The Duration of Wheezy Episodes in Early Childhood Is Independent of the Microbial Trigger
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1 The Duration of Wheezy Episodes in Early Childhood is Independent
2 of the Microbial Trigger
3 Christian J Carlsson, medical doctor1; Nadja H Vissing, PhD1; Astrid Sevelsted, MSc1; Sebastian
4 L Johnston, professor2; Klaus Bønnelykke, PhD1; Hans Bisgaard, professor1
5 1 The Copenhagen Prospective Studies on Asthma in Childhood; Faculty of Health and
6 Medical Sciences, University of Copenhagen and The Danish Pediatric Asthma Centre;
7 Copenhagen University Hospital, Gentofte, Ledreborg Allé 34, DK- 2820 Gentofte,
8 Copenhagen, Denmark
9 2Airway Disease Infection Section, National Heart and Lung Institute, MRC and Asthma UK
10 Centre in Allergic Mechanisms of Asthma, Imperial College London, UK
11 Correspondence to:
12 Professor Hans Bisgaard, MD, DMSci
13 Tel: (+45) 39777360 Fax: (+45) 39777129
14 E-mail: [email protected]
15 Website: www.copsac.com
16
17 Funding: COPSAC is funded by private and public research funds listed on www.copsac.com.
18 The Lundbeck Foundation, the Danish Strategic Research Council, the Pharmacy Foundation
19 of 1991, the Augustinus Foundation, the Danish Medical Research Council, and the Danish
20 Paediatric Asthma Centre provided the core support for COPSAC research centre. The
21 funding agencies had no role in the study design; the conduct of the study; data collection 22 and management; data analysis; or the preparation, review, or approval of the manuscript.
23 All authors are independent of any interests of the funders.
24 25 Abstract
26 Background: Wheezy episodes in young children are often triggered by viral and bacterial
27 respiratory infections, but there is little evidence supporting that symptom duration
28 depends on the specific microbial trigger.
29 Objective: To investigate if the duration of wheezy episodes in young children depends on
30 the microbial trigger.
31 Methods: 283 children from the Copenhagen Prospective Study on Asthma in Childhood2000
32 at-risk birth cohort were prospectively examined for common airway pathogenic bacteria
33 and viruses during acute wheezy episodes, in the first 3 years of life. Findings were related to
34 symptomatic duration of episodes as monitored in daily diary cards from birth.
35 Results: 837 samples were investigated for virus and/or bacteria. In 55% of episodes both
36 virus and bacteria were identified, in 31% bacteria exclusively and in 10% virus exclusively.
37 The median duration of acute symptoms was 9 days (interquartile range 5-16 days). The
38 duration was independent of bacteria or viral species.
39 Conclusions: The duration of wheezy episodes was independent of pathogenic airway
40 bacteria or virus species. This suggests that symptom burden from infections is dependent
41 on other factors, such as environmental exposures or host factors . The common term “viral
42 wheeze” seems inappropriate in view of the finding of pathogenic bacteria in 86% of wheezy
43 episodes.
44 Word count abstract: 2236 45 Key messages
46 - The duration of wheezy episodes in young children is independent of the specific viral
47 or bacterial triggers.
48 - The common term “viral wheeze” seems inappropriate in view of the finding of
49 pathogenic bacteria in the majority of wheezy episodes.
50 Capsule summary
51 Viral and bacterial respiratory infections are associated with acute wheezy episodes in young
52 children. The duration of wheezy episodes in young children is independent of the specific
53 infecting viral and bacterial species.
54 Key words: Respiratory Infections; Wheezy episodes; Pediatrics.
55 Word count: 3290 56 Abbreviations
57 95%CI = 95% confidence interval
58 COPSAC2000 = Copenhagen Prospective Study on Asthma in Childhood2000
59 GEE = Generalized estimating equations
60 IQR = Inter Quartile Range
61 IRR = Incidence Rate Ratio
62 RSV = Respiratory syncytial virus
63 RV = Rhinovirus
64
5 65 Background
66 Infections with respiratory viruses are known triggers of wheezy episodes in children with
67 reported infection rates of 62% - 95% 1–6 and 40% outside episodes. 5 Rhinoviruses (RV),
68 respiratory syncytial virus (RSV) and coronaviruses seem the most prevalent viruses during
69 wheezy episodes. 1–6 Several other respiratory viruses have been implicated with lesser
70 relative contributions. 1,3–6 In our recent study we highlighted that common pathogenic
71 bacteria and respiratory viruses were equally closely associated with wheezy episodes, 5
72 suggesting that bacteria should also be considered an important trigger.
