Risk factors for wheezing in a subtropical environment: role of respiratory viruses and allergen sensitization.
ABSTRACT Risk factors for acute wheezing among children in subtropical areas are largely unknown.
To investigate the role of viral infections, allergen sensitization, and exposure to indoor allergens as risk factors for acute wheezing in children 0 to 12 years old.
One hundred thirty-two children 0 to 12 years of age who sought emergency department care for wheezing and 65 children with no history of wheezing were enrolled in this case-control study. Detection of respiratory syncytial virus antigen, rhinovirus and coronavirus RNA, adenovirus, influenza, and parainfluenza antigens was performed in nasal washes. Total IgE and specific IgE to mites, cockroach, cat, and dog were measured with the CAP system. Major allergens from mites, cockroach, cat, and dog were quantified in dust samples by ELISA. Univariate and multivariate analyses were performed by logistic regression.
In children under 2 years of age, infection with respiratory viruses and family history of allergy were independently associated with wheezing (odds ratio, 15.5 and 4.2; P = .0001 and P = .008, respectively). Among children 2 to 12 years old, sensitization to inhalant allergens was the major risk factor for wheezing (odds ratio, 2.7; P = .03). High-level allergen exposure, exposure to tobacco smoke, and lack of breast-feeding showed no association with wheezing.
Some risk factors for wheezing previously identified in temperate climates were present in a subtropical area, including respiratory syncytial virus infection in infants and allergy in children older than 2 years. Rhinovirus was not associated with wheezing and did not appear to be a trigger for asthma exacerbations.
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ABSTRACT: The relevance of allergic sensitization, as judged by titers of serum IgE antibodies, to the risk of an asthma exacerbation caused by rhinovirus is unclear. We sought to examine the prevalence of rhinovirus infections in relation to the atopic status of children treated for wheezing in Costa Rica, a country with an increased asthma burden. The children enrolled (n= 287) were 7 through 12 years old. They included 96 with acute wheezing, 65 with stable asthma, and 126 nonasthmatic control subjects. PCR methods, including gene sequencing to identify rhinovirus strains, were used to identify viral pathogens in nasal washes. Results were examined in relation to wheezing, IgE, allergen-specific IgE antibody, and fraction of exhaled nitric oxide levels. Sixty-four percent of wheezing children compared with 13% of children with stable asthma and 13% of nonasthmatic control subjects had positive test results for rhinovirus (P< .001 for both comparisons). Among wheezing subjects, 75% of the rhinoviruses detected were group C strains. High titers of IgE antibodies to dust mite allergen (especially Dermatophagoides species) were common and correlated significantly with total IgE and fraction of exhaled nitric oxide levels. The greatest risk for wheezing was observed among children with titers of IgE antibodies to dust mite of 17.5 IU/mL or greater who tested positive for rhinovirus (odds ratio for wheezing, 31.5; 95% CI, 8.3-108; P< .001). High titers of IgE antibody to dust mite allergen were common and significantly increased the risk for acute wheezing provoked by rhinovirus among asthmatic children.The Journal of allergy and clinical immunology 05/2012; 129(6):1499-1505.e5. · 12.05 Impact Factor
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ABSTRACT: Many bacterial components in indoor dust can evoke inflammatory pulmonary diseases. Bacteria secrete nanometre-sized vesicles into the extracellular milieu, but it remains to be determined whether bacteria-derived extracellular vesicles in indoor dust are pathophysiologically related to inflammatory pulmonary diseases. To evaluate whether extracellular vesicles (EV) in indoor air are related to the pathogenesis of pulmonary inflammation and/or asthma. Indoor dust was collected from a bed mattress in an apartment. EV were prepared by sequential ultrafiltration and ultracentrifugation. Innate and adaptive immune responses were evaluated after airway exposure of EV. Repeated intranasal application of indoor-dust-induced neutrophilic pulmonary inflammation accompanied by lung infiltration of both Th1 and Th17 cells. EV 50-200 nm in diameter were present (102.5 μg protein concentration/g dust) in indoor dust. These vesicles were internalized by airway epithelial cells and alveolar macrophages, and this process was blocked by treatment of polymyxin B (an antagonist of lipopolysaccharide, an outer-membrane component of Gram-negative bacteria). Intranasal application of 0.1 or 1 μg of these vesicles for 4 weeks elicited neutrophilic pulmonary inflammation. This phenotype was accompanied by lung infiltration of both Th1 and Th17 cells, which were reversed by treatment of polymyxin B. Serum dust EV-reactive IgG1 levels were significantly higher in atopic children with asthma than in atopic healthy children and those with rhinitis or dermatitis. CONCLUSION & CLINICAL RELEVANCE: Indoor dust EV, especially derived from Gram-negative bacteria, is a possible causative agent of neutrophilic airway diseases.Clinical & Experimental Allergy 04/2013; 43(4):443-54. · 4.79 Impact Factor
