Cat and dog ownership during/after the first year of life and
risk for sensitization and reported allergy symptoms at age 13
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Citation for the original published paper (version of record):
Al-Tamprouri, C., Barman, M., Bill, H. et al (2019)
Cat and dog ownership during/after the first year of life and risk for sensitization and
reported allergy symptoms at age 13
Immunity, Inflammation and Disease
http://dx.doi.org/10.1002/iid3.267
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Received: 9 October 2018
|
Revised: 7 June 2019
|
Accepted: 10 June 2019
DOI: 10.1002/iid3.267
ORIGINAL ARTICLE
Cat and dog ownership during/after the first year of life
and risk for sensitization and reported allergy symptoms
at age 13
Chaifa Al‐Tamprouri1
|
Barman Malin2
|
Hesselmar Bill3
|
Bråbäck Lennart4
|
Sandin Anna1
1
Department of Clinical Science,
Paediatrics, Umeå University,
Umeå, Sweden
2
Department of Biology and Biological
Engineering, Food and Nutrition Science,
Chalmers University of Technology,
Gothenburg, Sweden
3
Department of Paediatrics, Institute
of Clinical Sciences, Sahlgrenska
Academy, University of Gothenburg,
Gothenburg, Sweden
4
Section of Sustainable Medicine,
Department of Public Health and
Clinical Medicine, Umeå University,
Umeå, Sweden
Correspondence
Chaifa Al‐Tamprouri, Department of
Clinical Sciences, Paediatrics, Umeå
University, SE‐901 87 Umea, Sweden.
Email: chaifa.al-tamprouri@umu.se
Abstract
Background: Avoidance of pets as a strategy for preventing atopic diseases has
been questioned. This study aimed to identify the risk of sensitization and
allergic symptoms at age 13 in relation to dog‐ and cat‐keeping during and after
the first year of life.
Methods: The study included all children born at Östersund Hospital in
Northern Sweden between February 1996 and January 1997 (n = 1231). At
inclusion, parents were asked to answer questionnaires about lifestyle,
including cat‐ and dog‐keeping. Dog allergy, cat allergy, hay fever, and
asthma were diagnosed based on parental reported allergic symptoms at 13
years of age (n = 834). The risks of sensitization or allergy in relation to dog‐
and cat‐keeping during and after the first year of life were analyzed with
logistic regression. To adjust for reverse causation, all subjects that had
reported avoidance of pets due to allergic symptoms of the child or allergy in
the family (n = 177) were excluded.
Results: Dog‐ or cat‐keeping during the first year of life reduced the risk of
sensitization to dog or cat allergens, respectively, and to birch and to at least one
of the 10 allergens tested. Cat‐keeping, both during and after the first year of
life, reduced the risk of cat allergy and hay fever. Having a dog at home during
the first year of life reduced the risk of dog and cat allergy, whereas dog‐keeping
after the first year of life did not affect allergic symptoms.
Conclusions: Cat ownership, either during or after the first year of life, may be
a strategy for preventing the development of cat allergy and hay fever later in
life. Dog ownership reduced the risk of sensitization to dog and birch allergen,
and also the risk of cat and dog allergy, but had no effect on hay fever.
KEYWORDS
allergic symptoms, asthma, birth cohort, cat‐keeping, dog‐keeping, sensitization
----------------------------------------------------------------------------------------------This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided
the original work is properly cited.
© 2019 The Authors. Immunity, Inflammation and Disease Published by John Wiley & Sons Ltd.
Immun Inflamm Dis. 2019;1-8.
