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Mahmoud Zureik, Catherine Neukirch, BÈnÈdicte Leynaert,
Renata Liard, Jean Bousquet,
Françoise Neukirch, on behalf of the European Community Respiratory
Health Survey
National Institute of |
Objective To assess whether the severity of
asthma is associated with sensitisation to airborne moulds rather
than to other seasonal or perennial allergens.
Design Multicentre epidemiological survey
in 30 centres.
Setting European Community respiratory health
survey.
Participants 1132 adults aged 2044 years
with current asthma and with skin prick test results.
Main outcome measure Severity of asthma according
to score based on forced expiratory volume in one second, number
of asthma attacks, hospital admissions for breathing problems,
and use of corticosteroids in past 12 months.
Results The frequency of sensitisation to moulds (Alternaria
alternata or Cladosporium herbarum, or both) increased significantly
with increasing asthma severity (odds ratio 2.34 (95% confidence
interval 1.56 to 3.52) for either for severe v mild
asthma). This association existed in all of the study areas (gathered
into regions), although there were differences in the frequency
of sensitisation. There was no association between asthma severity
and sensitisation to pollens or cats. Sensitisation to Dermatophagoides
pteronyssinus was also positively associated with severity.
In multivariable logistic regressions including sensitisation
to moulds, pollens, D pteronyssinus, and cats simultaneously,
the odds ratios for sensitisation to moulds were 1.48 (0.97 to
2.26) for moderate v mild asthma and 2.16 (1.37 to 3.35) for
severe v mild asthma (P < 0.001 for trend).
Conclusions Sensitisation to moulds is a powerful
risk factor for severe asthma in adults. This should be taken
into account in primary prevention, management, and patients'
education.
The severity of asthma varies widely between patients. Mild
cases are characterised by normal lung function and patients
are asymptomatic most of the time, whereas severe cases are characterised
by permanently impaired lung function and frequent exacerbations.
Little is known about the factors associated with severity, but
the identification of such factors is necessary for management
and prevention.
Sensitisation to airborne allergens might be involved in the
underlying mechanisms of severity. The associations between exposure,
sensitisation, and asthma have suggested that house dust mite,1
2 animal dander,3 4 cockroaches,5 pollens,6 and mould spores7
have a causal role in development. However, the associations
between sensitisation to different allergens and the severity
of asthma have been poorly explored.
Sensitisation to moulds has been suggested as a risk factor for
life threatening asthma. In a study of 11 patients with episodes
of respiratory arrest, 10 had positive results on skin prick
testing for Alternaria alternata compared with only
31 of the 99 matched controls with asthma and no history of respiratory
arrest.8 It was recently reported that 20 of 37 (54%) patients
admitted to an intensive care unit for asthma had a positive
result on skin testing for one or more fungal allergens (Alternaria
tenuis, Cladosporium cladosporoides, Helminthosporium maydis,
or Epicoccum nigrum) compared with 30% in patients not admitted
to intensive care units. The patients admitted to intensive care
units were no more likely than the other patients to have positive
results on skin tests for grasses, cat dander, or house dust
mites.9 Furthermore, a study of the effects of environmental
moulds during the pollen season showed that mean concentrations
of mould spores, but not of tree, grass, or ragweed pollen, were
significantly higher on the days when there were deaths related
to asthma than on the days when no such deaths occurred.10 Thus
there is evidence for an association between sensitisation and
exposure to moulds and life threatening exacerbations of asthma.
However, the hypothesis that sensitisation to moulds is generally
associated with the severity of asthma remains to be investigated.