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ABSTRACT: Epidemiological evidence suggests that helminth infection and rural living are inversely associated with allergic disorders. To investigate the effect of helminth infections and urban versus rural residence on allergy in schoolchildren from Ghana. In a cross-sectional study of 1,385 children from urban-high socioeconomic status (SES), urban-low SES and rural schools, associations between body mass index (BMI), allergen-specific IgE (sIgE), parasitic infections and allergy outcomes were analysed. Allergy outcomes were skin prick test (SPT) reactivity, reported current wheeze and asthma. Helminth infections were found predominantly among rural subjects and the most common were hookworm (9.9%) and Schistosoma spp (9.5%) Overweight was highest among urban-high SES (14.6%) compared to urban-low SES (5.5%) and rural children (8.6%). The prevalence of SPT reactivity to any allergen was 18.3% and this was highest among rural children (21.4%) followed by urban-high SES (20.2%) and urban-low SES (10.5%) children. Overall, SPT reactivity to mite (12%) was most common. Wheeze and asthma were reported by 7.9% and 8.3% respectively. In multivariate analyses, factors associated with mite SPT were BMI (aOR 2.43, 95% CI 1.28 - 4.60, p=0.007), schistosome infection (aOR 0.15, 95% CI 0.05-0.41), and mite sIgE (aOR 7.40, 95% CI 5.62 - 9.73, p< 0.001) but not area. However, the association between mite IgE and SPT differed by area and was strongest among urban-high SES children (aOR = 15.58, 95% CI 7.05-34.43, p<0.001). Compared to rural, urban-low SES area was negatively associated with current wheeze (aOR 0.41, 95% CI 0.20-0.83, p=0.013). Both mite sIgE and mite SPT were significantly associated with current wheeze and asthma. Infection with Schistosoma appeared to protect against mite SPT reactivity. This needs to be confirmed in future studies, preferably in a longitudinal design where schistosome infections are treated and allergic reactions re-assessed. This article is protected by copyright. All rights reserved.Clinical & Experimental Allergy 03/2014; · 4.79 Impact Factor
Health care delivery
Health care delivery and quality
Risk factors for wheezing in a
subtropical environment: Role of
respiratory viruses and allergen
Ataide A. Camara, MD,a,bJorgete M. Silva, MD,aVirginia P . L. Ferriani, MD,a
Kátia R. C.Tobias, MSc,aIzolete S. Macedo, MSc,cMárcio A. Padovani, MD,c
Charlotte M. Harsi, PhD,dM. Regina A. Cardoso, PhD,eMartin D. Chapman, PhD,f
Eurico Arruda, MD,cThomas A. E. Platts-Mills, MD, PhD,gand L. Karla Arruda, MDa
Ribeirão Preto and São Paulo, Brazil, and Charlottesville, Va
Background: Risk factors for acute wheezing among children
in subtropical areas are largely unknown.
Objective: To investigate the role of viral infections, allergen
sensitization, and exposure to indoor allergens as risk factors
for acute wheezing in children 0 to 12 years old.
Methods: One hundred thirty-two children 0 to 12 years of age
who sought emergency department care for wheezing and 65
children with no history of wheezing were enrolled in this
case-control study. Detection of respiratory syncytial virus
antigen, rhinovirus and coronavirus RNA, adenovirus, influen-
za, and parainfluenza antigens was performed in nasal washes.
Total IgE and specific IgE to mites, cockroach, cat, and dog
were measured with the CAP system. Major allergens from
mites, cockroach, cat, and dog were quantified in dust samples
by ELISA. Univariate and multivariate analyses were per-
formed by logistic regression.
Results: In children under 2 years of age, infection with respi-
ratory viruses and family history of allergy were independent-
ly associated with wheezing (odds ratio, 15.5 and 4.2; P = .0001
and P = .008, respectively). Among children 2 to 12 years old,
sensitization to inhalant allergens was the major risk factor for
wheezing (odds ratio, 2.7; P = .03). High-level allergen expo-
sure, exposure to tobacco smoke, and lack of breast-feeding
showed no association with wheezing.