wileyonlinelibrary.com/journal/iid3
|
1
2
|
1
AL‐TAMPROURI
|
INTRODUCTION
Allergic diseases have increased drastically in Western
countries during the past decades. One possible explanation
for this is provided by the hygiene hypothesis, which states
that a reduced exposure to microorganisms early in life
might increase the risk of developing allergic diseases.1-3 In
line with this hypothesis, studies have shown that children
living on livestock farms have a lower prevalence of
asthma,4 rhinoconjunctivitis, and sensitization5,6 than other
children from the same area. Also, children in regular
contact with farms present fewer symptoms of asthma and
allergy.7 Other lifestyle and environmental factors that may
affect the risk of allergy are the number of older siblings,
lifestyle, socioeconomic status, and frequency of infections.8,9 Having pets at home has also been suggested to
reduce the risk of allergy in both children8,10-12 and
adults.13 However, the impact of cat and dog ownership
on sensitization and the development of allergic symptoms
is still debated. Cat‐keeping has been reported both to
decrease8,12 and increase14 the risk of sensitization development. Also, cat‐keeping has been found to be inversely
correlated to sensitization to cat allergens and to asthma
development.12 Dog‐keeping at home during early childhood has been directly associated with less sensitization and
inversely associated with asthma later in life.8,10,14
Early sensitization to food and inhaled allergens is one
of the risk factors for the development of atopic eczema and
allergy, a risk factor that can be affected by early preventive
strategies.15,16 Another risk factor for asthma 17 and allergic
symptoms is a parental history of allergy.18 Persistence or
remission of asthma during childhood is determined by
sex, asthma phenotype, and level of sensitization.19 It has
also been suggested that the immune system needs the
right incentives and a strong immune stimulation during
infancy to mature and develop tolerance towards harmless
allergens.20,21
By having access to a prospective birth cohort, we
were able to study the relationship between dog‐ and cat‐
keeping during and after the first year of life and the
development of sensitization and allergic symptoms at 13
years of age. The aim of this study was to quantify and
analyze the risk of sensitization, allergy, and allergic
respiratory symptoms at age 13 in relation to dog‐ and
cat‐keeping during the first year of life as well as after the
first year of life.
2
2.1
|
the development of allergy during childhood. The BAS
cohort includes all children living in Jämtland in
northern Sweden and born at Östersund hospital from
February 1996 to January 1997 (n = 1231). Families were
enrolled either at their antenatal clinic or at delivery.
Parents answered questionnaires when their child was
one (n = 1043, 85%) and 13 (n = 834, 68%) years of age.
Questions asked about pet keeping, symptoms of asthma
and other allergies, allergy treatments, and whether the
household avoided pet keeping due to allergy among other
family members.10,22 Questions related to allergy symptoms were based on the International Study of Asthma
and Allergies in Childhood questionnaire (ISAAC).23
2.2
|
Selection of subjects
The population analyzed in this paper include all
children who participated in follow‐up at both one and
13 years of age (n = 834) (Figure 1). Altogether, 252 of
833 (30%) of the families had dogs and 179 of 833 (22%)
had cats at home during the child’s first year of life. Of
those that had a dog or a cat at home during the first year
of life, 77 subjects had both cat and dog at home. See
Table 1 for more characteristics.
2.3
|
Skin‐prick test
Skin‐prick tests (SPTs) were performed at 1, 4, and 13
years of age. One nurse (always the same) performed all
SPTs on the volar aspect of the lower arm at 1 (n = 1040)
and 13 (n = 788) years of age. The test panel included cat,
birch, timothy, egg, and milk at 1 year of age and was
extended to also include dog, horse, soy, wheat, and fish
at 13 years of age. Histamine dihydrochloride 10 mg/mL
was used as a positive control. Children were instructed
to avoid antihistamines for 72 hours before the test.
METHODS
|
Study design
The BAS cohort (BarnAllergiStudien or Paediatric
Allergy Study) was designed to prospectively investigate
ET AL.
FIGURE 1
Flow chart of the study population
AL‐TAMPROURI
|
ET AL.
T A B L E 1 Characteristics of the study population (n = 834a)
Number Percent
Characteristicsb
Sex (boys)
407/809
50
484/782
62
93/771
12
Maternal asthma
114/830
14
Maternal hay fever
168/829
20
Older sibling
Maternal smoking
c
Heredityd
Paternal asthma
Parental hay fever
Asthma at 13 years of age was defined as parental
reported respiratory symptoms during the last 12
months, and/or asthma medication, and/or asthma
diagnosed by a doctor.
Dog allergy at 13 years of age was defined as parental
reported symptoms of rhinoconjunctivitis or respiratory
difficulties upon contact with dogs or dog allergens.
Cat allergy at 13 years of age was defined as
parental reported symptoms of rhinoconjunctivitis or
respiratory difficulties upon contact with cats or
cat allergens.
