Known Risk Factors For Asthma Research Articles

Malaysian Society of Allergy and Immunology Consensus Statement on Sublingual Immunotherapy in Allergic Rhinitis.

Allergic rhinitis (AR) is an IgE-mediated inflammatory disease of the upper airway. AR affects the patients' quality of life, is a known risk factor for asthma and a socio-economic burden. Allergen-specific immunotherapy (AIT), comprising sublingual immunotherapy (SLIT) and subcutaneous immunotherapy (SCIT), involves administering increasing doses of the causative allergen to induce clinical and immunologic tolerance to the allergens. It is the only currently available treatment for AR that has been proven to induce disease-modifying effects (i.e., long-term remission of allergic symptoms or potential prevention of asthma and new sensitizations). Although AIT is conventionally recommended for patients who are non-responsive to symptom-relieving pharmacotherapy, it is presently recommended as a first-line treatment for patients with moderate to severe AR who prefer a treatment with the potential for long-term remission. In light of the relatively recent implementation of AIT in Malaysia, guidelines on its appropriate indication and application are important to attain optimal outcomes. This consensus statement was developed by an expert group formed by the Malaysian Society of Allergy and Immunology to provide evidence-based recommendations for the practice of AIT in Malaysia. Patient and product selection, choice of AIT, and strategy towards an effective treatment outcome in AIT are presented.

Long-term effect of asthma on the development of obesity among adults: an international cohort study, ECRHS

IntroductionObesity is a known risk factor for asthma. Although some evidence showed asthma causing obesity in children, the link between asthma and obesity has not been investigated in adults.MethodsWe used...

The Interplay Between Eczema and Breastfeeding Practices May Hide Breastfeeding’s Protective Effect on Childhood Asthma

Early allergic disease manifestations in infants may influence breastfeeding practices. In the current study, researchers sought to examine the relationship between breastfeeding duration and the development of asthma and allergic asthma phenotypes, stratified by a diagnosis of eczema during or after breastfeeding.Children who participated in the 6 year follow-up of the HealthNuts study, a population-based, longitudinal cohort study of allergic diseases in Australia.Children were enrolled between the ages of 11 and 15 months, and data regarding breastfeeding history, eczema diagnosis, environmental exposures, and family history of allergic disease were collected via questionnaire. At 6 years, information on wheeze, medication use, and parental report of physician-diagnosed asthma were obtained. Skin-prick testing to foods and aeroallergens at the age of 6 helped to stratify children with asthma into allergic and nonallergic phenotypes. From an original cohort of 5276 children, 3663 had completed questionnaires at 6 years, 3111 underwent skin testing, and 3632 had asthma data available for analysis. Children were characterized as never or ever breastfed. Of those breastfed, exclusive breastfeeding was categorized as never, <6 months, or >6 months. The overall duration of breastfeeding was treated as both a continuous (number of months) and categorical variable (<3 months, 3 to <6 months, 6 to <12 months, or >12 months).Children who did not participate in the full questionnaire at the age of 6 were more likely to be never breastfed, from a lower socioeconomic background, have one or both parents born outside of Australia, have no family history of allergic disease, and have had exposure to prenatal maternal or environmental smoking. Among children with asthma data, 96% were breastfed. At the age of 6, the prevalence of current asthma was 13%. Children with asthma were more likely to be male, have a parental history of asthma, have a family history of allergic disease, have been born preterm, have been born via cesarean delivery, and have been exposed to maternal smoking during pregnancy. Breastfeeding initiation was not associated with current asthma at the age of 6 years (adjusted odds ratio: 0.76) when compared with never breastfeeding. An increased duration of breastfeeding in children without eczema in infancy was associated with a reduced odds of asthma (per month increase; adjusted odds ratio: 0.98), which equates to a 0.86 reduced odds of asthma for a 6 month increase in breastfeeding. This association was not apparent in children who were diagnosed with eczema during breastfeeding.A longer duration of breastfeeding was associated with a reduced odds of asthma at the age pf 6 years among children without history of eczema in the first year. This association was masked before stratification of patients by history of eczema in infancy.Breastfeeding is known to be beneficial for improving many health outcomes. However, previous studies have not clearly demonstrated protective effects for breastfeeding on asthma. In the current study, a modest protective association was observed between an increased duration of breastfeeding and asthma but only among children who were not diagnosed with eczema in their first year. This association is complex because infantile eczema is a known risk factor for asthma and has also been shown to influence breastfeeding choices. Additional study is needed on the interplay between breastfeeding practices, early allergic manifestations, and the risk of subsequent allergic outcomes.