Conclusions: Some risk factors for wheezing previously identi-
fied in temperate climates were present in a subtropical area,
including respiratory syncytial virus infection in infants and
allergy in children older than 2 years. Rhinovirus was not
associated with wheezing and did not appear to be a trigger
for asthma exacerbations. (J Allergy Clin Immunol
Key words: Wheezing, asthma, allergy, mites, cockroach, respira-
tory viruses, respiratory syncytial virus, rhinovirus, allergens
Asthma is the most common chronic disease of child-
hood. Evidence indicates that more than half of the cases
of persistent asthma start before the age of 3 years, and it
is now clear that airway inflammation and irreversible
remodeling may be initiated early in life.1,2 Definitive
diagnosis of asthma and subsequent decision to initiate
long-term anti-inflammatory treatment at an early age
has been a challenge in pediatric practice.3 Although
asthma in young children appears to represent a hetero-
geneous disease with distinct phenotypes, sensitization
to common inhalant allergens including those derived
from dust mites, cockroach, cat, and Alternaria remains
a major risk factor for persistent asthma associated with
airway hyperreactivity and decreased lung function.4-6
Respiratory viruses have been recognized as major
triggers of wheezing episodes and asthma exacerbation.7
In the northern hemisphere, respiratory syncytial virus
(RSV) accounts for the majority of wheezing episodes in
children younger than 2 years of age, being detected in
60% to 80% of infants.7 Results of the Tucson Children’s
Respiratory Study8 revealed that lower respiratory tract
infection with RSV early in life was associated with per-
sistent wheezing; however, by age 13 years, lung func-
tion abnormalities were no longer present and wheezing
resolved in most children. In one study, severe RSV
bronchiolitis in the first year of life has been linked to
asthma and allergic sensitization at age 7 years9; howev-
er, studies to determine whether RSV infections enhance
allergy have provided conflicting results.7 It has been
definitely established that specific IgE response to RSV
is not an important element in the pathogenesis of RSV-
induced wheezing10; however, the virus has been shown
From the aDepartment of Pediatrics, School of Medicine of Ribeirão Preto,
University of São Paulo, Brazil; bSanta Lydia Hospital, Ribeirão Preto,
Brazil; the cDepartment of Cell and Molecular Biology, School of Medi-
cine of Ribeirão Preto, University of São Paulo, Brazil; the dInstitute of
Biomedical Sciences, University of São Paulo, Brazil; the eDepartment of
Epidemiology, School of Public Health, University of São Paulo, Brazil;
fIndoor Biotechnologies, Inc, Charlottesville, Va; and the gAsthma and
Allergic Diseases Center, University of Virginia, Charlottesville.
Received for publication August 13, 2003; revised November 2, 2003; accept-
ed for publication November 11, 2003.
Reprint requests: L. Karla Arruda, MD, Department of Pediatrics, School of
Medicine of Ribeirão Preto, University of São Paulo, Av Bandeirantes
3900, Ribeirão Preto, SP, 14049-900, Brazil.
Supported by FAPESP grants 95/9690-0 and 00/01875-0, CNPq-Instituto de
Investigação em Imunologia (iii), and National Institutes of Health grant
AI-20565. V.P.L.F., E.A., and L.K.A are recipients of CNPq scholarships.
M.D.C. was supported in part by a research grant from Philip Morris Inc
to Indoor Biotechnologies, Inc.
© 2004 American Academy of Allergy, Asthma and Immunology
552 Camara et al
J ALLERGY CLIN IMMUNOL
to induce expression of cytokines and chemokines and
activation of monocytes, macrophages, and lymphocytes,
which may influence the mechanisms involved in the
development of asthma in children.7 In older children,
rhinovirus becomes the dominant viral pathogen linked
to wheezing exacerbations. This has been demonstrated
in community-based and emergency department stud-
ies.11,12 In the emergency department setting, rhinovirus
infections act synergistically with allergen sensitization
and/or allergen exposure to induce severe asthma symp-
toms in both children and adults.12,13 In keeping with
this, lower respiratory tract symptoms and markers of
inflammation in young adults with mild asthma experi-
mentally infected with rhinovirus are more pronounced
in those with high total IgE.14 It is thought that a defi-
cient TH1-type response with decreased IFN-γ produc-
tion underlies the observation that rhinovirus infections
in atopic individuals are more severe and longer-lasting
and induce more lower respiratory symptoms as com-
pared with nonatopic subjects.15
The purpose of the current study was to investigate the
role of viral infections, allergen sensitization, and expo-
sure to indoor allergens as risk factors for acute wheez-
ing in children 0 to 12 years old living in a subtropical
environment. The results of the current study may con-
tribute to promote better care of children with wheezing
in these areas.
One hundred thirty-two children 0 to 12 years of age (80 boys)
who sought emergency department (ED) care for wheezing either at
the Clinical Hospital of the University of São Paulo School of Med-
icine of Ribeirão Preto or Santa Lydia community Hospital were
enrolled in this case-control study. Patients were selected for the
study if they presented with wheezing that required therapy with
inhaled β2-agonists as judged by the attending physician. In addi-
tion, 65 children 0 to 12 years of age (39 boys) without respiratory
symptoms and no previous history of wheezing who sought ED care
at the same hospitals for other reasons were selected as control sub-
jects. The most frequent complaints among the control subjects were
acute gastroenteritis, fever, abdominal pain, headache, vomiting, and
seizures. Children with chronic respiratory illnesses (n = 2) (bron-
chopulmonary dysplasia) and those who reported therapy with corti-
costeroids within 4 weeks before the ED visit (n = 8) were not
included in the study. All children were residents in the city of
Ribeirão Preto. Wheezing and control children were enrolled every
month from October 1998 to June 2000, except for December 1998.