95/819
12
163/819
20
460/833
55
2.6
179/833
22
194/833
23
375/833
45
252/833
30
206/833
25
Avoidance of pet keeping, based on answers to the
questionnaire administered at 13 years, was defined as
an affirmative answer to the question: “Have you actively
avoided pet keeping due to allergies or asthma in other
family members?” All families that answered affirmatively (n = 177) were excluded from the logistic regression analyses in which cat‐ or dog‐keeping were used as
exposure variables.
Cat‐keepingd
Never cat
Cat‐keeping during first year of life
e
Cat‐keeping only after first year of lifef
Dog‐keepingd
Never dog
Dog‐keeping during first year of life
e
f
Dog‐keeping only after first year of life
a
Included in the statistical analyses were those infants that had participated
in the follow‐ups at both one and 13 years of age (see Figure 1).
b
Information about sex, siblings, and maternal smoking was collected at 1
year of age.
c
When the child was 1 year of age.
d
Information about heredity and cat/dog‐keeping was collected at 13 years of age.
e
Cat/dog‐keeping during the first year of life is regardless of cat/dog‐keeping
after the first year of life.
f
Cat/dog‐keeping only after the first year of life, that is, no cat/dog‐keeping
during the first year of life.
2.4
|
Definitions of exposure variables
Dog‐ or cat‐keeping during the first year of life was defined
as dog or cat ownership during the child’s first year,
regardless of cat or dog ownership after the first year.
This information was collected via questionnaires distributed at 13 years of age.
Dog‐ or cat‐keeping after first year was defined as dog
or cat ownership any time during the period between one
and 13 years of age, but not before 1 year of age. This
information was collected via questionnaires distributed
at 13 years of age.
2.5
|
3
Outcome definitions
Sensitization at 13 years of age was defined as a positive
SPT for a specific allergen if the mean wheal diameter
was at least 3 mm after 15 minutes.
Hay fever at 13 years of age was defined as a
parental reported allergic reaction identified by itchy
eyes and/or runny nose and sneezing upon contact
with pollen allergens.
2.7
|
|
Reverse causation
Statistical analyses
Our study is based on questionnaire responses from a
prospective birth cohort study10,22 in which data were
coded and analyzed using SPSS statistics software (IBM
SPSS statistics data editor, version 22). Odds ratios
(OR) were calculated to study the association between
exposure (cat‐ or dog‐keeping, paternal hay fever,
paternal asthma, maternal hay fever, maternal asthma)
and outcome (sensitization and occurrence of allergic
diseases at 13 years of age). Statistical significance was set
at the 5% probability level. The logistic regression
analysis was carried out using both crude models without
adjustments and models adjusted for the following
potential covariates: paternal hay fever, paternal asthma,
maternal hay fever, maternal asthma, maternal smoking,
older siblings, sex, dog‐ and cat‐keeping. Sensitivity
analyses based on parental allergy were performed for
cat‐ and dog‐keeping during the first year of life to
analyze a potential effect modification of maternal and/or
paternal allergy on sensitization and allergy in the child.
Maternal asthma and/or hay fever was reported for 221 of
the 834 infants while paternal asthma or hay fever was
reported for 209 of the infants. Any paternal or maternal
asthma or hay fever was reported for 370 of the infants
whereas 464 did not report parental allergy. Questions
about heredity, smoking, and older siblings were asked at
1 year of age.
4
|
AL‐TAMPROURI
|
2.8
Ethical aspects
The Ethics Committee at the University of Umeå,
Sweden, approved the study (Nr. 95‐149, 2009‐1116‐31
and 2012‐163‐32M). Written consent from the parents
was required, and at 13 years of age, the child answered
the questionnaire together with the parents and verbally
approved all tests before proceeding with the SPTs.
|
3
3.1
RESULTS
|
Sensitization at 13 years of age
Sensitization to airborne allergens was common at 13 years
of age (Table 2). The prevalence rate of at least one positive
SPT at 13 years was 32%. The corresponding rates previously
reported at 1 and 4 years were 7% and 13%, respectively.10
3.2 | Sensitization at 13 years of age in
relation to dog‐ and cat‐keeping
Dog‐keeping during the first year of life reduced the risk
of sensitization to dog allergen, adj. odds ratio (OR) 95%
confidence interval (CI): 0.18 (0.08‐0.44), birch allergen
(adj. OR [95% Cl]: 0.53 [0.29‐0.98]), and any allergen (adj.