In a preliminary study based on data from population samples
of young adults collected in two French centres we found that
sensitisation to Alternaria was associated with severity
of asthma in a population of young adults. However, few participants
had severe asthma (n=21) and there were not enough positive results
on skin prick tests to investigate the effect of other moulds.11
We used data from 1132 people with asthma from the entire dataset
of the European Community respiratory health survey to assess
whether the severity of asthma is associated with sensitisation
to airborne moulds rather than to other seasonal or perennial
allergens. Methods
The methods of the survey have been fully described elsewhere.12
13 Briefly, participating centres randomly selected samples of
20 to 44 year olds. Participants completed a short postal questionnaire
about asthma and asthmalike symptoms (stage 1). At stage
2 about 20% random subsamples of responders were invited to attend
a local test centre to complete a more detailed questionnaire
administered by an interviewer and undergo skin prick and blood
tests, assessment of lung function by spirometry, and airway
challenge with methacholine. In addition, all participants who
were not in the random subsamples but who reported in the postal
questionnaire that they had been woken up by an attack of shortness
of breath, had had at least one asthma attack in the past 12
months, or were currently taking medicine for asthma were also
invited to participate in the stage 2 (symptomatic sample). The
detailed questionnaire included questions about smoking, occupation,
social status, home environment, medication, and use of services.13
Standardised skin prick tests were carried out with allergen
coated lancets (Phazets, Pharmacia Diagnostics, Uppsala, Sweden).
The allergens selected in all centres were A alternata, Cladosporium
herbarum, Phleum pratense (timothy grass), birch, olive,
Parietaria judaica (pellitoryofthewall), common
ragweed (Ambrosia artemisifolia), Dermatophagoides
pteronyssinus (house dust mite), and cat. An uncoated lancet
was used as the negative control. Tests were performed on the
volar surface of the forearm with a standard template. Weal size
was recorded at 15 minutes as the biggest diameter and the diameter
at 90° to its midpoint, each to the nearest whole millimetre.
The mean weal diameter was calculated as the average of the two
diameters. Results were regarded as positive if the mean weal
diameter was at least 3 mm greater than that for the negative
control. Baseline forced expiratory volume in one second and
forced vital capacity were measured by standardised methods,
most often with a Biomedin spirometer (Biomedin, Padua, Italy).14
Definitions of asthma and severity
Participants were defined as currently having asthma if they
answered yes to the question"Have you ever had asthma?"and
if they had had at least one asthma attack or had taken inhaled
or oral corticosteroids for asthma in the past 12 months. Asthma
was classified as mild, moderate, or severe according to a score
derived from Ronchetti et al15 and based on the forced expiratory
volume in one second (mild > 80%, moderate 7080%, severe < 70%
predicted), the number of asthma attacks in the past 12 months
(2, 36, > 6), the number of admissions to hospital for
breathing problems in the past 12 months (0, 12, > 2),
and whether inhaled or oral corticosteroids had been taken in
the past 12 month. Each of the first three variables had three
levels of increasing severity (scored 1, 2, 3) and the fourth
variable had two levels (scored 1 or 2). The overall total score
therefore ranged from 4 to 11, with levels of severity levels
being mild (score 4 or 5), moderate (6), or severe (>7).
Analysis
We used the data from stage 2 from the 30 centres that performed
skin prick tests for the nine allergens mentioned above. The
population, response rate, and prevalence of asthma in the centres
have been reported previously.16-18 Of the 17 089 participants
examined for stage 2 in those 30 centres, complete data for all
skin prick tests were available for 14 098. Of those, 1351 currently
had asthma and in 1132 severity could be classified (missing
data: 35 for forced expiratory volume in one second, 181 for
the number of attacks, and 3 for both). The 1132 participants
included in the analysis did not differ according to age, sex,
smoking, or result to skin prick test from the 219 patients who
could not be classified. Figure 1 shows details of the study
design and the numbers of participants involved at each stage.