Approximately 3% of all children seen in the ED over the study peri-
od were enrolled in the study, and 95% of the children approached
were enrolled. Peaks of attendance to the ED for wheezing were
observed in both years; 61% and 68%, respectively, of wheezing and
control children under 2 years of age were enrolled from February
through May and 52% and 60% of wheezing and control children
older than 2 years were enrolled from March through June.
Parents or guardians completed a questionnaire that included
questions on personal and family history of allergies and asthma,
passive exposure to tobacco smoke, breast-feeding, and housing
conditions. A positive personal history of allergy was defined as a
report of physician-diagnosed asthma, rhinitis, and/or atopic der-
matitis. A positive family history for allergy was characterized by
the report of asthma, rhinitis, and/or atopic dermatitis diagnosed by
a physician in the mother, father, and/or sibling(s). History of prior
wheezing illnesses was reported for 48% of the wheezing children
younger than 2 years and for 93% of the older wheezing children.
However, only 16% of the wheezing infants and 51% of the wheez-
ing children older than 2 years reported asthma diagnosed by a
physician. The study protocol was approved by the ethics commit-
tee of both hospitals and the children’s parents and/or guardians
gave written informed consent to participate in the study.
Detection of respiratory viruses
Nasal washings were collected and processed for detection of res-
piratory viruses as previously described.12 RSV antigen was detect-
ed by using both a rapid enzyme immunoassay (Test-Pack, Abbott,
Chicago, Ill) and an indirect immunofluorescence (Chemicon,
Temecula, Calif). Human rhinovirus and coronavirus RNA was
detected by RT-PCR.12,16 Influenza and parainfluenza viruses were
detected by indirect immunofluorescence.17,18 In a subset consisting
of 90 of 132 wheezing children and 48 of 65 control subjects, from
whom remaining material was available, detection of adenovirus was
investigated by culture of frozen nasal aspirates on A549 cells, with
cytopathic effect confirmed by immunofluorescence. Typing of ade-
novirus isolated from cultures to the subgenus level was performed
by amplification of the VA-RNA region of the viral genome by PCR,
according to previously described method.19 PCR products of 520 to
522 bp and 505 bp in length corresponded to adenovirus subgenera
B and C, respectively. Certain adenovirus serotypes including those
of subgenus C can be identified in nasal aspirates up to several weeks
after acute infection.20 To minimize the interference of latent aden-
ovirus, only subgenus B was included in the analysis.
Total IgE, specific IgE antibodies, and
peripheral blood eosinophils
Serum levels of total IgE and specific IgE to mites (Der-
matophagoides pteronyssinus, D farinae, and Blomia tropicalis),
cockroach (Blattella germanica), cat, dog, foods (cow’s milk, egg,
wheat, soy, peanut, and fish), and to Ascaris lumbricoides were
measured with the use of the UniCAP system (Pharmacia, Uppsala,
Sweden). Specific IgE levels ≥0.7 kU/L (CAP score ≥2) were con-
sidered positive. Automated white blood cell counts were carried
out with the use of a Colter T540 system, and differential counts,
including eosinophil quantification, were performed manually.
Allergen levels in house dust samples
Dust samples were collected from four sites in each subject’s
home: bedding, bedroom floor, TV room, and kitchen, within 3
weeks of the ED visit. Dust collection and preparation of dust extracts
were performed according to standard procedures.21 Measurements
of major allergens from mites (group 1 and group 2), cockroach (Bla
g 1 and Bla g 2), cat (Fel d 1), and dog (Can f 1) in dust extracts were
carried out with the use of monoclonal antibody–based ELISA.22
Group 1 mite allergens comprised the sum of levels of Der p 1 and
Der f 1. Group 2 allergens (Der p 2 and Der f 2) were simultaneous-
ly detected in the monoclonal antibody ELISA with a cross-reactive
capture antibody (1D8). High-level exposure was defined as the pres-
ence of at least one dust sample in the house containing concentra-
tions of group 1 mite allergens (≥10 µg/g, Bla g 1 ≥8 U/g, and/or Bla
g 2 ≥0.32 µg/g, Fel d 1 ≥8 µg/g, and Can f 1 ≥10 µg/g).22
Health care delivery
ED: Emergency department
GM: Geometric mean
RSV: Respiratory syncytial virus
Health care delivery
J ALLERGY CLIN IMMUNOL
VOLUME 113, NUMBER 3
Camara et al 553
Data from wheezing and control children were compared in two
age groups: children younger than 2 years of age (n = 74 and n = 30,
respectively) and children 2 to 12 years of age (n = 58 and n = 35,
respectively). Data on total IgE levels were log-transformed and
analyzed by Student t test. Peripheral blood eosinophils and aller-
gen levels in house dust were analyzed by Mann-Whitney test. Chi-
square analysis was used to compare the prevalence of elevated spe-
cific IgE, positive viral tests, frequency of passive smoke exposure,
and high-level allergen exposure. Univariate and multivariate analy-
sis were carried out by logistic regression, using the software
STATA version 6.0.