OR [95% Cl]: 0.58 [0.37‐0.92]). Dog‐keeping, not until
after the first year of life, reduced the risk of dog and cat
sensitization (Table 3).
Similarly, cat‐keeping during the first year of life
reduced the risk of sensitization to cat allergen (adj. OR
[95% CI]: 0.50 [0.27‐0.95]), birch allergen (adj. OR [95%
CI]: 0.43 [0.22‐0.84]), and any allergen (adj. OR [95% CI]:
0.58 [0.35‐0.94]). Cat‐keeping, not until after the first year
T A B L E 2 Sensitization to 10 selected allergens at 13 years of age
Allergen
Positive SPTa
%
Number of tested subjects
788
100
Any allergensb
249
32
Timothy
161
19
Cat
140
17
Birch
133
16
Horse
97
12
Dog
81
10
Soy
9
1
Wheat
9
1
Fish
8
1
Egg
7
1
Milk
7
1
Abbreviation: SPT, skin‐prick test.
a
Number of children in the cohort with a positive SPT to the allergen.
b
Positive SPT to one or more of the 10 tested allergens.
ET AL.
of life, reduced the risk for sensitization to the cat, dog,
birch, and any allergen (Table 3).
3.3 | Allergy at 13 years of age in
relation to dog‐ and cat‐keeping
Dog‐keeping, during the first year of life, reduced the risk of
both dog (adj. OR [95% CI]: 0.33 [0.14‐0.76]) and cat (adj.
OR [95% CI]: 0.33 [0.17‐0.64]) allergy, whereas dog‐keeping,
later in life, did not reduce the risk of allergy symptoms.
Cat‐keeping, during the first year of life, reduced the risk of
cat allergy (adj. OR [95% CI]: 0.43 [0.22‐0.85]) and hay fever
(adj. OR [95% CI]: 0.40 [0.21‐0.78]). Cat‐keeping, after the
first year of life, reduced the risk of dog allergy (adj. OR
([95% CI]: 0.35 [0.13‐0.93]), cat allergy (adj. OR [95% CI]:
0.38 [0.19‐0.77]), and hay fever (adj. OR [95% CI]: 0.30
[0.15‐0.62]; Table 4). Asthma at 13 years of age was not
related to cat‐ or dog‐keeping at any time during childhood
(Table 4). To take reverse causation into account all infants
whose parents had answered that they actively avoided pet
keeping due to allergies or asthma in other family members
were excluded from the logistic regressions.
The association between cat and dog‐keeping and
allergy was similar in the crude unadjusted logistic
regression models and in the logistic regression models
adjusted for paternal hay fever, paternal asthma, maternal hay fever, maternal asthma, maternal smoking, older
siblings, sex, and dog‐ and cat‐keeping (Table 4), which
suggests that the association was present even when
controlling for these factors.
To validate the effect of early cat‐ or dog‐keeping on
sensitization and allergy further, sensitivity analyses were
performed where the infants were stratified according to
parental allergy. When comparing the number of infants
with sensitization or allergy at 13 years of age according to
early pet keeping the same associations were seen both for
the 464 infants without, and for the 370 infants with,
parental heredity to allergy. For example, in the group of
infants with no parental allergy, among infants with no
cat‐keeping 37 (16%) had hay fever at 13 years of age while
among infants who had been exposed to a cat at home
during the first year of life six (5%) had hay fever at 13 years
of age. For the group of infants with paternal allergy, the
numbers were 72 (31%) vs 8 (13%), respectively.
3.4 | Sensitization and allergy at 13
years of age in relation to maternal and
paternal heredity
Parental hay fever doubled the risk of sensitization to dog,
cat, birch, and to any allergen at 13 years of age (Table 3).
This is in contrast to parental asthma which did not
significantly alter the risk of sensitization at 13 years of age
AL‐TAMPROURI
|
ET AL.
