• cat allergens;
  • dwelling characteristics;
  • East–West German comparison;
  • house-dust-mite allergens;
  • indoor allergen exposure


  1. Top of page
  2. Abstract
  3. Material and methods
  4. Results
  5. Discussion
  6. Acknowledgment
  7. References

The background of this study is the finding of several studies that the frequency of respiratory allergies was significantly higher in the former West Germany than the former East Germany. The present study investigated the levels of allergens of house-dust mite (Der p 1 and Der f 1), cat (Fel d 1), and cockroach (Bla g 2) in the household dust of 201 homes in Hamburg (West Germany) and 204 homes in Erfurt (East Germany), and examined the factors that affect these levels. The characteristics of homes were assessed by a questionnaire. The allergen levels were studied in dust from living rooms (LR), bedrooms (BR), and mattresses (MA). We detected in samples from Hamburg significantly higher allergen concentrations than in Erfurt: three times higher Der p 1, five times higher Der f 1, and three times higher Fel d 1. For Bla g 2, no comparison was possible because the concentrations were below the detection limit in 93% of the samples. Most of the differences could be explained by differences in housing and living characteristics between both cities. The mean ratio of Der p 1 levels in mattress dust between Hamburg and Erfurt decreased from 4.1 to 1.54 (NS) after adjustment for season, building material, age of the house, story of the dwelling, type of heating, age of carpet/mattress, presence of dogs, and indoor climate (temperature, humidity). The mean ratio of Der f 1 levels decreased from 6.9 to 2.78 (P<0.05) after adjustment for these factors. The mean ratio for Fel d 1 in mattress dust decreased fom 4.03 to 1.65 (P<0.05) after adjustment for season, building material, story of dwelling, size of dwelling, ventilation, cleaning routines, and pets. A similar reduction was seen for floor dust (LR plus BR). Our results indicate that the differences between the concentrations of mite and cat allergens found in Hamburg and Erfurt are explicable mainly, but not completely, by different building characteristics (age of houses, building material, story, and size of the dwelling) which affected the indoor climate, as well as by differences in other individual living habits (keeping of pets, age of carpets or mattresses, and cleaning routines).

In recent years, a continuous increase in IgE-mediated atopic disorders such as hay fever and asthma has been observed worldwide ( 1). The causes of this increase seem to be multifactorial in that genetic and environmental factors work together.

The reunification of Germany offered a unique opportunity to compare the prevalence of atopic diseases between the East and West German populations ( 2–7). All these studies yielded some unexpected results. Although there were much higher levels of ambient sulfur dioxide and total suspended particulates in East Germany, the frequencies of respiratory allergies and specific IgE levels were significantly higher in subjects from West German regions. The reasons for the lower prevalence of atopic sensitization in East Germany are still unknown. The genetic background in both parts is probably similar, and several suggestions regarding different living conditions over the last 40 years are rather speculative ( 8). Many East Germans live in multifamily concrete slab or brick houses in rather small and crowded apartments. Furthermore, the former East German homes were poorly insulated; often the heating could not be controlled in individual apartments; because heating costs were low, occupants controlled the temperature of their apartments by opening windows ( 8). In contrast, in West German homes, high energy costs caused home owners to insulate and seal buildings. Well-insulated, airtight homes are believed to create damp environments that augment the growth of molds, mildews, and mites ( 9).

Recently, Nowak et al. ( 10) observed a higher prevalence of atopic sensitization in Hamburg (West Germany) than in Erfurt (East Germany) and suggested that childhood factors and exposure to indoor allergens and irritants were probably responsible for the differences observed between the two cities. On the basis of these observations, a joint project has been established to investigate the influences of indoor factors and genetics in asthma (INGA) ( 11).

The purpose of this study, as part of the INGA project, was to analyze the concentration of indoor allergens (house-dust mites, cat, and cockroach) in dust from randomly selected homes in Hamburg and Erfurt, respectively. We report on the influence of home conditions on allergen levels in these homes.