Detection of respiratory viruses
In the group of children under 2 years of age, respira-
tory viruses were detected in 60.8% (45 of 74) wheezing
infants and in 13.3% (4 of 30) control infants (P < .001).
RSV was detected in 39% wheezing children and none of
the control infants (P < .001). Rhinovirus RNA was found
in 20.2% and 10% of the wheezing and control children,
respectively (P = .21). Adenovirus was cultured from
29.4% (15/51) of wheezing children and 20.8% (5/24) of
control children; 4 and 1 isolates were identified as sub-
genus B (7.8% and 4.1%), respectively (P = .55). Corona-
virus RNA was found in 3 of 73 wheezing subjects and
none of 30 control subjects. Influenza A and B and
parainfluenza viruses were not detected (Fig 1). Five
wheezing children were positive for more than one virus.
In the group of children 2 to 12 years of age, respira-
tory viruses were not significantly associated with
wheezing. Rhinovirus RNA was detected in 19.3%
wheezing children as compared with 17.1% of the non-
wheezing control children (P = .80); RSV antigen was
detected in 10.3% and 8.5%, respectively (P = .70), and
adenovirus was isolated from 23% (9/39) and 17.8%
(5/28), respectively; 4 and 0 (10.5% and 0%) of the ade-
novirus isolates were identified as subgenus B (P = .07).
Coronavirus, influenza A and B, and parainfluenza virus-
es were not found in children older than 2 years (Fig 1).
Relation of wheezing, IgE response, and
In children under 2 years of age, geometric mean
(GM) total IgE levels were 19.7 IU/mL (range <2 IU/mL
to 1709 IU/mL) in wheezing infants and 9.4 IU/mL
(range < 2 IU/mL to 620 IU/mL) in control infants (P =
.09). Only four wheezing infants, all over 1 year old, pre-
sented IgE antibodies to inhalant allergens: three to mites
and one to mites, dog, and egg; three of these had a
reported history of allergy in both mother and father.
Both wheezing and control infants presented IgE to
foods: 8.9% (6 of 67) and 11.1% (3 of 27) were sensi-
tized to at least one food allergen, respectively (P = .74).
The most common allergens were egg and cow’s milk,
followed by wheat and soy. No sensitization to peanut or
fish was found. IgE to Ascaris lumbricoides was not
detectable in children under 2 years of age. No signifi-
FIG 1. Viral identification in nasal washes by age group. Pink bars indicate nasal washes positive for RSV
antigen; dark yellow bars represent nasal washes positive for rhinovirus; green bars indicate nasal washes
positive for adenovirus B; and light yellow bars represent nasal washes positive for coronavirus. Other com-
mon viral pathogens (influenza A and B and parainfluenza viruses) were not detected. ***P < .001 for wheez-
ing versus control subjects in age group.
554 Camara et al
J ALLERGY CLIN IMMUNOL
cant differences in peripheral blood eosinophil counts
were observed in the wheezing and control groups (GM
= 218/mm3and 208/mm3, respectively) (P = .21).
In children older than 2 years, GM value of total IgE
was 278 IU/mL (range, 7.9 to 2627 IU/mL) in wheezing
children and 97.4 IU/mL (range, 2.0 to 1067 IU/mL) in
control children (P = .002). Sensitization to inhalant
allergens was present in 72.4% of wheezing children and
42.8% of control children (P = .005). Mites and cock-
roach were the sensitizing allergens associated with
wheezing. Specific IgE to A lumbricoides was more fre-
quently found in wheezing children, 33.9% (19 of 56) as
compared with 14.2% (5 of 35) of the control children (P
= .04). Peripheral blood eosinophil counts were higher but
did not reach significance (GM = 350/mm3and 199/mm3
in wheezing and control children, respectively) (P = .08).
Role of allergen exposure
Concentrations of mite, cockroach, cat, and dog aller-
gens in dust samples of homes of wheezing children and
control children were compared (Table I). Levels of
group 2 mite allergens were significantly higher in
homes of wheezing children under 2 years of age. Levels
of group 1 mite allergens, Bla g 1 and Bla g 2, Fel d 1,
and Can f 1, in the homes were not different between
wheezing and control children for either age group
(Table I). The highest levels of mite allergens were found
in bedding samples.
Analysis of risk factors for wheezing
Infection with respiratory viruses, particularly with
RSV, was the major risk factor for wheezing among chil-
dren younger than 2 years of age, as revealed by univari-
ate analysis. Personal and family history of allergy were
both significantly associated with wheezing (Table II). In
the multivariate model, viral infection and family history
of allergy were each independently associated with
wheezing, and sensitization to inhalant allergens played
no significant role in wheezing in infants (Table III).