Predominance of Atopic Asthma in Patients with Severe or Difficult-to-Treat Asthma in the TENOR-II cohort

Atopy, the genetic propensity to produce immunoglobulin E (IgE) against common environmental allergens, is a known risk factor for asthma.1 In 2001, the TENOR I observational study (NCT00091767) was initiated to understand the natural history of disease in patients with severe or difficult-to-treat asthma.2 TENOR II was a multicenter, observational study conducted more than 10 years later using cross-sectional follow-up assessment of patients from TENOR I.2 As the “difficult-to-treat” asthma phenotype remains poorly defined, we sought to determine prevalence of atopy in TENOR II and describe demographic and clinical differences between patients with atopic and nonatopic asthma.

Impact of traffic-related air pollutants emission reduction policies on hospitalization by asthma, in Seoul and Incheon, Korea

Although the goals of most air-quality policies is to reduce direct emissions from the source points, it also aims to reduce health burden due to exacerbated environmental pollution. Therefore, assessing the impact of environmental policies on related health outcomes is important. In Korea, especially in Seoul and Incheon, interventions for reducing traffic-related air pollutants (TRAP) were aggressively implemented since 2007. TRAP is a known risk factor for asthma. In this study, we aimed to investigate whether the interventions had a beneficial impact on hospitalization by asthma.Hospital records for hospitalization by asthma in the study (Seoul and Incheon) and the reference population (Daejeon, Daegu, Busan, and Ulsan) were abstracted from the database in National Health Insurance Service during 2003 to 2011. A controlled interrupted time series design (C-ITS) was adopted to assess the impact of air pollutants emission reduction policies on hospitalization by asthma. Long-term background trends were adjusted using the trends of reference cities. Various sensitivity analyses, including simple-ITS, and C-ITS with false-intervention and with simulated PM10 concentration when there was no intervention, were conducted to give a robustness of our study result.Emissions from traffic-related air pollutants were significantly reduced after 2007. Estimated numbers of prevented hospitalization for asthma in Seoul were 10,377 (14.1%) and 6,011 (8.7%) depending on the reference population (Daejeon and Daegu). For Incheon, estimated numbers of prevented hospitalization for asthma were 3,207 (11.7%) and 2,470 (9.2%) depending on the reference population (Busan and Ulsan). Potential beneficial effects of the interventions on asthma were also found in the sensitivity analysis. Our study provides supportive evidence for potential beneficial effects of interventions for reducing TRAP on hospitalization for asthma in Seoul and Incheon. More studies are needed to determine the impact of such environmental policy implementation on other diseases associated with air pollutants in Korea.

Being overweight in childhood, puberty, or early adulthood: Changing asthma risk in the next generation?

Overweight status and asthma have increased during the last decades. Being overweight is a known risk factor for asthma, but it is not known whether it might also increase asthma risk in the next generation. We aimed to examine whether parents being overweight in childhood, adolescence, or adulthood is associated with asthma in their offspring. We included 6347 adult offspring (age, 18-52years) investigated in the Respiratory Health in Northern Europe, Spain and Australia (RHINESSA) multigeneration study of 2044 fathers and 2549 mothers (age, 37-66years) investigated in the European Community Respiratory Health Survey (ECRHS) study. Associations of parental overweight status at age 8years, puberty, and age 30years with offspring's childhood overweight status (potential mediator) and offspring's asthma with or without nasal allergies (outcomes) was analyzed by using 2-level logistic regression and 2-level multinomial logistic regression, respectively. Counterfactual-based mediation analysis was performed to establish whether observed associations were direct or indirect effects mediated through the offspring's own overweight status. We found statistically significant associations between both fathers' and mothers' childhood overweight status and offspring's childhood overweight status (odds ratio, 2.23 [95% CI, 1.45-3.42] and 2.45 [95% CI, 1.86-3.22], respectively). We also found a statistically significant effect of fathers' onset of being overweight in puberty on offspring's asthma without nasal allergies (relative risk ratio, 2.31 [95% CI, 1.23-4.33]). This effect was direct and not mediated through the offspring's own overweight status. No effect on offspring's asthma with nasal allergies was found. Our findings suggest that metabolic factors long before conception can increase asthma risk and that male puberty is a time window of particular importance for offspring's health.