Material and methods

  1. Top of page
  2. Abstract
  3. Material and methods
  4. Results
  5. Discussion
  6. Acknowledgment
  7. References

Homes and dwelling characteristics

From June 1995 to November 1996, 1175 dust samples were collected from 405 homes (Erfurt, n=204; Hamburg, n=201). These homes were selected from two population samples participating in the study on the prevalence of atopic sensitization in West and East Germany ( 10).

Interviewers collected information on housing conditions and living habits, and sampled reservoir dust. A questionnaire based on that of the EC Respiratory Health Survey study ( 12) was used to obtain detailed information on type and age of the home, story, size of the dwelling, type of heating, age of carpets and mattresses, pets, signs of dampness, tightness of the windows, ventilation, and cleaning habits in the home. Indoor climate (temperature and relative humidity) was measured for a period of 7 days after dust sampling.

Dust collection and processing

In each house, three dust samples from the living room (LR) floor and the bedroom (BR) floor and mattresses (MA) were collected from 1 m2 in a standardized manner ( 13). The allergens were extracted from the sample dust plus filter paper with 0.125 M NH4HCO3 plus 0.05% Tween 20 (v/v) for 2 h at room temperature under constant shaking, with an extraction ratio of 1:10–1:100 (w/v), depending on the amount of sampled dust. The solution was clarified by centrifugation at 1000 g. The extracts were stored frozen at −20°C in separate aliquots until analyzed to avoid repeated freezing and thawing.

The allergen levels of Der p 1, Der f 1, Fel d 1, and Bla g 2 were assayed as described previously ( 13) by means of monoclonal antibodies and reference samples from Indoor Biotechnologies (Deeside, Clwyd, UK). The interassay variation for repeated assays was 10–16%, and the intra-assay variation was approximately 3.5–8%. The lower detection limits were 1 ng/ml for Der p 1 and Der f 1, 1.5 ng/ml for Fel d 1, and 0.04 U/ml for Bla g 2.

Because there is considerable potential variability in the sampling and assay of allergens ( 14), the questionnaires and dust sampling were carried out by the same fieldworkers throughout our study, and the dust samples were processed by the same technician.

Statistical analysis

The allergen levels were transformed into logarithms and analyzed with SPSS (Version 6.12). The Mann–Whitney test was used to test the level of significance of differences between variables. The Spearman rank-order correlation was used to test possible association between variables. The limit of significance chosen was 0.05. The bivariate and multivariate analyses were performed with SAS (Version 6.08, Cary, NC, USA) by linear regression of the transformed allergen levels ( 15). The mean ratio of allergen concentrations was calculated by the ratio of adjusted geometric mean versus reference category.


  1. Top of page
  2. Abstract
  3. Material and methods
  4. Results
  5. Discussion
  6. Acknowledgment
  7. References

Content of allergens in dust samples

Dust sample weights varied widely from 0.019 to 11.95 g. Likewise, the physical appearance of the samples varied greatly, ranging from small amounts of fine dust to large quantities of hair, fuzz, and debris. Therefore, we analyzed the allergen content as concentration per unit weight and per area sampled. Highly statistically significant correlations were found between the amounts of all four allergens expressed as μg/g unsieved dust and those expressed as μg/m2, ranging from 0.92 to 0.99.

Mite allergens (Der p 1 or Der f 1) were detected in 78%, Fel d 1 in 89.5%, and Bla g 2 in 7.1% of the samples analyzed (n=1175). We were unable to detect any of the allergens mentioned in only two (Erfurt) of 405 houses. By the proposed provisional guidelines on threshold levels, 52% of homes had at least one site with total levels of mite allergen (Der p 1 or Der f 1) over 2 μg/g, and 20.5% of homes had at least one site with Fel d 1 levels over the significant range (≥8 μg/g).

