Recently, a rise in the percent of children suffering from various respiratory disorders has been observed.1
It has been observed that respiratory allergic patients suffer from acute asthmatic attacks more frequently during the changing season and weather conditions.21
Fungi are potent aeroallergens and atmospheric surveys have reported that seasonal variations in fungal concentrations could be the prime cause of clinical allergy and asthma.8
Previous studies at various places in India including Delhi have focused only on occupational environments; therefore, the present aerobiological study is the first to be performed in Delhi (India), emphasizing on qualitative and quantitative prevalence of the clinically significant aerospora inside and outside the homes.
The studies performed in different countries provide variable results of total fungal concentration and distribution of fungi because it basically depends on media and sampling method used, season of the year, geographical location, and living conditions as well as fungal growth substrates in different countries.22
We have collected 1-year quantitative data on tropical fungi from each home and fungal concentrations were high when compared with other studies.8,23–25
Shelton et al.26
recorded the medium concentration of 500 CFU/m3
in the United States. Takahashi27
observed a concentration range of 13–2750 CFU/m3
from the city of Yokohama, Japan. de Ana et al.28
isolated a total of 11,843 fungal colonies per cubic meter ranging from 0 to 1666 CFU/m3
in different homes of allergic patients from Barcelona, Spain. The higher concentration could be caused by tropical vegetation in and around Delhi and conducive temperature and humidity.
Among the 35 fungal genera isolated, the prevalent fungal groups from all of the homes were different species of Aspergillus
, and Cladosporium.
Nonsporing isolates and yeast were also frequently isolated but they were grouped into “others.” Some of these fungi have been reported as the most common airborne fungi in different environments in other studies also12,23,26–30
and have been considered to be the potent allergens in aerospora of many indoor and outdoor environments contributing to the increase in respiratory diseases in children as well as adults.31–33
was the most diverse genera in terms of number of species identified in the present study. A. niger
, A. flavus
, A. fumigatus
, A. versicolor
, A. nidulans
, and Aspergillus variecolor
were more common than other species. Aspergillus
was also the most dominant fungal group in the present study. A similar result was also found by Singh et al.29
and Pandit et al.12
in Delhi, India. Khan et al.
from Kuwait have also found Aspergillus
species to be the predominant component of the aerospora. Fungal genera other than four fungi were Fusarium
, and Rhizopus.
genera, Penicillium citrinum
, Penicillium chrysogenum
, Penicillium oxalicum
, and Penicillium nigricans
were the most frequent species.
We scored significant seasonal variations in indoor as well as outdoor culturable airborne fungi. Aspergillus
are more prevalent in autumn and winter, whereas Cladosporium
was more prevalent in winter and summer. Such seasonal distributions have also been reported in the homes of United States10,25
In the United States,25
an unexpectedly high fungal spore concentration has been observed during winter. Alternaria
is most predominant in dry weather (summer), as observed by other workers in other parts of the world.28,34
In occupational environments such as the bakery and sugar industry, definite sources of fungal growth are present, even then seasonal patterns in fungal concentration have been reported,13,35
which indicates that patients are definitely exposed to fungi according to their seasonality. Therefore, it becomes important to include seasonal variations in fungi in any study model because the concentration of any fungi taken at one time can not be representative of the level throughout the year.9
Different species of Aspergillus
had marked seasonality, but variations are observed in particular seasonal predominance. For example, A. fumigatus
and A. nidulans
, being xerophilic fungi, are prevalent in summer, whereas, A. flavus
and A. niger
are predominant in autumn. These variations are in conformity with studies performed elsewhere.27,36–38
The highest concentration of Alternaria
is 137 CFU/m3
inside the homes and 169 CFU/m3
immediately outside the homes in the month of April (summer; the values are calculated for CFU/m3
per sampling). Both of these values exceed 100 CFU/m3
, which have been related to hyperresponsiveness of airways in children sensitive to Alternaria
, the allergens of which contribute to severe asthma in regions where exposure to the fungus is high.39
According to the Wilcoxon signed-rank test, the indoor and outdoor CFU levels integrated over the entire test period are not significantly different, although indoor presence of fungi is slightly higher, but overall, no statistical difference was observed between indoor and outdoor fungal levels, except for Aspergillus
spp., which is considered primarily to be an indoor allergen.40
It has been proposed that indoor air spora is representative of that present in the outdoor environment as in present study airborne fungi observed indoors paralleled with those outdoors, although quantitative variations may exist that may be caused by the presence of indoor fungal source, dampness in home, or use of air conditioners and humidifiers, etc.
