.30-1.97). Smoking, active and passive, are predictive for the indicators of severity of asthma symptoms. On average the risk increase of about 10% (OR = 1.10, 95%CI: 1.01-1.20) either per 1 source point of environmental tobacco smoke (ETS) or per 1 packet a day per 10 years. While, the risk of the indicators of both severity of asthma symptoms (OR = 1.59, 95%CI: 1.23-2.06) and severity of respiratory function (OR = 1.37, 95%CI: 1.03-1.82) increase in women compared to men, the risk of the indicators of severity of diagnosed asthma (OR = 0.57, 95%CI: 0.35-0.91) decreases.


CONCLUSIONS
Considering latent modelling perspective for formulating plausible hypotheses in asthma research, this study highlighted that the host (genetic) component measured as number of relatives with life-events of asthma and/or allergies seems to be the primary determinants of overall observed asthma indicators summarised by hidden two-class of asthma syndrome. Furthermore, a secondary (or trigger) role of smoking on the continuous latent variable of severity of asthma symptoms, and a gender reversal effect were suggested.
Grassi
Mario
M
Department of Health Sciences, Section of Medical Statistics & Epidemiology, University of Pavia, via Bassi, 21, Pavia, 27100, Italy. mario.grassi@unipv.it
Bugiani
Massimiliano
M
de Marco
Roberto
R
D000328:Adult; D001249:Asthma / Q000453:epidemiology / Q000209:etiology*; D005260:Female; D006801:Humans; D008297:Male; D015233:Models, Statistical; D012907:Smoking; D014028:Tobacco Smoke Pollution / Q000009:adverse effects
D014028:Tobacco Smoke Pollution