73 The aim of this study was to address the question if the duration of wheezy episodes is
74 attributable specifically to the infecting species. If not, this would suggest host or
75 environmental factors to be responsible for the disease course as suggested by our recent
76 finding of an interaction between 17q21 gene risk variant, exposure to RV and risk of
77 persistent wheeze. 7 Therefore we have compared differences in the duration of wheezy
78 episodes, associated with various respiratory virus and bacteria species, in the Copenhagen
79 Prospective Study on Asthma in Childhood 2000 (COPSAC2000) at-risk birth cohort, followed
80 from birth with daily diary cards and acute visits to our clinic during wheezy episodes. 5,8,9
81
82 Methods
83 The Copenhagen Prospective Study on Asthma in Childhood 2000 (COPSAC2000) is a single-
84 centre, prospective birth cohort study following 411 children of mothers with doctor
6 85 diagnosed asthma. 8 Criteria for inclusion of subjects have been published previously 8,10 and
86 are summarized in the Online Repository.
87 Children in COPSAC2000 attended the research clinic during acute wheezy episodes, at which
88 time airway aspirates for microbiological diagnosis were collected. Wheezy symptoms were
89 recorded in daily diaries from 1 month of age until age 3 years. 8,9 Parents were taught to
90 record their child’s symptoms with emphasis on the lower airways, at comprehensive
91 educational sessions, conducted at planned half-yearly visits. Wheezy symptoms were
92 translated to the parents as any symptom significantly affecting the child’s breathing such as
93 noisy breathing (wheeze or whistling sounds), shortness of breath or persistent troublesome
94 cough affecting the sleep or activity of the child. Daily symptoms were recorded as
95 composite dichotomized scores (yes/no) each day; i.e. the parents were taught to make a
96 global assessment. The complexity of symptoms was detailed in a book that was given to the
97 parents (www.copsac.com/content/literature-parents). The diary cards were collected and
98 reviewed by the doctors at the planned half-yearly clinic visits.
99 Wheezy episodes were defined as three consecutive days on which the child had wheezing
100 symptoms. The parents were requested to bring the child to the clinical research unit for
101 examination by the research physician within 24 hours after every episode (i.e., on the
102 fourth consecutive day of symptoms). For some episodes, wheezy symptoms were not
103 recorded on the day of aspiration. These episodes were still included in the analysis if there
104 had been symptoms up until the day before aspiration. At each acute visit the children were
105 examined by physicians trained in paediatrics and clinical research for diagnosis and
106 treatment of wheezy episodes in accordance with predefined standard operating
7 107 procedures. Aspirates from acute respiratory episodes with clinical signs indicative of
108 pneumonia or croup were excluded from this study as described in the Online Repository.
109 Hypopharyngeal aspirates were obtained for routine bacterial cultures without any a priori
110 species selection (we detected Streptococcus pneumoniae, Haemophilus influenza,
111 Moraxella catarrhalis, Staphylococcus aureus and Streptococcus pyogenes) and
112 nasopharyngeal aspirates for PCR virus identification (picornaviruses; RSV; coronaviruses;
113 parainfluenza viruses; influenza viruses; human metapneumoviruses; adenoviruses and
114 bocavirus) at all acute visits as described in the Online Repository.
115 Various baseline host and environmental factors were invesitgated for potential confounding
116 effect on the association between microbial triggers and duration of wheezy episodes.
117 Allergic sensitization was determined from specific IgE and skin prick tests at the ages of 6
118 months, 1.5 years and 4 years. Asthma was diagnosed throughout the first three years of life
119 in accordance with international guidelines as further detailed in the Online Repository.
