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 Table of Contents  
ORIGINAL ARTICLE
Year : 2017  |  Volume : 1  |  Issue : 1  |  Page : 11-16

The predictive factors in preschool wheezers for subsequent asthma hospitalization after the age of 6 years


Department of Paediatrics, Kwong Wah Hospital, Hong Kong SAR, China

Date of Web Publication14-Mar-2017

Correspondence Address:
Daniel Kwok-Keung Ng
Department of Paediatrics, Kwong Wah Hospital, 25, Waterloo Road, Hong Kong SAR
China
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/prcm.prcm_15_16

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  Abstract 

Background: Preschool children with wheeze may develop asthma later at school age. Positive skin prick test (SPT) to common aeroallergens in preschool wheezers may be associated with a higher chance of developing asthma at school age. Methods: All patients with SPT performed for the indication of preschool wheeze, i.e., before the age of 6 years, were included in the study from 1999 to 2011. Outcome measures including asthmatic attack requiring emergency hospitalization and the need for asthma controller prescription after the age of 6 years were retrieved from the hospital database. Potential risk factors including gender, family history of asthma, blood eosinophilia, environmental tobacco exposure, personal eczema, and allergic rhinitis were also retrieved for analysis. Multiple logistic regression was performed to identify independent risk factors. Results: Altogether, 463 children were included for analysis with mean age at SPT of 3.1 ± 1.36 years and 64.6% were male. Positive SPT results were obtained in 60.5% of patients. For preschool children with wheeze, female gender (odds ratio [OR] = 1.90, 95% confidence interval [CI]: 1.04–3.46, P = 0.036), positive SPT (OR = 2.96, 95% CI: 1.40–6.24, P = 0.004), and late-onset preschool wheeze hospitalization (OR = 2.82, 95% CI: 1.42–5.61, P = 0.003) were associated with a higher chance of asthmatic hospitalization after the age of 6 years. Allergic rhinitis (OR = 4.58, 95% CI: 2.16–9.71, P < 0.001) and family history of asthma (OR = 1.82, 95% CI: 1.09–3.02, P = 0.022) were associated with higher chance for asthma controller prescription. Conclusion: For preschool wheeze, female gender, positive SPT, and late-onset preschool wheeze index are associated with a higher chance of asthmatic hospitalization after the age of 6 years while allergic rhinitis and family history of asthma are associated with a higher chance for asthma controller prescription after the age of 6 years.

Keywords: Allergens, asthma, child


How to cite this article:
Yu PT, Chan JY, Poon F, Lee RS, Leung SY, Ng JP, Siu KK, Yip AY, Kwok KL, Chan EY, Wong JC, Ng DK. The predictive factors in preschool wheezers for subsequent asthma hospitalization after the age of 6 years. Pediatr Respirol Crit Care Med 2017;1:11-6

How to cite this URL:
Yu PT, Chan JY, Poon F, Lee RS, Leung SY, Ng JP, Siu KK, Yip AY, Kwok KL, Chan EY, Wong JC, Ng DK. The predictive factors in preschool wheezers for subsequent asthma hospitalization after the age of 6 years. Pediatr Respirol Crit Care Med [serial online] 2017 [cited 2017 Aug 23];1:11-6. Available from: http://www.prccm.org/text.asp?2017/1/1/11/201978


  Introduction Top


Preschool wheeze has been reported to occur in 30% of children within the first 3 years of life and up to 50% of children before the age of 6 years.[1],[2] In Hong Kong, it was reported that acute wheeze accounted for 10% of all emergency admissions to public hospitals.[3] Martinez et al. and Brooke et al. suggested that about 40% of children with preschool wheeze would develop persistent wheeze after the age of 6 years.[1],[4] Early allergic sensitization was one of the identified risk factors for subsequent asthma development among preschool wheezers.[5],[6],[7] Skin prick test (SPT) is an easily available, safe, and simple test for allergic sensitization. Kurukulaaratchy et al. had shown that a positive SPT was one of the risk factors to predict persistent wheeze in children who had wheeze during early life.[8] Sensitization to aeroallergen was included in the Asthma Predictive Index developed from the Tucson cohort.[9] However, similar data were not available for Asian children. In the current study, we aimed to investigate whether SPT performed in preschool wheezers could predict asthma hospitalization and the need for asthma controller medication after the age of 6 years.