Among children 2 to 12 years old, allergy was the most
important risk factor for wheezing, indicated by the high-
er frequency of positive tests for specific IgE to inhalant
allergens and elevated total IgE levels (Table II). IgE to A
lumbricoides and personal history of allergy were both
associated with wheezing (Table II). On the other hand,
viral infection was not a significant risk factor for wheez-
ing in this age group. Two models of multivariate analysis
were generated by using levels of specific IgE antibodies
≥ 0.7 kUA/L or ≥ 3.5 kUA/L (considered as high level). In
both models, sensitization to inhalant allergens was the
major independent risk factor for wheezing (Table IV).
Current exposure to high levels of indoor allergens was
not significantly associated with wheezing (Table I). Levels
of group 1 mite allergens >10 µg/g of dust were found in
approximately 70% of the homes of children older than 2
years and in 36% to 46% of the homes of children under 2
years, with no differences between wheezing and control
groups. Approximately 25% of homes presented high levels
of cockroach allergens in dust samples. In 13 of 172 (7.5%)
homes,cats were present in the house. Levels of cat allergen
were undetectable or very low in the majority of samples;
however, Fel d 1 levels in homes with cats were higher than
in those without a cat (GM = 1.06 µg/g and 0.19 µg/g, P <
.0001). The presence of dogs was found in 87 of 172
(50.2%) homes visited, and Can f 1 levels were also higher
in homes with dogs as compared with homes without dogs
(GM = 6.4 µg/g and 0.5 µg/g, P < .0001). No synergistic
effect was observed when the combination of sensitization
and exposure to specific allergens was analyzed.
No association of passive smoke exposure and wheez-
ing was found (Table II). Breast-feeding for at least 6
months was reported for 21.4% (12 of 56) of wheezing
children older than 2 years of age as compared with
31.4% (11 of 35) of control children (P = .28).
Health care delivery
TABLE I. Median levels and range (in parenthesis) of major allergens from mites, cockroach, cat, and dog in dust sam-
ples of homes of wheezing and control children by age group
Under 2 y2 to 12 y
Allergens Wheeze (n = 65)Control (n = 25)P valueWheeze (n = 51)Control (n = 29)P value
Group 1 mite allergens (µg/g of dust) 9.6 9.2 .5 16.7† 28.3‡
(1.5 to 131)
(0.2 to 39.4)
(0.7 to 25.9)
(0.028 to 1.82)
(0.06 to 3.0)
(0.07 to 267.4)
(0.05 to 200.7)
(0.1 to 191.6)
(0.7 to 35.2)
(0.028 to 1.11)
(0.06 to 23.7)
(0.01 to 200)
(0.9 to 56.6)
(0.1 to 12.1)
(0.7 to 42.4)
(0.028 to 1.38)
(0.06 to 2.6)
(0.1 to 76.8)
(1.2 to 654.4)
(0.1 to 90.0)
(0.7 to 86.4)
(0.028 to 1.58)
(0.06 to 23.1)
(0.04 to 194.5)
Group 2 mite allergens (µg/g of dust) .01.7
Bla g 1 (U/g of dust) .2.5
Bla g 2 (µg/g of dust).1 .5
Fel d 1 (µg/g of dust)* .2 .4
Can f 1 (µg/g of dust)* .9 .4
*Presence of cats or dogs was found in 13 of 172 (7.5%) and 87 of 172 (50.2%) homes visited, respectively. In most cases, animals were kept outside the
†P < .05 compared with wheezing children under 2 years of age.
‡P < .05 compared with control children younger than 2 years of age.
§P < .05 compared with wheezing children under 2 years of age.
J ALLERGY CLIN IMMUNOL
VOLUME 113, NUMBER 3
Camara et al 555
In the current study, we have identified for the first time
risk factors associated with acute wheezing among chil-
dren living in a subtropical area of South America. We
have found that RSV infection was strongly associated
with wheezing among children under 2 years of age.7,12
The frequency of RSV was lower than that reported in
temperate regions (39% versus 60% to 80%).7 However,
if we consider the subgroup of infants 0 to 6 months old,
61% tested positive for RSV antigen. RSV infections
were predominantly found in the months of February to
May, corresponding to late summer and early to mid-fall,
indicating that the virus occurs in a different seasonal pat-
tern as compared with that of the northern hemisphere.