5
T A B L E 3 Sensitization to dog, cat, birch, and any allergen at 13 years of age in relation to the parental history of asthma and hay fever,
and to pet ownership
Pos SPT to dog at 13 y (n = 81)
Crude OR
(95% CI)
P crude
Adj ORb
(95% CI)
Paternal hay fever
2.51 (1.53‐4.10)
<.001
2.22 (1.30‐3.87)
Paternal asthma
2.09 (1.15‐3.80)
.016
Maternal hay fever
2.08 (1.26‐3.42)
.004
Maternal asthma
1.74 (0.98‐3.10)
.06
Pos SPT to cat at 13 y (n = 140)
Crude OR
(95% CI)
P crude
Adj ORb
(95% CI)
P adjusted
.005
2.28 (1.51‐3.43)
<.001
2.42 (1.53‐3.85)
<.001
1.44 (0.73‐2.86)
.294
1.36 (0.80‐2.33)
.26
0.92 (0.50‐1.69)
.792
1.78 (1.01‐3.14)
.047
2.20 (1.46‐3.29)
<.001
2.08 (1.31‐3.31)
.002
1.37 (0.70‐2.65)
.356
1.34 (0.82‐2.20)
.246
1.07 (0.61‐1.87)
.812
P adjusted
Dog‐keepingc
Never
1.0
First year of lifed
0.20 (0.09‐0.46)
<.001
0.18 (0.08‐0.44)
<.001
0.56 (0.33‐0.96)
.034
0.61 (0.35‐1.06)
.081
0.47 (0.24‐0.94)
.032
0.38 (0.18‐0.82)
.014
0.55 (0.31‐0.98)
.044
0.47 (0.25‐0.88)
.018
e
After first year only
1.0
1.0
1.0
Cat‐keepingc
Never
1.0
First year of lifed
0.64 (0.32‐1.27)
.199
0.77 (0.37‐1.60)
.480
0.45 (0.24‐0.81)
.009
0.50 (0.27‐0.95)
.033
0.25 (0.10‐0.65)
.005
0.27 (0.10‐0.74)
.010
0.41 (0.22‐0.76)
.004
0.42 (0.22‐0.80)
.009
e
After first year only
1.0
1.0
Pos SPT to any allergena at 13 y (n = 251)
Pos SPT to birch at 13 y (n = 133)
Crude OR
(95% CI)
P crude
Adj ORb
(95% CI)
1.0
P adjusted
Crude OR
(95% CI)
P crude
Adj ORb
(95% CI)
P adjusted
Paternal hay fever
1.87 (1.23‐2.86)
.004
1.81 (1.12‐2.91)
.016
1.96 (1.38‐2.79)
<.001
1.87 (1.25‐2.79)
.002
Paternal asthma
1.28 (0.73‐2.22)
.392
0.84 (0.45‐1.60)
.603
1.40 (0.90‐2.19)
.140
1.07 (0.64‐1.78)
.804
Maternal hay fever
2.66 (1.77‐4.00)
<.001
2.12 (1.36‐3.43)
.001
2.50 (1.76‐3.55)
<.001
2.28 (1.53‐3.42)
<.001
Maternal asthma
1.87 (1.16‐3.01)
.010
1.36 (0.79‐2.35)
.262
1.65 (1.10‐2.48)
.017
1.18 (0.74‐1.89)
.489
Dog‐keepingc
Never
1.0
First year of life
d
After first year onlye
1.0
1.0
1.0
0.52 (0.29‐0.93)
.026
0.53 (0.29‐0.98)
.042
0.55 (0.36‐0.84)
.006
0.58 (0.37‐0.92)
.021
0.74 (0.42‐1.30)
.295
0.77 (0.43‐1.39)
.387
0.73 (0.47‐1.13)
.158
0.69 (0.43‐1.11)
.126
Cat‐keepingc
Never
1.0
First year of life
0.38 (0.20‐0.73)
.004
0.43 (0.22‐0.84)
1.0
.013
1.0
0.50 (0.32‐0.80)
.004
1.0
0.58 (0.35‐0.94)
.028
After first year onlye
0.38 (0.19‐0.72)
.003
0.39 (0.20‐0.77)
.006
0.52 (0.33‐0.82)
.005
0.54 (0.33‐0.87)
.012
Abbreviations: CI, confidence interval; OR, odds ratio; Pos SPT, positive skin‐prick test.