120 Allelic discrimination at the ORMDL3 locus rs7216389 at chromosome 17q21 was performed
121 using an Applied Biosystems Custom Taqman SNP Genotyping assay (c/n 4332072) on a 7700
122 Sequence Detection System. The variant was in Hardy-Weinberg equilibrium (P > 0.05). We
123 collected occipital hair samples at 1 year of age for determination of trace amounts of
124 nicotine using gas chromatography-mass spectrometry assays as previously described. 11
125
126 Statistical analyses
8 127 Microbial findings in wheezy episodes were summarized in frequency tables across all
128 episodes with available microbial data. Co-infection was defined as identification of at least
129 one respiratory virus and at least one of the investigated bacteria (S. pneumonia, H.
130 influenzae and M. catarrhalis).
131 The main outcome was duration of acute wheezy episodes where microbial sampling was
132 performed. The effect of various infectious agents on duration of episodes was investigated,
133 using generalized estimating equation (GEE), to adjust for inter-observational correlations,
134 due to multiple sampling from the same child. We assumed negative binomial distribution of
135 duration of episodes. Each infectious agent was investigated separately as a dichotomous
136 variable (present/not present) independent of other findings in sample. Results are shown
137 unadjusted and adjusted for confounders.
138 Distribution of potentially confounding environmental and host risk factors (sex; age at
139 episode; fathers asthma; mothers educational level; nicotine in hair age 1 year; sensitization
140 at ages 6 months, 18 months, 4 years; asthma during age 0-3 years; chromosome 17q21
141 variant) were summarized for the study base of wheezy episodes, and investigated for their
142 independent effect on duration of wheezy episodes, also using GEE.
143
144 The effect of infection with virus only, bacteria only or co-infection compared to no infection
145 was investigated in a sub-analysis. A significance level of 0.05 was used in all analyses. All
146 analyses were conducted in SAS statistical software (version 9.3).
9 147 To visualize the effect of various agents on symptom duration, not limiting the analyses to
148 consecutive days with symptoms, we plotted the percentage of diaries on which symptoms
149 were recorded on the day of sampling and for each day 30 days before and after sampling.
150 Results
151 The clinical follow-up rate of the COPSAC cohort was 95% at age 1 year; 90% at age 2 years
152 and 85% at age 3 years.
153 The study base (Figure 1) included 837 samples taken at wheezy episodes from 283 children
154 in the first three years of life. Cultures were excluded if antibiotics had been taken within the
155 previous week of sampling (N=74). Samples taken in relation to a clinical diagnosis of
156 pneumonia (N=163) were excluded and samples taken in relation to a clinical diagnosis of
157 croup (N=8) were also excluded leaving 592 eligible samples from 240 children. Of these, 540
158 samples were investigated for virus; 483 were investigated for bacterial findings and 431
159 were investigated for both.
160 During the first 3 years of life 96 children contributed 1 aspirate, 112 contributed 2-4
161 aspirates and 32 children contributed 5 or more aspirates with either virus or bacteria. 171
162 of 411 children (42%) had no eligible aspirates performed during wheezy episodes. Details
163 on numbers of eligible bacterial and viral aspirates per child are displayed in Figure E1 in the
164 Online Repository.
165 While we encouraged the parents to bring their child to the research clinic after three
166 consecutive days of wheezy symptoms this was not always the case. If parents and children
10 167 attended the clinic after only 1-2 days of troublesome lung symptoms (N=23), aspirates were
168 still obtained according to standard operating procedures described above.
169 Table 1 shows the distribution of viruses and bacteria in the samples taken during wheezy
170 episodes. Picornaviruses (of which 84% was RV), RSV and coronaviruses were the most
171 prevalent viral agents present in 29%, 17% and 13% of samples with lesser relative
172 contributions of other viruses. S. pneumonia, M. catarrhalis and H. influenzae were found in
173 47%, 49% and 41% of the samples while S. aureus and S. pyogenes were found in an
174 insignificant proportion of samples and were excluded from further analyses In 55% of
175 wheezy episodes co-infection with both virus and bacteria was identified. Exclusively
176 bacterial or viral infection was found in 31% and 10% of episodes respectively. In 5% of
177 samples no pathogen was identified. There were no increased risk of co-infection with any
178 type of pathogen i.e., infection with virus did not cause greater risk of bacterial infection and
179 vice versa (Chi square p=0.59).