The available data indicate that the main age group affect-
ed by RSV in developing countries is children under 6
months of age and that in tropical or subtropical climates
RSV outbreaks are frequently associated with the rainy
season.23 Household and day care–based prospective
studies in coastal northeast Brazil have identified RSV at
an unexpectedly low frequency, 0% to 4%.24,25 A previ-
ous study in Ribeirão Preto, analyzing samples of 829
children under 5 years of age with nonspecific respirato-
ry tract symptoms seen in the ED revealed that RSV was
present in 21.6% of nasal washes. However, the vast
majority of RSV infections (157/188 episodes, 83.5%)
were found in children under 1 year of age.26
Health care delivery
TABLE II. Univariate analysis of risk factors for acute wheezing among children 0 to 12 years old
Under 2 y 2 to 12 y
(n = 74)
(n = 30)
(n = 58)
(n = 35)
(95% CI)Risk factorP valueP value
Age in mo (median)
Male sex (%)
Personal history of
Family history of
Total serum IgE ≥400
Sensitization to inhalant
Sensitization to food
Specific IgE to Ascaris
Viral infection (%)‡
High-level exposure§ to:
64 1.0 (0.9 to 1.0)
0.8 (0.3 to 1.9)
3.3 (1.04 to 10.5)
0.9 (0.9 to 1.0)
1.1 (0.5 to 2.8)
24 (7.3 to 81.0)
72.9 46.6 3.0 (1.2 to 7.4).0165.5 62.81.1 (0.4 to 2.6) .79
4.1 3.41.2 (0.1 to 12.0) .844.822.8 2.7 (1.06 to 7.0) .03
5.40—— 72.442.83.5 (1.4 to 8.4) .005
403.3 (1.3 to 8.0)
12.1 (1.5 to 96.6)
0.9 (0.1 to 5.7)
n.d. 11.1 0.7 (0.1 to 3.4)
00——33.9 14.23.0 (1.02 to 9.2) .04
10.0 (2.9 to 37.9)
2.0 (0.8 to 4.9)
1.4 (0.5 to 3.5)
1.5 (0.6 to 3.5)
1.6 (0.6 to 4.1)
0.7 (0.2 to 2.1)
0.7 (0.2 to 2.7)
0.8 (0.3 to 2.2)
1.0 (0.3 to 3.0)
1.0 (0.4 to 2.9)
*Levels of specific IgE antibodies ≥0.7 kUA/L (CAP class ≥2) to at least one inhalant allergen (mite, cockroach, cat, or dog) or food allergen (egg, milk, soy,
wheat, fish, or peanut).
†Levels of IgE antibodies to A lumbricoides ≥0.7 kUA/L (CAP class ≥2).
‡Detection of RSV antigen, rhinovirus RNA, adenovirus B, and/or coronavirus RNA in nasal washings.
§High-level exposure to mites, cockroach, cat, and dog were defined as group 1 mite allergen levels ≥10 µg/g of dust; cockroach allergens Bla g 1 ≥8 U/g or
Bla g 2 ≥0.32 µg/g of dust; cat allergen Fel d 1 ≥8 µg/g of dust; and dog allergen Can f 1 ≥10 µg/g of dust, respectively, at least in one site of the home.
n.d., Not done. IgE to food allergens was not assayed on children ages 2 to 12 years; —, odds ratios for variables with a zero value could not be calculated
with STATA 6.0.
TABLE III. Multivariate analysis of risk factors for wheezing in children under 2 years of age
Risk factor Wheeze (%) n = 74Control (%) n = 30Odds ratio (95% CI)P value
Family history of allergy†
Sensitization to inhalant and/or food allergens*
15.5 (4.0 to 60.5)
4.2 (1.4 to 12.4)
1.3 (0.2 to 6.5)
0.9 (0.3 to 2.7)
*Detection of rhinovirus RNA, coronavirus RNA, adenovirus B, and/or RSV antigen in nasal washings.
†History of asthma, rhinitis, and/or atopic dermatitis in parent(s) and/or siblings.
‡Sensitization defined as IgE antibody levels ≥0.7 kUA/L (CAP class ≥2) to at least one inhalant allergen (mites, cockroach, cat, dog) or food allergen (egg,
milk, soy, wheat, fish, or peanut).
556 Camara et al
J ALLERGY CLIN IMMUNOL
The lack of evidence for association of rhinovirus and
wheezing in the current study is striking. It is possible
that genetic factors may play a role in determining
immunologic responses to rhinovirus in different popula-
tions. In addition, rhinovirus serotypes circulating in
tropical areas may be different from those in temperate
climates, particularly regarding their ability to replicate
in the lower respiratory airways. Temperatures in the
lower airways may be critical for the intensity of replica-
tion, at least for some rhinovirus serotypes.27 It has been
demonstrated that inhalation of cold air results in sub-
stantial temperature decrease in the lower airways28 that
may favor rhinovirus replication. In the northern hemi-
sphere, rhinovirus peak prevalence occurs in early fall
and late spring and has been associated with new school
terms.29 In subtropical climates, it is possible that higher
temperatures year-round may be less conducive to pro-
ductive growth of rhinovirus. Reduced rhinovirus spread
in these areas could, at least in part, be due to the styles
of housing peculiar to warmer climates, with homes and
schools being ventilated by keeping windows open.
The role of adenovirus in causing wheezing and per-
sistent asthma in children is largely unknown. It has been
suggested that latency of adenovirus in infected lung
epithelial cells is associated with amplification of ciga-
rette smoke–induced inflammation and may cause aller-
gen-induced eosinophilic inflammation to become steroid
resistant.30 Adenoviruses play an important role as a
cause of lower respiratory infections among children in
Argentina and Chile,31,32 being secondary only to RSV.