In India, and especially in middle class families, use of air conditioners and humidifiers is not very common. Similar results have also been seen in the homes of mold-sensitive children with asthma in a U.S. city6
and in Taiwanese school children,41
where the concentration of airborne fungi encountered indoors generally paralleled with those found outdoors as observed in the present study.
We observed higher levels of fungal concentration in the homes of patients when compared with that in control (nonallergic) homes in indoor air. However, except in a few cases (Mucor spp., Rhizopus spp., and Curvularia spp), statistical difference in their concentration is found lacking. The lack of quantitative difference in airborne fungi between patients and control homes could be because of the fact that genetically predisposed children are more likely to suffer from respiratory trouble.
All of the fungi occurred (percent occurrence) at significantly higher rates inside the homes when compared with immediately outside the homes. It was also observed that significantly higher rates of percent occurrence of the dominant fungi was present in the homes of patients when compared with that in nonasthmatic/healthy volunteer homes, which is in contrast to mold concentration where statistical significance was not observed. It is a common observation that once the air infiltrates inside the home, the spores do not find an escape route to the outside air. These spores get settled in the dust and become airborne whenever there is any human disturbance. Regular removal of dust by vacuuming or wiping also removes the infiltrated spores, but lack of such activities might be responsible for longer persistence of spores inside the patients' homes. The level of fungal spores inside the homes has been analyzed in New York, and it is found that characteristic of housing (habitat) might predict higher or lower concentrations of spores in the dust.42
The I/O ratio is another indicator for evaluating the difference between indoor and outdoor fungal levels as well as house-to-house variation of dominant fungi because indoor and outdoor distribution of fungi was not similar in all of the homes as evident from the CoVs observed. Most of the dominant genera have few homes with I/O ratio >2 excluding Aspergillus (18–26%), Penicillium (13%), Curvularia (18.2%), and Rhizopus (14.3%). Some of the dominant genera are also observed to be absent in immediate outdoors. For example Mucor is not recovered from immediate outdoors from 32 homes, indicating its immediate source inside the homes.
Li et al.
have examined the homes of 46 asthmatic children and observed that Aspergillus
are more prevalent indoors when compared with outdoors with I/O ratios >2.41–43
Asthmatic children living in such houses have been studied in detail in the United States for their respiratory dysfunction and sensitivity to these fungi (unpublished data). Earlier work from our laboratory has established the role of Aspergillus
and other fungi in patients of different occupational settings.44,45
Important pollen and fungal aeroallergens from India have recently been reviewed by Singh and Shipra.46
There is similarity in the fungal composition in different environmental studies, but there are great variations of the concentration as well as percent contributions of fungi. This indicates that the concentration percentages of fungal groups are influenced by the sampling methodology and environmental conditions.47
There can be plausible correlation between the seasonal changes in the symptoms of asthma and fungal spore counts because marked seasonal fluctuations are observed in various fungi as shown by the studies in other countries.7,48,49
Prevalence of sensitization is also essential to evaluate the effect of exposure, which will be included in additional publications. It is important to be aware of the fungal flora in places where asthmatic people reside for proper diagnosis and management of the disease and, therefore, proper investigations and valid approaches are of immense clinical importance to evaluate the relationships between the health symptoms and microfungal concentration.