Impact of Obesity on Asthma Morbidity During a Hospitalization.

Asthma and obesity are 2 common pediatric problems. Obesity is a known risk factor for asthma, and obese children with asthma have higher disease burden. However, little is known on how obesity in urban minority children, mainly Hispanic and African American children, impacts morbidity during pediatric asthma hospitalizations. A retrospective chart review was conducted on children and adolescents age 2 to 18 years hospitalized at the Children's Hospital at Montefiore for an acute asthma exacerbation. We elucidated the association of overweight or obese status with severity of the exacerbation, quantified by length of stay (LOS) and need for intensive care management. Multivariate analysis was conducted to identify independent predictors of LOS. A total of 975 children met the inclusion criteria, of whom 55% were normal weight and 45% were overweight or obese. Sixty percent were Hispanic, and 37% were African American. The overall average LOS was 2.57 days (range: 0.67-12.92). Overweight or obese status was associated with a higher asthma severity at baseline (P = .021). Overweight or obese children had a longer average LOS compared with normal weight children (2.75 vs 2.39 days; P < .01) with more PICU stays (P = .006), even after adjustment for higher baseline asthma severity. The severity of the exacerbation did not differ by ethnicity. Obesity in children hospitalized for asthma is associated with more severe asthma exacerbations, longer LOS, and increased use of PICU level care, independent of their higher baseline disease severity and ethnicity.

Severe asthma in obese patients: Improvement of lung function after treatment with omalizumab

IntroductionAsthma and obesity have a considerable impact on public health and their prevalence is increasing. Obesity is a known risk factor for asthma and can make it more difficult to control. Omalizumab is recommended in patients with severe allergic persistent asthma. The aim of this study was to assess the impact of omalizumab treatment in obese asthmatic patients with poorly controlled severe persistent asthma. MethodologyA non-interventional, prospective study was conducted, in an outpatient asthma clinic. All patients with severe asthma who started treatment with omalizumab were included and followed over 12 months. The study population was divided into two groups (obese and non-obese) for statistical analysis (descriptive and comparative analysis). ResultsThirty-two patients (19 obese) were followed. After 12 months of omalizumab treatment, there was a statistically significant improvement in body mass index, number of exacerbations in the previous year, rescue medication, disease control and lung function, in the whole population. At the end of the study obese patients had a significantly better lung function (FEV1) than non-obese. DiscussionAs described in the literature, there was a significant reduction in the number of exacerbations in the previous year, rescue medication and better disease control, in the whole population. In relation to lung function, about which published data are inconsistent, treatment with omalizumab significantly improved it in obese patients. ConclusionOur study showed that omalizumab significantly improved asthma control, reduced rescue medication and asthma exacerbations in all the population; and for the first time showed that obese patients achieved significantly improved lung function.

Usefulness of asthma predictive index in ascertaining asthma status of children using medical records: An explorative study.

Frequent wheezing in original asthma predictive index (API) was defined by parental report of recurrent wheezing within 1year during the first 3years of life. The nature of frequent wheezing in children, particularly aged over 3years, has not been studied. We aimed to assess the frequency and interval of wheezing to define frequent wheezing in ascertaining asthma for children using medical records. Among children who participated in a previous study (n=427), all wheezing episodes documented in medical records were collected for children who had ≥2 wheezing episodes PLUS met one major criterion or two minor criteria of API. We compared the distribution of known risk factors for asthma between subjects having two consecutive wheezing episodes with shorter interval (≤1year) compared to those with longer interval (1 to 3years). A total of 62 children met API at median age of 2.3years. During follow-up period (median age: 11.3years), a total of 198 wheezing episodes were observed. 81% of wheezing intervals were within 3years from the earlier wheezing episode, including 60% within 1year. Children who met API based on 1-year interval (n=40) vs 1- to 3-year interval (n=13) appeared to be similar in regard to the known risk factors for asthma. Our exploratory study finding suggests that children who had frequent wheezing episodes with longer interval (<3years) need to be considered to be determined as asthma cases when API is applied to retrospective medical records. Prospective studies with a larger sample size need to replicate this finding.