We used the SASPC statistical package (SAS Institute, Cary,
NC) for statistical analysis. We assessed the associations between
severity of asthma (mild, moderate, severe) and categorical variables
using X2 test and tested for trend with MantelHaenszel
tests. We gathered data from the 30 centres within regions: United
Kingdom and Republic of Ireland), northern Europe (Iceland, Norway,
Sweden), central Europe (Belgium, France, the Netherlands), southern
Europe (Italy and Spain), Australia and New Zealand, and United
States (Portland was the only area in the United States). As
we found no heterogeneity between regions in the association
between severity and sensitisation to allergens (P > 0.30
for all allergens except D pteronyssinus, for which
P=0.13) we performed logistic regressions to estimate adjusted
odds ratios for the associations between severity and sensitisation,
taking potential confounding factors into account and with regions
included in the model as an additional explanatory variable.
We used nominal logistic regressions to assess odds ratios for
moderate versus mild
Fig 1 Study design and patients involved at each stage for 30 centres included in present analysis |
Results
Of the 1132 people with asthma in this study, 564 (50%) had mild
asthma, 333 (29%) had moderate asthma, and 235 (21%) had severe
asthma. Severity was not related to age, sex, smoking, passive
smoking, or parental history of asthma (table 1). Table 1 also
shows the features of severity that we used to classify participants
into categories.
The proportion of people with mild asthma varied according to
geographical area, ranging from 63% in southern Europe to 42%
in Australia and New Zealand. The proportion with severe asthma
was 15% in southern Europe, 17% in central Europe, 17% in northern
Europe, 21% in the United Kingdom and Republic of Ireland, 28%
in Australia and New Zealand, and 26% in Portland.
Over 73% of participants were sensitised to at least one allergen
and 65% were sensitised to two or more. Sensitisation to moulds
alone was extremely rare: nine people were sensitised to Alternaria only
and two to Cladosporium only. The proportion of people
with asthma with sensitisation to the various allergens varied
according to the regions (table 2). Sensitisation to moulds was
the lowest in southern Europe and the highest in Portland and
in the United Kingdom and Republic of Ireland.
Table 3 shows that sensitisation to moulds was significantly
associated with severity of asthma. For both Alternaria and Cladosporium the
proportion of sensitised people increased with increasing severity
(P < 0.001 for trend). For Alternaria the odds ratio
was 1.64 for moderate versus mild asthma and 2.05 for severe
versus mild asthma. These remained unchanged in the multivariable
models after we adjusted for possible confounding factors. For Cladosporium the
odds ratio was > 3 for severe versus mild asthma. When we
considered sensitisation to either mould, the odds ratio was
2.34 for severe versus mild asthma (P < 0.001).We observed
similar patterns for the association between sensitisation to
moulds and severity of asthma (severe versus mild asthma) in
all regions (fig 2).
Table 1 Characteristics of study population. Figures are numbers (percentage) of participants unless stated otherwise |
Table 2 Proportions (%) of participants
with asthma with sensitisation to allergens tested
in six regions of European Community respiratory health
survey (ECRHS) |
Table 3 Associations between sensitisation to moulds and severity of asthma (% of sensitised participants by severity and odds ratios (95% confidence interval) for moderate versus mild asthma and severe versus mild asthma) |
Table 4 Associations between sensitisation to pollens and severity of asthma (% of sensitised participants by severity and odds ratios (95% confidence interval) for moderate versus mild asthma and severe versus mild asthma) |
The results were virtually identical when we included the number
of allergens the participants were sensitised to in the models.
Discussion
Our study of asthma from large population based samples of adults
living in different countries showed that the severity of asthma
is associated with sensitisation to Alternaria and Cladosporium but
not to pollens.
Fig 2 Multivariable adjusted odds ratios (95% confidence interval) for association of severe versus mild asthma with sensitisation to moulds (either Alternaria alternata or Cladosporium herbarum, or both) by region (adjusted within region for age, sex, smoking habits, passive smoking, and parental history of asthma) with combined odds ratio from model with region included as random effect |
Table 5 Associations between sensitisation to Dermatophagoides pteronyssinus or to cats and severity of asthma (% of sensitised participants according to severity and odds ratios (95% confidence interval) for moderate versus mild asthma and severe versus mild asthma) |
Table 6 Associations between severity of asthma and sensitisation to moulds (Alternaria alternata or Cladosporium herbarum), pollens, Dermatophagoides pteronyssinus, and cats. Multivariate adjusted* odds ratio (95% confidence interval) for moderate versus mild asthma and for severe versus mild asthma |
the data after excluding the 110 patients taking oral corticosteroids.