180 There were no apparent difference in age at first infection between investigated viruses and
181 bacteria, and there were no obvious age-dependent differences in prevalence of any of the
182 pathogens (details in Figure E2 and E3).
183 Figure 2 shows the seasonal variation of viruses and bacteria found during acute respiratory
184 episodes. RSV exhibited a marked peak during winter months while the all other viruses and
185 bacteria were found in stable proportions throughout the year. For both viruses and bacteria
186 a larger percentage of aspirates were without pathogen findings during summer months.
187 During the first three years of follow-up, symptom diary data was completed for 387
188 children in a total of 374,264 days of the potential 450,867 days of observation i.e. a
11 189 coverage rate of 83%. The median age for starting the diary recordings was 19 days
190 (Interquartile range 13-29). Wheezy symptoms were recorded on 6.6% (24,708) of the days.
191 Twenty-four children had no dairy data for the first three years of life. Forty-five children
192 never recorded any symptom days throughout the first three years of follow-up.
193 515 (91%) of the 592 eligible aspirates were taken from episodes with complete diary data
194 one month before and one month after the sample collection. Thus we analysed a total of
195 515 samples in 216 children (Figure 1).
196 The median duration of the 515 wheezy episodes was 9 days (IQR 5 to 16). The effect of
197 various environmental and host factors on duration of episodes are shown in Table 2. A
198 diagnosis of asthma during age 0-3 years was associated with significantly longer duration of
199 wheezy episodes (IRR 1.74, [1.32-2.30], p=<0.001) while there was no evidence of
200 association with the other risk factors.
201 There was no significant difference in duration of wheezy episodes associated with any
202 specific viral or bacterial trigger (Table 3). Similarly, symptom duration was independent of
203 the presence of solely viral or bacterial infection or co-infection compared to episodes with
204 no pathogens detected (Table E1). Adjusting the analyses for potential confounding effect of
205 various environmental and host factors did not change the results (Table 3 and E1).
206 Figure 2A shows the proportion of diaries on which symptoms were recorded for each day
207 during the 30-day period before and after an aspirate with positive findings for respiratory
208 viruses. In the immediate period surrounding positive viral aspirates, there were no
209 discernible differences in the portion of children with wheezy symptoms between different
210 virus species; i.e. all virus triggered wheezy episodes of similar symptom profile. The level of
12 211 baseline respiratory symptoms before and after the wheezy episodes was also similar among
212 the investigated viruses, i.e. no species caused more sustained symptoms than others. It was
213 evident that the majority of families attended the research clinic for clinical examination and
214 airway aspiration (day 0) after a period of a few symptom days in accordance with our
215 protocol. Again this was true for all the most common respiratory viruses.
216 Figure 2B shows the proportion of diaries on which symptoms were recorded for each day
217 during the 30 day period before and after an aspirate with positive findings for the
218 pathogenic respiratory bacteria. There were no differences in the course of disease and
219 remission between bacterial species. The level of baseline respiratory symptoms before and
220 after the wheezy episode was similar among the investigated bacteria.
221 Figure 2C shows the proportion of diaries on which symptoms were recorded for each day
222 during the 30 day period before and after an aspirate with positive findings for only virus,
223 only bacteria, co-infection or no identified pathogens. Symptom duration was similar for the
224 three groups with positive microbiological findings. Symptomatic episodes with no identified
225 pathogens were rare and thus appeared to have a more erratic course with fewer baseline
226 symptoms before the wheezy episode.
227
228 Discussion
229 Pathogenic bacteria were a more common finding than virus during wheezy episodes, hence
230 the common term “viral wheeze” should be abandoned. Duration of wheezy episodes was
231 independent of specific pathogenic respiratory bacteria or virus species. This suggests that
13 232 symptom burden from infections in terms of duration of wheezy episodes is dependent on
233 other factors than the specific triggering agent. .
234 Strengths and weaknesses of the study
235 The intense clinical surveillance of the COPSAC2000 birth cohort is a major strength of this
236 study. All children attended the COPSAC research clinic instead of other healthcare facilities.