  Methods Top


Study population

This was a retrospective observational study targeting preschool wheezers who had SPTs performed in the Department of Paediatrics, Kwong Wah Hospital, from January 1999 to December 2011. During the study period, patients with preschool wheeze, who were either seen in the outpatient clinics or hospitalized, were offered SPT to check whether the wheeze was recurrent or severe. The inclusion criteria of the study included: (1) SPTs performed for the investigation of preschool wheeze in children aged <6 years and (2) participants completed at least 2-year follow-up in the pediatric specialist outpatient clinic after they turned 6-year-old. In the authors' department, SPTs were arranged for patients with two or more wheezes or wheezes requiring hospitalization. The exclusion criteria included (1) invalid SPTs, such as positive control test that was negative; (2) SPT performed for other or undocumented indications (e.g., suspected cow milk protein allergy, food allergy, recurrent urticarial, etc.); and (3) patients with chronic lung disease (e.g., bronchopulmonary dysplasia associated with prematurity, bronchiectasis, bronchiolitis obliterans, etc.) [Figure 1]. A flowchart of the study cohort is shown in [Figure 2].
Figure 1: Flow chart for case recruitment.

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Figure 2: Flow chart for hospitalization of preschool wheezers.

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Data retrieval

Medical records of all the included patients were retrieved from the Hong Kong Hospital Authority (HKHA) computer medical systems. Data on the incidence of wheeze requiring emergency admissions to public hospitals under HKHA before and after the age of 6 years and potential confounding factors including gender, family history of asthma in the first-degree relatives, history of allergic rhinitis and eczema, environmental tobacco exposure, and peripheral blood eosinophilia (≥4%) were obtained. All electronic data were kept in encrypted spreadsheet and stored in a password-protected computer. Hard copies of records were stored in a locked cabinet. Wheeze without cold was not included because nasopharyngeal aspirates for respiratory virus were not routinely performed for all children who were admitted for wheeze in our hospital. Data on asthma controller prescription as listed in Appendix 1, prescribed at the age of 6 years or older, were retrieved from the hospital Clinical Data Analysis and Reporting System. For those who did not have regular pediatric specialist outpatient follow-up at the age of 6 years or above, a phone follow-up with standardized questions concerning asthma controller prescription by private doctors was conducted by one of the authors (PTY).



Outcome measures

The primary outcome was emergency asthma admissions to public hospitals after the age of 6 years. The secondary outcome was prescription of asthma controller medications after the age of 6 years.

Skin prick test

SPTs were performed according to the guideline described in the allergy diagnostic testing by the American Academy of Allergy, Asthma, and Immunology (AAAAI) and the ACAAI.[10] Patients were asked to withhold medications such as antihistamine, oral/topical steroid, and herbal medicine, 1 week before the test. The tests were performed by trained medical staff. The ventral part of forearm was pricked gently after the relevant allergens were placed onto the skin with a lancet or Stallerpoint ®, used since January 2010. In addition to a positive control (histamine 1 mg/ml) and a negative control (saline), six aeroallergens were tested, including house dust mites (Dermatophagoides farinae, Dermatophagoides pteronyssinus), cat, dog, grass, and feather mix, which are the common aeroallergens in Hong Kong.[11],[12] The results were interpreted 15 min later. The wheal size was measured as the summation of the longest transverse line and the corresponding longest perpendicular line divided by a factor of 2.

Definitions

SPT was defined as positive for an aeroallergen if the wheal size was 3 mm or greater than the negative control. SPT positivity was defined if SPT was positive for at least one tested aeroallergen.

Wheeze was classified as early-onset preschool wheezer (defined as the first wheeze before the age of 2 years) and late-onset preschool wheezer (defined as the first wheeze between the age of 2 years and 6 years).

Statistical analysis

All statistical analyses were performed with IBM SPSS Statistics for Windows, Version 22.0. (IBM Corp. in Armonk, NY, USA). The relationship between SPT positivity and emergency asthma admission/asthma controller prescription after the age of 6 years was investigated using Pearson's Chi-squared test. For continuous variables, normality was tested by Shapiro–Wilk test. Wilcoxon rank-sum test with continuity correction was used if continuous variables were not normally distributed. Univariate analysis was conducted to identify the potential risk factors for emergency asthma admission and asthma controller prescription after the age of 6 years. Multivariate logistic regression analysis was performed to identify the independent risk factors. The variables with P < 0.2 were put into the final regression model.


  Results Top


Patient characteristics

A total of 791 SPTs were done during the study period. Altogether 463 children were selected to be included in the study cohort [Figure 1], while 299 (64.6%) of them were male. Mean age at SPT was 3.1 ± 1.36 years. Majority were late preschool wheezers (n = 321, 69.3%) while 142 (30.7%) were early preschool wheezers.