Similar to previous studies,12,33-35 sensitization to
inhalant allergens was the major independent risk factor
for wheezing among children 2 to 12 years of age, and
home exposure to high levels of inhalant allergens was
not associated with current wheezing. We have previous-
ly reported that mites and cockroach were major causes of
sensitization among children with asthma and/or allergic
rhinitis, seen at university-based allergy clinics in
Ribeirão Preto and São Paulo, Brazil.36 In the current
study, the frequency of allergic sensitization was very
high, notably among control children (43% of the chil-
dren). Part of the reason for finding a higher-than-expect-
ed frequency of sensitization among control subjects may
be due to the fact that we have not aimed to exclude sub-
jects with allergic rhinitis from the control group. It would
be difficult to have a definitive diagnosis of allergic rhini-
tis among children with respiratory distress at the ED set-
ting. It is possible that some subjects with allergic rhinitis
may have been included as control subjects, particularly
in the group of children older than 2 years of age.
The relation of asthma and allergy with parasitic infec-
tion is controversial. Our studies in children living in
poverty in northeast Brazil have shown that current infec-
tion with A lumbricoides was an independent risk factor
for wheezing, in addition to positive skin tests to inhalant
allergens.37 A study of 2164 children 8 to 18 years of age
from China revealed that infection with A lumbricoides
was associated with increased risk of asthma and with
sensitization to common inhalant allergens.38 On the
other hand, studies in rural Africa point to an inverse cor-
relation between helminthic infections and atopy and
asthma.39 Medeiros et al40 have recently shown that sub-
jects from a Schistosoma mansoni endemic area in Brazil
had lower frequency of skin test positivity to indoor aller-
gens and a milder course of asthma than individuals with
asthma not living in an area endemic for S mansoni. In
the current study, we have found that IgE antibodies to A
lumbricoides were more frequently found in wheezing
children than in control children; however, this associa-
tion was no longer significant after multivariate analysis.
In conclusion, results of the current study have shed
light on risk factors associated with acute wheezing in
children living in a subtropical environment,an area where
the prevalence of asthma is comparable with that in the
United States and other developed countries.41 Wheezing
in the prior 12 months, which has been shown to correlate
better with diagnosis of asthma in Brazil,42 was reported in
22.5% and 16.7% of children 6 to 7 years old and 13 to 14
years old, respectively, evaluated by the ISAAC question-
naire.41 Some of the risk factors for acute wheezing iden-
tified in the current study, including RSV infections in the
first 2 years of life, are similar to those previously report-
ed in studies carried out in temperate developed countries.
Inhalant allergens appear to be a major cause of asthma
Health care delivery
TABLE IV. Multivariate analysis of risk factors for wheezing in children 2 to 12 years of age (model 1 and model 2)
Model 1 Model 2
Risk factorWheeze (%) (n = 58) Control (%) (n = 35) Odds ratio (95% CI)P valueOdds ratio (95% CI)P value
Sensitization to inhalant
allergens (IgE ≥0.7 kUA/L)*
Sensitization to inhalant
allergens (IgE ≥3.5 kUA/L)*
Family history of allergy‡
Specific IgE to Ascaris
lumbricoides (IgE ≥0.7 kUA/L)§
42/58 (72.4) 15/35 (42.8)2.7 (1.06 to 7.1).03——
36/58 (62)7/35 (20)—— 5.7 (1.9 to 16.7).001
1.3 (0.4 to 3.6)
1.1 (0.4 to 3.0)
2.1 (0.6 to 7.2)
1.1 (0.4 to 2.9)
1.0 (0.4 to 2.9)
1.5 (0.4 to 5.4)
34/58 (58.6)22/35 (62.8)1.1 (0.4 to 3.0) .71.1 (0.4 to 2.9) .8
*Sensitization defined as IgE antibody levels ≥0.7 kUA/L (model 1) or IgE antibody levels ≥3.5 kUA/L (model 2) to at least 1 inhalant allergen (mites, cock-
roach, cat, dog).
†Detection of rhinovirus RNA, coronavirus RNA, adenovirus B, and/or RSV antigen in nasal washings.
‡History of asthma, rhinitis, and/or atopic dermatitis in parent(s) and/or siblings.
§Positive specific IgE defined as IgE antibody levels ≥0.7 kUA/L to Ascaris lumbricoides.
J ALLERGY CLIN IMMUNOL
VOLUME 113, NUMBER 3
Camara et al 557
attacks in this environment,and rhinovirus does not appear
to play a remarkable role in triggering asthma symptoms,
as previously described in temperate regions.
The authors wish to thank Gustavo F. Pacca, MD, and the Pedi-
atric residents of Santa Lydia hospital for help with enrolling of the
patients; Heloisa Bettiol, MD, for assistance with statistical analy-
sis; and Maria Lucia da Silva, BSc, for technical assistance.
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