237 Experienced research physicians did clinical diagnosis and sampling at the clinic in
238 accordance with standard procedures. This approach reduced the risk of misclassification of
239 illness and variation in sampling quality. The physicians at the clinic distinguished clinical
240 pneumonia from wheezy episodes on the basis of the presence of tachypnoea, fever, and
241 crepitation on auscultation without wheeze in accordance with standard operating
242 procedures. This clinical differentiation between wheeze and pneumonia can be debated.
243 However, the children were assessed by the same doctors in accordance with standard
244 operating procedures; the sampling for viruses and bacteria was independent of such a
245 distinction, and the clinical diagnosis was independent of microbiological results.
246 Another strength of this study is the prospective monitoring of lung symptoms in daily
247 diaries since neonatal age. This assured reliable monitoring of episode duration. The validity
248 of mother’s symptom observation and recording was probably improved from the fact that
249 they all had a history of asthma.
250 The incidence of viruses in wheezy episodes in this study is comparable to other recent
251 studies of viral infections in wheezy episodes of infants and preschool children. 2–4,6
14 252 It is a limitation of this study that we do not have data on symptom severity. It is our
253 interpretation that symptom duration is a surrogate marker of symptom severity, but this
254 needs to be studied.
255 According to the study protocol we instructed the parents to bring their child to the research
256 clinic after three consecutive days of symptoms. This potentially hampers our ability to
257 analyse duration of episodes. As some parents brought their child to the research clinic after
258 only 1-2 days of symptoms we do have some samples (N=23) from episodes of shorter
259 duration and these are included in the analysis. Comparison of the microbial spectrum for
260 the lower and upper quartile of duration of wheezy episodes included (1-5 days vs. 17-28+
261 days) did not reveal any differences (data not shown).
262 The use of traditional culturing methods is a limitation. Unfortunately, bacterial DNA
263 sequencing data were not available in the current study.
264 Another limitation of our findings is that the investigations were carried out in a high-risk
265 population. The selection for maternal asthma and exclusion of premature newborns limit
266 the generalizability of the findings, which need replication in unselected cohorts.
267
268 Meaning of this study
269 Viral and bacterial infections are triggers of wheezy episodes in young children. 1,5 This study
270 shows similar symptom duration of acute wheezy episodes from the most common
271 respiratory bacteria and viruses. These findings suggest that the particular pathogenic
272 species is not important for the course of such episodes. This conclusion is supported by our
15 273 recent findings of similar relative distributions of specific bacterial and viral species in
274 symptomatic and asymptomatic children. 5 The notion that different species cause different
275 clinical outcomes might be confounded by prevalence and there is little evidence to signify
276 that the role of the infectious agent among pathogenic respiratory bacteria and virus is
277 dependent on species.
278 Previous reports have been conflicting as to whether the presence of viral infection
279 augments severity and duration of lower respiratory tract symptoms, and differential
280 symptom burden for specific viruses has been reported in some studies. 1,12,13 School children
281 were reported to have a lesser fall in peak expiratory flow and a lower subjective symptom
282 score when infected with coronaviruses than with other respiratory viruses. 1 Others
283 reported picornaviruses and adenoviruses to be more prevalent in near-fatal adult asthma
284 than in less severe exacerbations. 12 One important difference from our study is that these
285 phenotypes are much different from the wheezy episodes in young children.
286 Wheezy episodes are a much debated diagnosis to the point that the debate often confuse
287 the need to understand, prevent and treat this entity. Wheeze is the most common reason
288 for acute hospitalization, healthcare utilization and use of medicine in the young children in
289 westernized countries. 14 The terminology is misleading since evidence shows wheeze is an
290 unusual symptom for parents to report even prior to severe exacerbations, 15 and that the
291 quantitative global assessment of significant troublesome lung symptoms in the first 3 years
292 of life is a better predictor of asthma than assessment of wheeze alone 16. The common term
293 viral wheeze is further obsolete given the fact that bacteria seem more prevalent in such
294 episodes than virus.
16 295 In the COPSAC birth cohort studies we have instead educated the parents to record the
296 global respiratory distress being it wheeze, breathlessness, cough or what others terms lay-
297 people relate to this. Symptoms severely affecting the well-being of the child is the key to
298 the recordings in the diary cards. Though we find “wheezy episodes” a misnomer, we need
299 to use the term to be able to communicate our research.