At least one positive SPT when testing 10 different allergens at 13 years of age.
b
After multiple logistic regression adjusting for paternal hay fever, paternal asthma, maternal hay fever, maternal asthma, maternal smoking, older siblings, sex,
and dog‐ or cat‐keeping.
c
After exclusion of all children whose families reported avoiding pet ownership during their first year of life because of asthma or allergies in other family
members (n = 177).
d
Comparing cat/dog‐keeping during the first year of life (regardless of cat/dog‐keeping after the first year of life) with never cat/dog‐keeping from birth to 13 years of age.
e
Comparing cat/dog‐keeping after the first year of life with never cat/dog keeping from birth to 13 years of age.
a
(Table 3). Finally, parental hay fever increased the risk for
the child to develop dog allergy, cat allergy, and hay fever
(Table 4) opposed to parental asthma with no significant
altered risk of allergic reactions to dog, cat, or hay fever but
more than doubled the risk for the child to develop asthma
(Table 4).
4
|
DISCUSSION
Our results suggest that having a dog or a cat at home during
the first year of life, as well as later during childhood, can
reduce the risk of sensitization to common airborne allergens
at age 13. Also, having a dog at home during the first year of
life may reduce the risk of dog and cat allergy, whereas cat‐
keeping, both during and after the first year of life, may
reduce the risk of cat allergy and hay fever at 13 years of age.
The association between dog‐ or cat‐keeping during the
first year of life and a lower risk of sensitization to these
specific allergens at age 13 might partly be explained by the
exposure to a high dose of dog and cat allergens early in life.
This exposure may influence the immune system during
an important time period, called “window of opportunity”, in
6
|
AL‐TAMPROURI
ET AL.
T A B L E 4 Allergic symptoms at 13 years of age in relation to pet ownership, family history of asthma and hay fever (n = 834)
Dog allergy 13 y (n = 76)
Crude OR
(95% CI)
P crude
Cat allergy 13 y (n = 124)
Adj ORa
(95% CI)
P adjusted
Crude OR
(95% CI)
P crude
Adj ORa
(95% CI)
<.001
2.14 (1.34‐3.34)
.002
.022
1.29 (0.71‐2.34)
.398
Paternal hay fever
2.30 (1.34‐3.83)
.001
1.93 (1.08‐3.43)
.026
2.43 (1.560‐3.70)
Paternal asthma
1.85 (0.98‐3.45)
.054
1.24 (0.60‐2.57)
.555
1.84 (1.09‐3.09)
P adjusted
Maternal hay fever
1.82 (1.08‐3.07)
.025
1.57 (0.86‐2.84)
.141
1.86 (1.21‐2.86)
.004
1.66 (1.02‐2.72)
.042
Maternal asthma
1.79 (0.99‐3.22)
.055
1.66 (0.86‐3.22)
.133
1.54 (0.93‐2.55)
.093
1.36 (0.77‐2.40)
.289
Dog‐keepingb
Never
1.0
First year of lifec
0.33 (0.14‐0.74)
.007
1.0
0.33 (0.14‐0.76)
.009
1.0
0.32 (0.17‐0.61)
<.001
0.33 (0.17‐0.64)
1.0
.001
After first yeard
0.50 (0.23‐1.11)
.087
0.45 (0.20‐1.04)
.062
0.66 (0.37‐1.17)
.153
0.59 (0.32‐1.08)
.087
Cat‐keepingb
Never
1.0
First year of lifec
0.60 (0.28‐1.30)
.194
1.0
0.63 (0.28‐1.42)
.263
1.0
0.40 (0.21‐0.78)
.007
0.43 (0.22‐0.85)
.015
After first yeard
0.32 (0.12‐0.86)
.023
0.35 (0.13‐0.93)
.035
0.40 (0.21‐0.78)
.007
0.38 (0.19‐0.77)
.007
Hay fever 13 y (n = 155)
Crude OR
(95% CI)
P crude
1.0
Asthma 13 y (n = 102)
Adj ORa
(95% CI)
P adjusted
Crude OR
(95% CI)
P crude
Adj ORa
(95% CI)
P adjusted
Paternal hay fever
2.40 (1.60‐3.61)
<.001
2.31 (1.45‐3.66)
<.001
1.60 (1.04‐2.45)
.032
1.33 (0.81‐2.18)
.254
Paternal asthma
1.47 (0.87‐2.48)
.151
0.91 (0.49‐1.68)
.761
2.72 (1.68‐4.40)
<.001
2.49 (1.43‐4.35)
.001
Maternal hay fever
2.99 (2.01‐4.445)
<.001
2.87 (1.82‐4.52)
<.001
2.72 (1.82‐4.06)
<.001