Natural Language Processing for Asthma Ascertainment in Different Practice Settings

We developed and validated NLP-PAC, a natural language processing (NLP) algorithm based on predetermined asthma criteria (PAC) for asthma ascertainment using electronic health records at Mayo Clinic. To adapt NLP-PAC in a different health care setting, Sanford Children Hospital, by assessing its external validity. The study was designed as a retrospective cohort study that used a random sample of 2011-2012 Sanford Birth cohort (n= 595). Manual chart review was performed on the cohort for asthma ascertainment on the basis of the PAC. We then used half of the cohort as a training cohort (n= 298) and the other half as a blind test cohort to evaluate the adapted NLP-PAC algorithm. Association of known asthma-related risk factors with the Sanford-NLP algorithm-driven asthma ascertainment was tested. Among the eligible test cohort (n= 297), 160 (53%) were males, 268 (90%) white, and the median age was 2.3 years (range, 1.5-3.1 years). NLP-PAC, after adaptation, and the human abstractor identified 74 (25%) and 72 (24%) subjects, respectively, with 66 subjects identified by both approaches. Sensitivity, specificity, positive predictive value, and negative predictive value for the NLP algorithm in predicting asthma status were 92%, 96%, 89%, and 97%, respectively. The known risk factors for asthma identified by NLP (eg, smoking history) were similar to the ones identified by manual chart review. Successful implementation of NLP-PAC for asthma ascertainment in 2 different practice settings demonstrates the feasibility of automated asthma ascertainment leveraging electronic health record data with a potential to enable large-scale, multisite asthma studies to improve asthmacare and research.

Progression from Asthma to Chronic Obstructive Pulmonary Disease. Is Air Pollution a Risk Factor?

Individuals with asthma-chronic obstructive pulmonary disease (COPD) overlap syndrome (ACOS), have more rapid decline in lung function, more frequent exacerbations, and poorer quality of life than those with asthma or COPD alone. Air pollution exposure is a known risk factor for asthma and COPD; however, its role in ACOS is not as well understood. To determine if individuals with asthma exposed to higher levels of air pollution have an increased risk of ACOS. Individuals who resided in Ontario, Canada, aged 18 years or older in 1996 with incident asthma between 1996 and 2009 who participated in the Canadian Community Health Survey were identified and followed until 2014 to determine the development of ACOS. Data on exposures to fine particulate matter (PM2.5) and ozone (O3) were obtained from fixed monitoring sites. Associations between air pollutants and ACOS were evaluated using Cox regression models. Of the 6,040 adults with incident asthma who completed the Canadian Community Health Survey, 630 were identified as ACOS cases. Compared with those without ACOS, the ACOS population had later onset of asthma, higher proportion of mortality, and more frequent emergency department visits before COPD diagnosis. The adjusted hazard ratios of ACOS and cumulative exposures to PM2.5 (per 10 μg/m(3)) and O3 (per 10 ppb) were 2.78 (95% confidence interval, 1.62-4.78) and 1.31 (95% confidence interval, 0.71-2.39), respectively. Individuals exposed to higher levels of air pollution had nearly threefold greater odds of developing ACOS. Minimizing exposure to high levels of air pollution may decrease the risk of ACOS.

Job strain, bullying and violence at work and asthma in Peruvian cleaners—a cross-sectional analysis

Objectives: An increased asthma prevalence was found in cleaners. Many of them work in precarious employment conditions, potentially leading to stress, a known risk factor for asthma. We aimed to analyze whether asthma in cleaners might partly be explained by psychosocial working conditions. Methods: The study population of this cross-sectional study included 199 cleaners employed at regional public health services in Puno Province (Peru). They were compared to 79 unexposed workers from Lima, Peru (response 83%). Both groups answered the short version of the European Working Condition Survey and a modified version of the European Community Respiratory Health screening questionnaire. After multiple imputation, the association between psychosocial working conditions and asthma (wheeze without cold or use of asthma medication) was assessed. Results: The 12-months prevalence of asthma was 22% among cleaners versus 5% among unexposed workers (pChi2 = .001). Cleaners were more likely than unexposed workers to work with temporary or sub-contracts, have a high employment insecurity, high strain working conditions and low social support (all pChi2 < .05). Twenty-six percent vs. 10% reported a high bullying score; 39% vs. 8% had experienced violence at work (both pChi2 < .001). High bullying score (adjusted Odds Ratio 5.6; 95% Confidence Interval 1.5–21.4) and violence (2.4; 1.1–5.4) were the main predictors of asthma. Taking these factors into account, being a cleaner was not statistically significantly associated with the outcome (3.5; 0.9–13.8). Conclusions: Poor psychosocial working conditions of cleaners may partly explain the high prevalence of asthma. The underlying mechanism might be a stress-induced inflammatory immune response.