300 Our results suggest that while microbiological pathogens act as instigators of respiratory
301 distress in children, other factors determines duration of the symptomatic episode. The
302 mechanisms by which viruses and bacteria provoke exacerbations are yet unclear but
303 current evidence suggests that allergic sensitization and altered immune response may be
304 more important than the virulence of the specific agent. 24 It has been suggested that
305 deficiencies in antiviral activity and the integrity of the airway epithelial barrier may make
306 individuals with asthma more likely to have severe viral respiratory infections of the lower
307 airway. 24 In this study we found asthma at age three years to be associated with episodes of
308 longer duration. This finding was not unexpected since persistent symptoms is one of the
309 diagnostic criteria for asthma. None of the other host factors investigated had any
310 confounding effect on duration of episodes.
311 RSV showed a peak in winter, with no other species-specific variation with respect to season
312 or age. There was however a general decrease in the proportion of infections per wheezy
313 episode during summer. The latter is an unexpected and interesting observation, but the
314 interpretation uncertain.It is a common notion that virus is the predominant microbial agent
315 responsible for acute respiratory symptoms in young children. However, we recently found
316 bacterial infections to be significantly associated with acute wheezy episodes in children up
17 317 to three years of age, similar to but independent of the well known association with viral
318 infections. 5 In this study we showed a high prevalence of concurrent infection with both
319 virus and bacteria (55%) and of exclusively bacterial infection (31%) in acute symptomatic
320 episodes. Surprisingly only few aspirates were found with only virus species (10%). This is of
321 apparent clinical interest as acute episodes with bacteria may be amendable to antibiotic
322 therapy or prophylaxis.
323 Conclusion
324 We found no significant differences in duration of wheezy episodes from the most common
325 pathogenic respiratory virus and bacteria. While triggered by virus and bacteria, the course
326 of wheezy episodes seems independent of infecting species and may therefore be controlled
327 by other factors such as intrinsic host factors or environmental exposures.
328 Acknowledgements
329 We gratefully express our gratitude to the children and families of the COPSAC2000 cohort
330 study for all their support and commitment. We acknowledge and appreciate the unique
331 efforts of the Copenhagen Prospective Study on Asthma in Childhood (COPSAC) research
332 team, and T. Kebadze and J. Aniscenko for the virologic analyses. COPSAC is funded by
333 private and public research funds listed on www.copsac.com. The Lundbeck Foundation, the
334 Danish Strategic Research Council, the Pharmacy Foundation of 1991, the Augustinus
335 Foundation, the Danish Medical Research Council, and the Danish Paediatric Asthma Centre
336 provided the core support for COPSAC research centre.
337
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413
21 414 Table 1: Viral and bacterial findings in pharyngeal aspirates obtained during wheezy episodes
415 in young children.
Numbers Percentage Viruses Picornaviruses 159/540 29% Respiratory syncytial virus 89/540 17% Coronaviruses 69/540 13% Other virus (5 below) 129/540 24% Parainfluenza viruses 42/540 8% Influenza viruses 36/540 7% Human metapneumoviruses 17/540 3% Adenoviruses 5/540 1% Bocavirus 43/540 8% Any virus (of above) 350/540 65% Multiple virus (of above) 183/540 34% Bacteria S. pneumoniae 229/483 47% H. influenzae 200/483 41% M. catarrhalis 238/483 49% Any bact (of above) 412/483 85% Multiple bacteria (of above) 205/483 42% Tested for Only virus 42/431 10% both Only bacteria 132/431 31% Both 237/431 55% No pathogens 20/431 5% 416
417
418
419
420
22 421 Table 2. Effect of environmental and host factors on duration of wheezy episodes in young
422 children.