1.96 (1.24‐3.12)
.004
Maternal asthma
1.9 (0.98‐2.57)
.060
1.05 (0.61‐1.84)
.852
3.86 (2.49‐5.98)
<.001
2.81 (1.69‐4.65)
<.001
Dog keepingb
Never
First year of life
1.0
c
After first yeard
1.0
1.0
1.0
0.76 (0.45‐1.28)
.306
0.82 (0.47‐1.45)
.503
0.76 (0.45‐1.27)
.299
0.29 (0.04‐3.34)
.245
0.64 (0.35‐1.16)
.141
0.6 7(0.36‐1.28)
.226
0.86 (0‐50‐1.49)
.593
0.89 (0.50‐1.61)
.712
Cat‐keepingb
Never
1.0
First year of lifec
0.36 (0.19‐0.70)
.001
0.40 (0.21‐0.78)
1.0
.007
1.01 (0.60‐1.70)
1.0
.986
1.03 (0.58‐1.82)
1.0
0.028
After first yeard
0.27 (0.13‐0.54)
<.001
0.30 (0.15‐0.62)
.001
0.78 (0.44‐1.36)
.375
0.68 (0.37‐1.26)
0.012
Abbreviations: CI, confidence interval; OR, odds ratio; SPT, skin‐prick test.
a
After multiple logistic regression adjusting for paternal hay fever, paternal asthma, maternal hay fever, maternal asthma, maternal smoking, older siblings, sex,
and dog‐ or cat‐keeping.
b
After exclusion of all children whose families reported avoiding pet ownership during their first year of life because of asthma or allergies in other family
members (n = 177).
c
Comparing cat/dog‐keeping during the first year of life (regardless of cat/dog‐keeping after the first year of life) with never cat/dog‐keeping from birth to 13
years of age.
d
Comparing cat/dog‐keeping after the first year of life with never cat/dog‐keeping from birth to 13 years of age.
which tolerance can be induced.24 However, the time and
mechanism by which tolerance was induced in our subjects
cannot be further speculated on since we have no additional
immunological analyses.
Having a dog or cat at home during the first year of life
also reduced the risk of sensitization to birch allergens at 13
years of age which is in line with our previous report from
the same study population where we described an
association between dog‐keeping during the first year of
life and a reduced risk of sensitization to pollen at 4 years of
age.10 Both these observations from our prospective cohort
study are consistent with results of other longitudinal
studies.8,13,14 Having dogs or cats at home may, in addition
to allergen load, affect other exposures for substances in the
indoor environment such as different bacteria and rate of
microbial turnover. It has been shown that indoor
environments with dogs have higher concentrations of
endotoxins.25 Exposure to endotoxins and other microbial
compounds has been suggested to reduce the risk of atopic
symptoms and of sensitization among children,26 especially
in families with cats and dogs.27 This is in accordance with
another recent observation on early microbial exposure: a
reduced risk of asthma and eczema was observed in
children whose parents cleaned the child’s pacifier in their
own mouth, when dropped on the floor, before giving it
back to the child.1 The authors explained that this reduced
AL‐TAMPROURI
|
ET AL.
risk may be due to the immune stimulation by microbes
transferred to the infant via the parent’s saliva. A similar
microbial impact could be a possible explanation in an
environment with indoor pets and reduced risk of
sensitization due to positive stimulation of the immune
system. This hypothesis is in line with a recent study on
early pet keeping and later allergy development, showing
that the protective effect from cats and dogs is dose‐
dependent, suggesting that cats and dogs induce an allergy‐
protective “mini‐farm” environment.28 How bacterial and
other microbes may modulate immunological activities and
reduce the risk of sensitization and allergic symptoms
need to be further elucidated.