Summary of skin prick test results

Among the 463 patients, 280 (60.5%) had positive SPT and 183 (39.5%) had negative results. Majority of the patients were sensitized to D. pteronyssinus (n = 266, 95%) and D. farinae (n = 245, 87.5%). Only a small proportion of children were sensitized to cat, dog, feather mix, or grass [Table 1].
Table 1: Results of skin prick tests for different aeroallergens

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Risk factors associated with emergency asthma admission after the age of 6 years

Univariate analysis showed that gender, SPT positivity, environmental tobacco exposure, eosinophilia, early preschool wheeze admission index per year (age <2 years), late preschool wheeze admission per year (age 2–<6 years), wheeze admission before the age of 6 years were the potential risk factors for asthmatic attack requiring emergency hospital admission after the age of 6 years [Table 2]. After adjusting for the potential confounding factors in the multivariate logistic regression analysis, it was found that independent risk factors included female gender (odds ratio [OR]: 1.90, confidence interval [CI]: 1.04–3.46, P = 0.036), SPT positivity (OR: 2.96, CI: 1.40–6.24, P = 0.004), and late preschool wheeze admission index (OR: 2.82, CI: 1.42–5.61, P = 0.003) [Table 3]. Using the aforesaid model, the probability of asthma admission after the age of 6 years will be as follows:
Table 2: Univariate logistic regression analysis on the risk factors contributing to emergency asthma admission after the age of 6 years

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Table 3: Multivariable logistic regression analysis on the risk factors contributing to emergency asthma admission after the age of 6 years

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*Prediction Index A = Exp (−3.1 + 0.5 × female gender + 1.0 × SPT positivity + 1.4 × late preschool wheeze admission per year).

Using the above model, the OR of future asthma admission comparing children with various risk factors can be calculated. For instance, a child with female gender, SPT positivity, and a late preschool wheeze admission index of 1 will be almost 11 times more likely to be admitted for asthma after the age of 6 years than a child with male gender, SPT negativity, and a late preschool wheeze admission index of 0 [Appendix 2].



Risk factors associated with the prescription of asthma controller medications after the age of 6 years

Univariate analysis showed that gender, allergic rhinitis, family history of asthma, eosinophilia, SPT positivity, and late preschool wheeze admission were the potential risk factors for asthma controller prescriptions after 6 years of age [Table 4]. After adjusting for the potential confounding factors in the multivariate logistic regression analysis, it was found that independent risk factors were allergic rhinitis (OR: 4.58, CI: 2.16–9.71) and family history of asthma (OR: 1.82, CI: 1.09–3.02) [Table 5]. Using the aforesaid model, the probability of requiring asthma controller prescription after the age of 6 years will be:
Table 4: Univariate logistic regression analysis for prescription of asthma controller after the age of 6 years

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Table 5: Multivariable logistic regression analysis for prescription of asthma controller after the age of 6 years

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*Prediction index C = Exp (−2.8 + 0.6 × family history of asthma + 1.5 × allergic rhinitis)

Using the above model, the OR of prescription of asthma controller comparing children with various risk factors can be estimated. For instance, a child with allergic rhinitis and family history of asthma will be nearly 6 times more likely to be prescribed with asthma controller after the age of 6 years than a child without allergic rhinitis and family history of asthma [Appendix 3].




  Discussion Top


Early life allergic sensitization was well known to be a risk factor for developing subsequent asthma in later childhood.[6],[7] SPT is an easily available tool for identifying sensitization in young children. In the present study, our results suggested that SPT positivity may have a prognostic role in identifying those preschool wheezers who may have a higher chance to develop subsequent asthmatic attack requiring emergency hospital admission after the age of 6 years. Emergency hospital admission was a surrogate marker for a relatively severe asthmatic attack after the age of 6 years. Previous studies demonstrated the association between SPT positivity and wheeze persistency after preschool age.[7],[8],[9],[13] Kurukulaaratchy et al.[8] suggested that recurrent chest infections at 2 years old, family history of asthma, SPT positivity at 4 years old, and the absence of nasal symptoms at 1 year old were the four risk factors predicting the persistence of early life wheezing in later childhood. In the multivariate logistic regression model, female gender, SPT positivity, and late preschool wheeze admission index were the significant risk factors for asthma hospitalization after the age of 6 years. Female gender as a significant risk factor for asthma admission beyond the age of 6 years was consistent with the fact that females have lower specific airway resistance for the first 2 years of life.[14],[15] Therefore, girls, who wheezed despite their larger airway, were more likely to have asthma than boys who wheezed because of their smaller airway, hence more likely to outgrow it with time as the lower airway grows rapidly in the first 2 years of life.[15] Those with allergic rhinitis and family history of asthma were more likely to require asthma controller medication beyond the age of 6 years.