N N children IRR [CI 95]; p-value episodes
Gender 515 216 Female 288 115 0.97 [0.72- 1.30]; 0.85 Male 227 101 reference Age 515 216 0--1 years 227 136 1.22 [0.82- 1.81]; 0.33 1--2 years 205 139 1.13 [0.75- 1.70]; 0.56 2--3 years 83 62 reference Farther with a diagnosis of asthma 485 205 Yes 100 33 0.93 [0.70- 1.25]; 0.65 No 385 172 reference Maternal educational level 505 210 At most college 333 137 1.01 [0.73- 1.41]; 0.94 Medium duration 127 50 0.99 [0.60- 1.62]; 0.963 University 45 23 reference Environmental tobacco exposure (nicotine 491 207 in hair age 1 year above 1 ng/mg vs. below) Yes 206 90 1.16 [0.86- 1.56]; 0.34 No 285 117 reference Sensitization at any point (6 months, 18 512 214 months, 4 years) Yes 183 52 0.82 [0.64- 1.04]; 0.10 No 329 162 reference Asthma during age 0-3 years (yes vs. no) 478 198 Yes 183 52 1.74 [1.32- 2.30]; <0.001 No 295 146 reference Chromsome 17q21 gene variant 509 211 TT 170 72 1.05 [0.67- 1.66]; 0.83 TC 227 88 0.87 [0.56- 1.35]; 0.54 CC 112 51 reference IRR: Incidence rate ratio.
23 423 Table 3: Duration of wheezy episodes in young children, in relation to various viral and bacterial triggers.
Negative Positive Results from GEE models Median days No. of No. of Median days No. of No. of Unadjusted IRR [95% CI]; p- Confounder* (IQR) episodes children (IQR) episodes children value N=483 episodes adjusted IRR (N) (n) (N) (n) [95% CI]; p- value N=403 episodes Virus Picornaviruses 10 (6-16) 345 184 9 (6-17) 138 101 0.91 [0.74- 1.13]; 0.40 0.88 [0.71- 1.08]; 0.22 RSV 9 (6-17) 402 192 11 (7-15) 81 73 0.94 [0.76- 1.16]; 0.54 0.99 [0.78- 1.26]; 0.95 Coronaviruses 10 (6-17) 422 202 9 (5-13) 61 47 1.04 [0.68- 1.58]; 0.85 1.00 [0.70- 1.42]; 0.99 Other virus 10 (6-16) 366 182 10 (6-17) 117 88 1.05 [0.86- 1.29]; 0.61 1.06 [0.87- 1.3]; 0.55 Any virus 9 (6- 17) 171 117 10 (6- 17) 312 171 0.97 [0.78- 1.22]; 0.81 0.95 [0.74- 1.21]; 0.67 Bacteria S. pneumoniae 9 (6-16) 224 134 11 (6-19) 196 130 1.22 [0.99- 1.49]; 0.058 1.18 [0.94- 1.48]; 0.16 H. influenzae 10 (6-18) 243 154 11 (6-17) 177 113 0.98 [0.79- 1.22]; 0.88 1.00 [0.78- 1.27]; 0.99 M. catarrhalis 11 (6-18) 215 128 10 (6-17) 205 135 1.02 [0.82- 1.27]; 0.85 1.03 [0.84- 1.27]; 0.76 Any bacteria 9 (5- 16) 62 47 11 (6- 17) 358 180 1.22 [0.99- 1.51]; 0.059 1.17 [0.94- 1.45]; 0.15 424 * Sex; age at episode; fathers asthma; mothers educational level; nicotine in hair age 1 year; sensitization at ages 6 months, 18 months, 4
425 years; asthma during age 0-3 years; chromosome 17q21 variant. IRR: Incidence rate ratio; GEE: generalized estimating equations
24 426 Figure legends
427 Figure 1: Study base selection of samples from young children with wheezy episodes,
428 analyzed for viruses and bacteria.
429 Figure 2: Seasonal variation in prevalence of viruses and bacteria found during wheezy
430 episodes in young children. The y-axis gives the proportion of aspirates with relevant
431 findings within each month while the x-axis represents calendar months. RSV: respiratory
432 syncytial virus.
433 Figure 3A: Days with wheezy symptoms before and after pharyngeal sampling (day 0) with
434 positive findings of various respiratory viruses. RSV: respiratory syncytial virus.
435 Figure 3B: Days with wheezy symptoms before and after pharyngeal sampling (day 0) with
436 positive findings of various respiratory bacteria.
437 Figure 3C: Days wheezy symptoms before and after pharyngeal sampling (day 0) with no
438 microbial findings, only viral findings, only bacterial findings or both virus and bacteria
439 detected.
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