Dog‐ and cat‐keeping during infancy affected the risk of
self‐reported dog or cat allergy at age 13. In addition, cat‐
keeping during the first year of infancy, but not dog‐keeping
during the first year, reduced the risk of hay fever, a highly
hereditary condition induced by pollen from both grass and
trees. Parents with hay fever may hesitate to accept a cat or a
dog at home and to be able to avoid reverse causation we
removed all families who reported avoiding pet ownership
due to allergy symptoms among other family members from
our analyses. To further validate the effect of parental
heredity on the association between early cat‐ or dog‐keeping
on sensitization and allergy, we divided the infants into those
with no parental heredity to hay fever or asthma and those
with either maternal and/or paternal hay fever or asthma
and compared the associations between pet keeping and
sensitization and allergy. The associations were similar in the
two groups suggesting that the effect of early life cat or dog‐
keeping on sensitization and allergy is not modified by
parental heredity to allergy.
Other studies have reported conflicting results regarding
the effects of dog‐ and cat‐keeping on sensitization or allergy
development during childhood. In one study of 399 children,
dog‐ and cat‐keeping during the third trimester of pregnancy
or the first year of life did not show any association with
sensitization or rhinitis.29 In another study with pooled data
from 11 prospective studies, the presence of dogs or cats at
home did not affect the risk of asthma or allergic rhinitis in
children.30 One recent study reported a higher incidence
of dog and cat allergy during the first 4 years of life in
children with early exposure to the respective animal during
infancy.31 This is in contrast to our findings of lower rates of
sensitization and allergy symptoms with either a cat or dog in
the home during the child’s first year and also with a cat in
the home later in childhood but not during infancy.
It is well known that a parental history of allergy is an
important risk factor for asthma, allergic symptoms, and
sensitization.32,33 In this study, we found that parental
asthma increased the risk of asthma in the children, while
parental hay fever increased their risk of hay fever, cat
allergy, and for paternal hay fever even dog allergy.
7
This study has several strengths, including the
prospective birth cohort design with longitudinal follow‐up at specific time‐points, the total area coverage
with inclusion of all children born at Östersund Hospital
during a 1‐year period, the use of validated questionnaires, and the fact that all SPT were carried out by the
same nurse. A limitation of our study may be that allergy
diagnosis was made using parent‐reported questionnaire‐
based symptoms. However, the surveys were based on
questions from the ISAAC study,23 that is, validated and
used in numerous studies over many years.
In conclusion, having a dog or a cat at home during
the first year of life reduced the risk of sensitization and
allergic symptoms to dogs and cats, respectively, whereas
having a cat also reduced the risk of sensitization and
allergic symptoms to birch allergen and hay fever. Cat‐
keeping later during childhood, although not dog‐
keeping, reduced the risk of dog allergy, cat allergy,
and hay fever. Although this is in line with several earlier
studies, more research is needed to understand the
mechanisms behind the allergy‐protective effects associated with the keeping of cats and dogs, early in life.
ACKN OWLEDGMENTS
The authors wish to express their gratitude to Anna
Bernholm for performing all skin‐prick tests, to Robert
Lundqvist for statistical support and to Monica Gio‐Batta
for language editing. The authors thank Viviana Moroso
of MV Medical Writing (Luleå, Sweden) for copy editing
the manuscript, in accordance with Good Publication
Practice guidelines (http://www.ismpp.org/gpp3).
DATA ACCESSIBILITY
The data that support the findings of this study are available
from the corresponding author upon reasonable request.
ORCID
Chaifa Al‐Tamprouri
9754
http://orcid.org/0000-0003-4441-
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How to cite this article: Al‐Tamprouri C,
Barman M, Hesselmar B, Bråbäck L, Sandin A. Cat
and dog ownership during/after the first year of life
and risk for sensitization and reported allergy
symptoms at age 13. Immun Inflam Dis. 2019;1‐8.
https://doi.org/10.1002/iid3.267