Discussion
During the COVID-19 pandemic, the NPI have profoundly impacted allergen
sensitization. This study reached the following conclusions by analyzing
the results of inhaled allergen sIgE testing in 29,926 cases before and
during the COVID-19 pandemic: (1) During the pandemic, the positive rate
of indoor and outdoor allergens increased significantly, and the outcome
remained the same after adjusting potential influencing factors such as
gender, season, and age. (2) Dust mite allergen sIgE grade and multiple
sensitization rate have increased during the COVID-19 pandemic. (3) The
allergens sensitization differed by gender, age, and season.
The risk of indoor allergen sensitization during the COVID-19 is 1.2 to
4 times higher than that before the COVID-19 (OR
range:1.194~4.014, P<0.05) . Li
Y[8] discovered that the positive rate of indoor
allergens in South China increased dramatically during COVID-19
pandemic. The study of Qing Ye[9] also observed
that the positive rate of allergens during COVID-19 was 51.50%, higher
than 42.23% before COVID-19. Additionally, another study of Qing
Ye[10] discovered that the positive rate of indoor
allergens increased during COVID-19, while the number of positive
allergens decreased. But in our study, the number of allergens also
increased remarkably during COVID-19. The following factors may be
studied to determine the reason for increased positive rate of indoor
allergens: (1) NPI during the COVID-19 pandemic increased population
density, indoor temperature and humidity[11], as
well as the time that pets spent indoors[12],
causing the growth of indoor allergen
concentrations[9]. Wahn[13]found a dose-response relationship between inhaled allergen exposure and
allergen sensitization. Another study[14]indicated that 2ug/g of dust mites in the air was a risk factor for
sensitization, whereas 10ug/g was a risk factor for asthma among dust
mite-sensitized persons. (2) The increasing concentration of other
allergens in the air, such as mold and animal fur, will also increase
the risk of dust mite allergens sensitization, because of the
cross-reaction[15]. (3) During the COVID-19
pandemic, children spend more time indoors, which increases their
chances of being exposed to indoor allergens[16].
Repeated exposure is easy to cause allergens sensitization. It is
recommended that individuals use dehumidifiers, vacuuming, air
purification, acaricides, and open windows frequently for ventilation to
reduce indoor temperature and humidity. Additionally, allergen-reducing
measures, including removing carpets and fabric curtains, washing and
replacing mattresses and pillows, cleaning air conditioner should be
adopted to reduce the accumulation of indoor
allergens[17].
Though wearing disposable medical masks for a longer period during the
pandemic can prevent the inhalation of allergens theoretically, this
study revealed that the positive rate of outdoor allergens actually
increased during the pandemic (P <0.05). The result
contradicts the study of Qing Ye [10]. There are
five factors contributing to the increase in outdoor allergen
sensitization rate during the pandemic. Firstly, the masks currently
used on children are merely scaled-down copies of masks created for
adults which have not been specifically tested or
approved[18]. A research on FFP masks proved that
wearing a mask could not completely prevent allergen inhalation due to
facial leakage penetration and increased total inward leakage caused by
higher breathing frequencies[19]. Second, several
studies have demonstrated that long-term mask use without change
increases the chance of severe skin reactions[20],
and the impaired skin barrier provides a pathway for allergen
sensitization[21]. Moreover, outdoor activity and
allergen exposure increased with the gradual resumption of work and
school in the second half of 2020, which is proved by a significant rise
in the positive rate of w6 from June to September during COVID-19 in
this study, Furthermore, as children usually feel hot and have breathing
difficulties while wearing masks, some of them may remove the masks
during physical activities[22], raising the
prevalence of outdoor allergens during the pandemic. To decrease
allergen stimulation and allergy symptoms, it is recommended that
children reduce outside activities and use adequate masks with timely
replacement during the pollen season.
During the COVID-19 pandemic, the proportion of medium and high-level
sIgE to dust mite allergens increased, whereas the proportion of middle
and high-level sIgE to mold and cockroach allergens dropped
(P<0.05). In the same study, Qing Ye[9]discovered that, except for dust mite allergens, the majority of
allergen-specific IgE levels were lower than those before the pandemic.
This may also contribute to increased exposure to dust mite allergens by
longer time indoors during the pandemic[16].
Moreover, the proportion of multiple sensitivities grew greatly during
COVID-19 compared to that before the same period
(P<0.05) . Studies have pointed out that dust mite
sensitization is often associated with other allergens due to
antigen-cross and co-sensitivity across
allergens[23]. Therefore, when advising patients
to avoid allergens, doctors should not only focusing on the target
allergen while ignoring other frequent allergens. Studies have shown
that avoiding a single allergen cannot prevent allergy sensitization,
whereas reducing the levels of numerous inhaled allergens together can
achieve this purpose[24].
There were gender differences in the positive rate of allergens, which
has been reported in other pieces of
literature[25], yet the reason and mechanism
remain unknown. It could be the different living habits between men and
women, which may result in varied allergen
exposure[25], or the difference in hormone
secretion between the two genders[26].
The positive rate of inhaled allergens changes with age. The positive
rates of dust mites and cockroaches increased with age, as found in the
studies of Ying[25], and
D’Souza[27]. The differences in allergen
sensitization at different ages, due to the different range of activity
at different ages, might result in differences in allergen exposure.
Clinicians should give recommendations to patients properly in avoiding
allergen sensitization based on the distribution characteristics of
allergens in different age groups and the trend of allergen
sensitization with age.
This study also discovered that the positive rate of inhaled allergens
was higher in summer and autumn than in winter and spring, and similar
conclusions were found in an analysis of allergen sensitization in
children in Shanghai, China[25]. This is due to
seasonal differences in allergen concentrations in the air caused by the
characteristics of various allergens. Dust mite reproduction peaked in
July and August and began to decline in October[28]. Animal hair sheds primarily in the summer
and autumn. Trees bloom in the spring, grasses in the late spring to
early summer, and weeds in the autumn [29]. As a
result, patients who are sensitive to inhalation allergens should wear
masks based on the seasonal distribution characteristics of local
allergens to avoid contact with allergens and reduce allergen
stimulation and allergic reactions.
There are currently few studies investigating the impact of the COVID-19
pandemic on allergen distributions. This study offers nearly 30,000 test
results from large sample size and includes an analysis of indoor and
outdoor allergens, which can be used as a reference for the prevention
and control of allergens sensitization under normal pandemic conditions.
Nevertheless, this study has some limitations. It lacks data on allergy
diseases in the study population for the privacy of the study
population, making it impossible to assess the association between the
COVID-19 pandemic and allergic diseases. Future studies can therefore
investigate whether the COVID-19 pandemic influences the prevalence of
allergy diseases.