IgE responses to Ascaris and mite tropomyosins are risk factors for asthma.

The relationship between helminthiases and allergy is a matter of considerable interest and research. In the tropics, house dust mite exposure, a known risk factor for asthma, is frequently concurrent with helminth infections. It remains to be defined whether infection with the common roundworm Ascaris or its bystander immunological effects influence the prevalence and pathogenesis of asthma independently of mite sensitization. To investigate the relationship between the IgE responses to Ascaris and its purified allergens and the risk of asthma in a tropical country. A nested case-control study was performed in 356 subjects who reported current and past asthma symptoms (asthmatics) and 435 controls that had never experienced such symptoms. They were tested for serum levels of total IgE and specific IgE to Ascaris extract, Asc s 1 (ABA-1), Asc l 3 (tropomyosin) and GST (glutathione transferase). In addition, specific IgE to Dermatophagoides pteronyssinus, Blomia tropicalis and their tropomyosins Der p 10 and Blo t 10 was measured. Sensitization was defined as a positive specific IgE result to any extract or recombinant allergen. Sensitization to Ascaris and D. pteronyssinus was independently associated with asthma after adjustment for age, gender, socio-economic stratum, city and other IgE levels (adjusted ORs: 2.17; 95% CI 1.37-3.42 and 2.46; 95% CI 1.54-3.92), respectively. There was also a significant association with sensitization to the highly allergenic and cross-reactive tropomyosins Asc l 3, Blo t 10 and Der p10 (aORs: 1.76; 95% CI 1.21-2.57, 1.64; 95% CI 1.14-2.35 and 1.51; 95% CI 1.02-2.24), respectively. IgE responses to Ascaris are associated with asthma symptoms in a population living in the tropics. Sensitization to the cross-reactive Ascaris and mite tropomyosins partially underlies this finding. These results have potential relevance in asthma diagnosis and management.

Is the Effect of Prenatal Paracetamol Exposure on Wheezing in Preschool Children Modified by Asthma in the Mother?

Background: There seems to be an association between paracetamol consumption during late pregnancy and the prevalence of wheezing in infancy and childhood. The aim of the present study is to determine whether the aforementioned association is modified by the presence of asthma in the mother. Methods: A total of 1,741 children aged 3–5 years from an epidemiological survey performed in the province of Murcia (Spain) were included in the analysis. Data on paracetamol consumption (never, at least once during pregnancy or at least once per month during pregnancy), wheezing symptoms in the offspring (according to the International Study of Asthma and Allergies in Childhood protocol) and the presence of asthma in the mother, together with other known risk factors for asthma, were obtained by means of a questionnaire. Results: The mean age of the children was 4.08 ± 0.8 years and 51.1% were males. The overall prevalence of current wheezing was 20.2%. The frequency of paracetamol usage was similar among asthmatic and non-asthmatic mothers, and only a small proportion of them took this drug at least once a month (13.8% of asthmatics and 11.0% of non-asthmatics). Compared to the mothers who never took paracetamol, there was a significant association between the mother having taken paracetamol at least once per month during pregnancy and the offspring suffering from wheezing at preschool age, but only among non-asthmatic mothers (odds ratio 1.94, 95% confidence interval 1.34–2.79 vs. odds ratio 1.05, 95% confidence interval 0.21–5.08). This association was maintained after controlling for potential confounders (odds ratio 1.74, 95% confidence interval 1.15–2.61). Conclusions: The frequent usage of paracetamol during pregnancy is associated with the prevalence of wheezing in offspring during preschool years. Asthma in the mother might modify this association.

