RESPIRATORY MEDICINE (1998) 92, 316-324
7- and S-year-old
and related conditions
rates and risk factor pattern
E. RONMARK*+*, B. LUNDBACK*+, E. JONSSON* AND T. PLATTS-MILLS'
“Respirafory Epidemiology Unit, Division of Allergy, Department of Occupational Health,
Nafional Institute for
Working Life, Umek and Solna, Sweden
‘The OLIN Study Group, Deparfmenf of Medicine, Cenfral Hospital of Norrboffen, Lulei-Boden,
*Lulei Healfh Care Cenfre, LuleB Sweden
‘Asthma and Allergic Diseases Center, Deparfmenf of Medicine, University of Virginia,
As a first step in an intervention study of asthma and allergic diseases among school children, a cross-sectional study
was performed during Winter 1996 in three towns (Kiruna, Lules and Pitei) in the northernmost province of
Sweden, Norrbotten. The cross-sectional study aimed to measure the prevalence of asthma, type-l allergy and
allergic diseases in order to make it possible to measure the incidence of the diseases, conditions and symptoms
related to the diseases. Another aim was to perform a screening for possible risk factors. All children enrolled in the
first and second classes at school, 7 and 8 years old, were invited to take part in this study. The ISAAC questionnaire
with added questions about symptoms, morbidity, heredity and environment was distributed by the schools to the
parents. The response rate was 97%, and 3431 completed questionnaires were returned. The children in two of
the municipalities were also invited to skin test, and 2149 (88%) were tested with 10 common airborne allergens. The
results showed that 7% of the children were currently using or had used asthma medicines during the last 12 months.
Six percent had asthma diagnosed by a physician, and 4% were using inhaled corticosteroids. The prevalence of
wheezing during the last 12 months was 12%, rhinitis without colds 14%, and eczema 27%, while 21% had a positive
skin test. The respiratory symptoms and conditions were significantly greater in boys and, further, they were most
prevalent in Kiruna in the very north, though not significantly. Type-l allergy and asthma had different risk factor
patterns. The main risk factors for asthma were a family history of asthma (ORz3.2) followed by past or present
house dampness (OR= 1.9), male sex (OR= 1.7) and a smoking mother (OR= 1.6). In Kiruna, when none of these
three risk factors were present, none of the children had asthma, but when all three were present, 38% of
these children were using asthma medicines.
RESPIR. MED. (1998) 92, 316-324
During the last three to four decades, the prevalence of
asthma and allergic diseases has increased considerably in
many countries, probably due to increased diagnostic inten-
sity, altered diagnostic criteria and also a true increase in
prevalence. Today, asthma and allergic diseases comprises
the greatest group of diseases in children, adolescents and
young adults in many parts of the world. The increase was
first documented in Australia, New Zealand and the U.K.,
countries in which the increase also seems to be most
Received 13 October 1997 and accepted 22 October 1997.
Correspondence should be addressed to: E. Riinmark, The OLIN
Study Group, Lulel Health Care Center, Timmermansgatan 31,
S-972 41 Luleb, Sweden.
pronounced (l-6). Today, high prevalence of asthma and
respiratory symptoms has been shown in children in later
industrialized countries such as Chile (7) and Singapore (8).
Prevalence rates in North America (9,lO) and Europe
(1 l-l 3), particularly Central Europe (7,l l), are generally
low in comparison with Australia and New Zealand.
The incidence of asthma and allergic diseases reaches a
peak in children of school age and younger (6,14-16).
Asthma is strongly associated with type-l allergy (17).
Type-l allergy shows a different sensitization profile in
different environments and in different parts of the world.
The dominating allergens may be pets such as cats or dogs
(10,18), house-dust mites (19,20), pollen (21), moulds (22)
and cockroaches (23,24). In the indoor environment,
tobacco smoke (25-27) and dampness at home (25,27-29)
are associated with an increased risk of asthma in children.
0 1998 W. B. SAUNDERS COMPANY LTD
ASTHMA, TYPE-I ALLERGY AND RELATED CONDITIONS 3 I7
The role of outdoor air pollution as a risk factor for asthma
is controversial (30-32); however, some studies report air
pollution from traffic to be a risk factor for asthma (33-35).
Other potential causes such as diet and respiratory infec-
tions (36) are under debate. Although an increasing number
of studies show similarities in the risk factor pattern for
asthma, there is still no general agreement about why there
has been such a marked increase.
In Sweden, the prevalence of asthma has also increased,
mainly in children (37) adolescents (15,16) and young
adults (38). Comparative studies have pointed out that
asthma is most prevalent in the north of the country
(37,38), where mites and moulds hardly exist and conven-
tional air pollution is low. This area is of particular interest
in studying risk factors of the conditions and causes of the
increasing prevalence of asthma.
An intervention study aiming to reduce the incidence and
morbidity of allergic diseases, mainly asthma, among
school children in Northern Sweden started in 1996. The
aim of this paper is to report prevalence rates of allergic
conditions, mainly asthma, and risk factors for the
Materials and Methods
All school children in the towns and municipalities of
Kiruna, Lulea and Pitea in Norrbotten, the northernmost
province of Sweden, in the first and second classes at school
were invited to take part in this study, which is planned to
last for 8 years. The intervention focused on cleaning of the
schools, active and passive smoking, and to increase the
knowledge of allergy prevention according to a programme
developed by the Swedish Institute of Public Health.
The study started in February-April 1996 with a cross-
sectional survey in order to estimate the prevalence of
asthma, respiratory symptoms, rhinitis, eczema and type-l
allergy, and to screen for risk factors for the conditions.
The study was approved by the Ethical Committee at the
University and the University Hospital of Northern Sweden
The municipalities consist of both urban and rural areas.
Two of them, Lulea and Pitea, are located on the Baltic Sea,
and Kiruna is situated in the inland mountains north of the
Arctic circle (Fig. 1). The climate in the two coastal
municipalities is similar, with an average temperature of
2°C (January - 11°C July 15°C) while the corresponding
value for Kiruna is - 2°C (January - 15°C July 12°C).
The relative humidity varies considerably between winter
and summer. The winter in Kiruna lasts for 7-8 months,
more than 1 month longer than in the coastal areas.
The city of Lulea is the administrative, commercial and
cultural centre of the province, and in 1996, it had 71 000
inhabitants, of which 50 000 lived in the urban area.
Furthermore, it has the largest steel industry in Sweden.
Pitea had 41 000 inhabitants, of which approximately one
half are living in the town of Pitea. Pitea has wood and
FIG. 1. Map of Sweden and the province of Norrbotten
with the towns Kiruna, Lulea and Pitea.
paper-pulp industries. Kiruna includes a large area with
mountains and had 26 000 inhabitants in 1996, of whom
20 000 lived in the town. The biggest iron mine in Western
Europe and airspace research are located to Kiruna.
All 3525 school children enrolled in the first and second
classes were invited to participate in the study. They were
7-8 years old with few exceptions, and 51% were boys. In
all, 20 schools in Kiruna, 35 in Lulea and 26 in Pitea were
enrolled. The study population and the participation rate
are described in Table 1.
A questionnaire with a covering letter explaining the aim of
the study was distributed to the children’s parents by the
school teachers. The response rate was 97%. In Kiruna and
Lulea, the children were invited to have skin prick tests, and
2114 (86%) were tested. In addition, 35 children had been
skin tested prior to the study at the paediatric policlinics in
Kiruna and Lulea. These results [total 2149 (88%)] have
been included in the analysis.
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