This study has several limitations. As it was a retrospective study, data retrieved from the hospital's clinical management system were not as comprehensive and complete as a prospective study using a standardized questionnaire. Potential confounding factor concerning concurrent viral infection was not included due to practical difficulties. In the present study, our primary outcome was based on data in emergency asthma admission to public hospitals only. Those patients with asthmatic attack who were admitted to private hospitals would have been missed even though HKHA accounted for 80.3% of the total inpatient service in Hong Kong.[16] Therefore, the association between SPT positivity and subsequent asthmatic attack requiring hospitalization may have been underestimated.

Regarding generalizability, SPTs were arranged for patients with two or more wheezes or a moderate-to-severe wheeze requiring hospitalization. Therefore, the findings would be more applicable to those preschool wheezers with more frequent or severe wheeze.


  Conclusion Top


The current study shows that female gender, SPT positivity, and number of preschool wheeze admissions after the age of 2 years predict asthma hospitalization after the age of 6 years. Furthermore, those with allergic rhinitis and family history of asthma are more likely to require asthma controller medication beyond the age of 6 years.

Acknowledgment

This work was supported by the Tung Wah Group of Hospitals Research Fund 2014/2015.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

1.
Martinez FD, Wright AL, Taussig LM, Holberg CJ, Halonen M, Morgan WJ. Asthma and wheezing in the first six years of life. The Group Health Medical Associates. N Engl J Med 1995;332:133-8.  Back to cited text no. 1
    
2.
Bisgaard H, Szefler S. Prevalence of asthma-like symptoms in young children. Pediatr Pulmonol 2007;42:723-8.  Back to cited text no. 2
    
3.
Chiu W, Lee LP, Ng DK, Lau TK, Lam P, Chan JY. Consensus report on Management of Wheezing in Preschool Children, Hong Kong Society of Paediatric Respirology. J Paediatr Respirol Crit Care 2011;7:4.  Back to cited text no. 3
    
4.
Brooke AM, Lambert PC, Burton PR, Clarke C, Luyt DK, Simpson H. The natural history of respiratory symptoms in preschool children. Am J Respir Crit Care Med 1995;152(6 Pt 1):1872-8.  Back to cited text no. 4
    
5.
Pescatore AM, Dogaru CM, Duembgen L, Silverman M, Gaillard EA, Spycher BD, et al. A simple asthma prediction tool for preschool children with wheeze or cough. J Allergy Clin Immunol 2014;133:111-8.e1-13.  Back to cited text no. 5
    
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Sonnappa S. Preschool wheeze: Phenotype and beyond. Pediatr Health 2010;4:267-75.  Back to cited text no. 6
    
7.
Lowe AJ, Hosking CS, Bennett CM, Carlin JB, Abramson MJ, Hill DJ, et al. Skin prick test can identify eczematous infants at risk of asthma and allergic rhinitis. Clin Exp Allergy 2007;37:1624-31.  Back to cited text no. 7
    
8.
Kurukulaaratchy RJ, Matthews S, Holgate ST, Arshad SH. Predicting persistent disease among children who wheeze during early life. Eur Respir J 2003;22:767-71.  Back to cited text no. 8
    
9.
Castro-Rodríguez JA, Holberg CJ, Wright AL, Martinez FD. A clinical index to define risk of asthma in young children with recurrent wheezing. Am J Respir Crit Care Med 2000;162(4 Pt 1):1403-6.  Back to cited text no. 9
    
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Bernstein IL, Li JT, Bernstein DI, Hamilton R, Spector SL, Tan R, et al. Allergy diagnostic testing: An updated practice parameter. Ann Allergy Asthma Immunol 2008;100(3 Suppl 3):S1-148.  Back to cited text no. 10
    
11.
Chow PY. A retrospective review of skin prick test results in children with atopic diseases. J Paediatr Respirol Crit Care (JPRCC) 2012;8:4-10.  Back to cited text no. 11
    
12.
Leung TF, Li AM, Ha G. Allergen sensitisation in asthmatic children: Consecutive case series. Hong Kong Med J 2000;6:355-60.  Back to cited text no. 12
    
13.
Illi S, von Mutius E, Lau S, Niggemann B, Grüber C, Wahn U; Multicentre Allergy Study (MAS) group. Perennial allergen sensitisation early in life and chronic asthma in children: A birth cohort study. Lancet 2006;368:763-70.  Back to cited text no. 13
    
14.
Doershuk CF, Fisher BJ, Matthews LW. Specific airway resistance from the perinatal period into adulthood. Alterations in childhood pulmonary disease. Am Rev Respir Dis 1974;109:452-7.  Back to cited text no. 14
    
15.
Thurlbeck WM. Postnatal human lung growth. Thorax 1982;37:564-71.  Back to cited text no. 15
    
16.
Hospital Authority Statistical Report 2014-2015. Available from: http://www.ha.org.hk/. [Last updated on 2016 May].  Back to cited text no. 16
    


    Figures

  [Figure 1], [Figure 2]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5]



 

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