The multivariate adjusted odds ratios for the association between
moulds (either Alternaria or Cladosporium) and severity
were 1.65 (95% confidence interval 1.08 to 2.50) for moderate
versus mild asthma and 2.49 (1.55 to 3.99) for severe versus
mild asthma. These results are similar to those presented in
table 3.
We considered hospital admissions in the past 12 months in the
classification of asthma severity, but in only a few participants
(2.2%) was this relevant. Our results do not therefore duplicate
those of previous studies of life threatening asthma.
To date, there has been little evidence that sensitisation to
moulds is associated with severity of asthma. A study of 343
children aged 7 to 12 years recruited from a paediatric practice
investigated the association between sensitisation to individual
allergens and the frequency of episodes of wheezing. The proportion
of children sensitised to A tenuis increased with the
number of episodes. However, significant associations were also
observed for sensitisation to mites and especially to cats.25
The relation between skin test reactivity and forced expiratory
volume in one second was examined in children aged 6 to 12 years
with asthma or frequent wheezing as part of the second national
health and nutrition survey. Low forced expiratory volume in
one second was associated with reactions to house dust, Alternaria,
dogs, ragweed, oak, and Bermuda grass allergens.26
To our knowledge no population studies apart from the European
Community respiratory health survey have investigated the association
between severity of asthma and sensitisation to allergens in
adults. In a study of the relative importance of sensitisation
to individual allergens for bronchial hyperresponsiveness in
the United Kingdom within the framework of the European survey,
people with positive results to Cladosporium were considerably
more responsive than those with positive results to cats or timothy
grass.27 Analysis of Spanish data showed that sensitisation to Alternaria,
cats, and timothy grass was associated with a decrease in forced
expiratory volume in one second in women.28 In a preliminary
study based on data from two French centres we found that sensitisation
to Alternaria was associated with severity of asthma.11
As the importance of sensitisation to moulds as a risk factor
for severe asthma may be dependent on area, the European survey
was an unique opportunity to assess the consistency of the association.
Data were collected with thoroughly standardised methods in comparable
populations. Consistency of results across the survey areas has
not always been observed for other issues. For example, the association
between symptoms of asthma and lung function and the use of gas
appliances varied considerably between areas.29 30 In contrast,
the association between severity and sensitisation to moulds
was remarkably consistent, though there were differences in the
distribution of severity and in the frequency of sensitisation
to the various allergens in the various areas, despite the fact
the gathering of centres into regions is necessarily arbitrary.
We observed a differential association between moulds and pollens
and severity of asthma. Possibly the size of fungal spores allows
them to reach the lower airways and also they may be inhaled
by means of fragments and other amorphous bioaerosols. Pollens
are larger and their effect on asthma requires exceptional situations
such as thunderstorms, when pollen is concentrated by changes
in air flow, grains are ruptured by osmotic shock, and each grain
releases hundreds of starch granules that are small enough to
be respired.31 Other explanations for the different
| What is already known on this topic |
Sensitisation to moulds is a known
risk factor for life threatening exacerbations of asthma |
| What this study adds |
The prevalence of sensitisation
to moulds (Alternaria alternata or Cladosporium
herbarum, or both) increased with increasing severity
of asthma |
Contributions: All authors conceived and initiated this study
within the framework of the European Community respiratory health
survey. MZ designed and performed the analysis, wrote the first
draft of the paper, and is guarantor. CN helped with analysis,
interpretation, and writing the paper. BL conducted part of the
statistical analysis and helped in interpretation. RL gave substantial
help to writing the paper. JB participated in study design and
interpretation. FN was principal investigator and participated
in study design, analysis, and interpretation. MZ and CN participated
in the data collection for the Paris centre.