Family History of Asthma and Atopy: In-depth Analyses of the Impact on Asthma and Wheeze in 7- to 8-Year-Old Children

Development of asthma in children is influenced by interactions between genetic and environmental factors. It is unclear whether paternal or maternal histories of disease confer different risks. Previous population-based studies have not stratified analyses by child gender and sensitization status. Our aim was to study in detail the hereditary component of childhood asthma. A population-based cohort of 3430 (97% of invited) 7- to 8-year-old school children participated in an expanded International Study of Asthma and Allergy in Childhood survey, and two thirds were skin-prick tested. Heredity was defined as a family history of (1) asthma and (2) atopy (allergic rhinitis or eczema). Multivariate analyses corrected for known risk factors for asthma. At ages 7 to 8, prevalence of asthma was 5.3% among the children and 9.0% among the parents. In children without parental asthma or parental atopy, the prevalence of asthma was 2.8%. Corrected for parental asthma, parental atopy was a weak but significant risk factor. There were minor differences in the impact of parental disease between sensitized and nonsensitized children and between boys and girls. As risk factors for childhood asthma, there were major differences between parental asthma and parental atopy. Sibling asthma was only a marker of parental disease. Interactions between parental disease and the child's allergic sensitization or gender were not statistically significant. Asthma in both parents conferred a multiplicative risk, whereas the effect of parental atopy was additive, however limited. Asthma and atopy, despite their causal relationship, are separate entities and could be inherited differently. This large, population-based, and well-characterized cohort study does not confirm parent-of-origin effects found in previous studies.

Update on gastroesophageal reflux disease and asthma in children

About 60% of children with asthma have concomitant gastroesophageal reflux disease (GERD). The exact role of GERD in asthma is speculative, but aggressive treatment of GERD results in clinical improvement of asthma without a consistent improvement in pulmonary functions. Evaluation of GERD in children with persistent, difficult-to-treat asthma should be considered, especially in those with no known risk factors for asthma.

Familial Risk of Asthma Among Adolescents and Their Relatives in Taiwan

Although family studies have established that asthma has a hereditary basis, little evidence has been presented about the family risk of simple asthma (AS or nonatopic asthma) and asthma with other atopic diseases (AWAD or atopic asthma) after adjusting for potential risk factors. In this study, data were collected on demographic variables and a wide range of known risk factors for asthma. Study participants were asthmatic adolescents and controls, and their relatives. The role of a familial history of asthma and atopic diseases in predicting asthma risk among asthmatic adolescents and their relatives was evaluated in a population-based family study conducted in southern Taiwan. Asthma risk factor data were collected through telephone interviews with students' parents for 207 asthmatic adolescents 11–16 years of age, their 1600 relatives, and 207 nonasthmatic adolescents in the control group and their 1638 relatives. The results show (after adjusting potential confounders) that a family history of asthma is highly associated with asthma in adolescents. Having two or more family members with asthma was associated with a 3.4-fold (95% confidence interval [CI]=1.0–12.0) increased risk of asthma among adolescents. Logistic regression was used to assess the effects of having an asthmatic relative and the effect of atopic diseases among relatives of cases. Having a family history of asthma and other atopic conditions, such as rhinitis and atopic dermatitis (adjusted odds ratio [AOR]=3.64, 95% CI=2.29–5.74 and AOR=1.94, 95% CI=1.53–2.46, respectively), was found to be a significant predictor of asthma in children. Along with a history of allergic rhinitis or atopic dermatitis, familial risks of asthma occurring in adolescents with and without other atopic diseases will be analyzed separately. A critical finding was the significant difference in a risk of asthma and atopic diseases among the relatives of asthma cases with atopic diseases and controls. However, for relatives of asthma cases without atopic diseases compared to control probands, AORs were highly significant for family history of asthma, but not for the family history of atopic diseases. These findings suggest that both forms of asthma may be hereditary, but there are differences in their modes of inheritance. Atopic status itself did not predispose a child to AS. A concomitant inheritance of a predisposition to asthma and atopic condition for AWAD cases was suggested.

Maternal smoking and childhood asthma.

The role of maternal smoking as a causal factor for the incidence of childhood asthma is still not clearly established. It was investigated among 3- and 4-year-old-child incident cases confirmed by a 6-year follow-up (n = 294) and cases who no longer had symptoms after diagnosis (n = 110). The study took place in Montréal, Canada, between 1988 and 1997. Persistent and transient cases were compared with their respective controls from the original case-control study of incidence. The odds ratio for heavy maternal smoking adjusted for known risk factors for asthma was 3.84 (95% confidence interval: 1.68, 8.76) among persistent cases and close to one among transient cases.