Funding: Australia: Allen & Hanbury, Australia;
Belgium: Belgian Science Policy Office, National Fund for Scientific
Research; France: MinistËre de la SantÈ, Glaxo France,
Institut Pneumologique d'Aquitaine, Contrat de Plan EtatRÈgion
LanguedocRoussillon, CNMATS, CNMRT (90MR/10, 91AF/ 6), Ministre
dÈlÈguÈ de la santÈ, RNSP, MinistËre
de l'Environnement (No 96115EN96D4); Germany: GSF, Bundesminister
f¸r Forschung und Technologie, Bonn; Greece: Greek Secretary
General of Research and Technology, Fisons, Astra, BoehringerIngelheim;
India: Bombay Hospital Trust; Italy: Ministero dell'Univesit‡ e
della Ricerca Scientifica e Tecnologica, CNR, Regione Veneto
Grant RSF No 381/05.93; New Zealand: Asthma Foundation of New
Zealand, Lotteries Grant Board, Health Research Council of New
Zealand; Norway: Norwegian Research Council project No 101422/310;
Portugal: Glaxo FarmacÍutica Lda, Sandoz Portugesa; Spain:
Ministero Sanidad y Consumo FIS (grants 91/0016060/OOE05E,
92/0319, 93/0393), Hospital General de Albacete, Hospital General
Juan RamÛn JimÈnenz, Consejeria de Sanidad Principado
de Asturias; Sweden: Swedish Medical Research Council, Swedish
Heart Lung Foundation, Swedish Association against Asthma and
Allergy, Swedish Society of Medicine, Astra, GlaxoWellcome,
BoehringerIngelheim; Switzerland: Swiss National Science
Foundation Grant 402628099; United Kingdom: National Asthma
Campaign, British Lung Foundation, Department of Health, South
Thames Regional Health Authority; United States: US Department
of Health, Education and Welfare Public Health Service Grant
No 2 S07 RR0552128.
Competing interests: None declared.
Skin
prick testing is conventionally used to investigate immediate
type hypersensitivity to allergens in patients with rhinoconjunctivitis,
contact urticaria, asthma, atopic eczema, and suspected food
allergy. It is also a means of detecting allergen specific IgE
and has the advantage of being relatively inexpensive, providing
immediate results compared with measurement of serum allergen
specific IgE by radioallergosorbent testing (RAST).
The technique used for skin prick testing involves puncturing
the skin with a calibrated lancet (1 mm) held vertically, or
a hypodermic needle or blood lancet at an angle of 45°, and
introducing a drop of diluted allergen. All patients undergoing
skin prick testing should also have a positive histamine control
and negative diluent (saline) control test included. An itchy
weal should develop at the histamine puncture site within 10
minutes. Test solutions are standardised to give a mean weal
diameter of 6 mm. The maximum or mean diameter of the weals to
various allergens should be read at 15 minutes. A weal of 3 mm
or more in diameter is generally considered to represent a positive
response (indicating sensitisation to the allergen). The negative
control is important because it excludes the presence of dermographism,
which if present makes the tests difficult to interpret.
The relevance of skin prick testing should be interpreted in
the context of the patient's history. Positive results can occur
in people without symptoms and, similarly, false negative results
may occur. "Blanket" allergy testing (whether by
skin prick testing or serological methods) can give false positive
results and, particularly in the case of foods can lead to unnecessary
dietary restrictions. Standardised solutions to a wide range
of allergens are available commercially. For more labile allergens
(such as those found in fruit and vegetables) fresh produce should
be used. Skin prick tests to aeroallergens are generally considered
safe, but intramuscular adrenaline should be available and full
resuscitation facilities are needed when test are carried out
with other allergens such as foods and natural rubber latex.