The distribution of allergens between Hamburg (n=578) and Erfurt (n=597) is summarized in Table 1. Although the collected dust amounts were not significantly different between the two cities, the allergen levels for Der p 1, Der f 1, and Fel d 1 were generally lower in Erfurt than in Hamburg. We detected in Hamburg three times higher Der p 1 levels and even five times higher Der f 1 levels. The Fel d 1 concentrations in dust from Hamburg were three times higher than in dust from homes in Erfurt. The number of Bla g 2-positive samples was too low for further statistical analysis.

Table 1.  Statistical characteristics of allergen levels in dust samples from Hamburg (West Germany) and Erfurt (East Germany)
 Der p 1 (μg/g dust) Der f 1 (μg/g dust) Fel d 1 (μg/g dust) Bla g 2 (U/g dust)
  1. LR: living room; BR: bedroom; MA: mattress.

Dust samples (LR+BR+MA)
Geometric mean0.0360.1110.0870.4140.2730.879<0.4<0.4
25th percentile<0.01<0.01<0.01620.0540.118<0.4<0.4
75th percentile0.17710.6672.9990.5355.780<0.4<0.4
Floor dust (LR+BR)
Geometric mean0.0240.0640.0620.2520.3140.897
Mattress dust
Geometric mean0.0840.3440.1611.1140.2120.853

The proportion of Der f 1 over Der p 1 was also different in both cities. Geometric mean values in Hamburg were 0.414 and 0.111 μg/g dust for Der f 1 and Der p 1 (ratio: 3.7), respectively. The corresponding values in Erfurt were 0.087 and 0.036 μg/g dust (ratio: 2.4), respectively.

Furthermore, the frequency and the content of the three allergens in the different sampling locations were analyzed between the two cities ( Table 1). As expected, the Der p 1 and Der f 1 concentrations in mattresses were higher than those of the floors of bedrooms and living rooms. In contrast, the concentrations of Fel d 1 allergen were higher in living room dust than in dust collected from bedrooms or mattresses, but only within samples from Erfurt. The Fel d 1 content of homes in Hamburg did not show statistically significant differences in the sampling locations. In general, we detected in all sampling locations in Hamburg significantly higher concentrations of Der p 1, Der f 1, and Fel d 1.

Association between allergen content and dwelling characteristics

Since the homes in Erfurt and Hamburg had different distributions of allergen levels, different housing factors were evaluated with regard to important factors associated with the presence of mite ( 15) or cat allergen ( 17) ( Table 2).

Table 2.  Building characteristics of homes and individual occupant conditions in Erfurt (n=204) and Hamburg (n=201)
CharacteristicsP value*Erfurt (East Germany) nHamburg (West Germany) n
  1. *Differences between two cities were tested by chi-square test. NS: not significant; LR: living room.

Age of home<0.001
 Before 1945  77 70
 1946–70  23 84
 After 1970 104 47
Building material<0.001
 Brick houses  88135
 Concrete slab houses  93 10
 Concrete houses   7 49
 Framework/clay houses  12  3
Story of dwelling<0.001
 Ground floor  59 87
 1st floor  31 46
 2rd/3th floor  64 46
 4th floor and higher  50 22
Size of dwelling<0.001
 ≤50 m2  29 20
 >50–≤100 m2 146123
 >100 m2  29 58
Type of heating 0.0574
 Central 144124
 Not central  59 76
Median of relative humidity (LR)  0.004
 ≤45%  99 85
 >45–≤60%  67 87
 >60%   6 21
Median of temperature (LR)  0.001
 ≤20°C  35 41
 >20≤23°C  93121
 >23°C  58 29
Tightness of windows (LR)<0.001
 Good  98159
 Bad  68 37
Age of carpet in LR<0.001
 ≤1 years  48 24
 2–4 years  66 35
 5–9 years  53 67
 ≥10 years  30 59
Age of mattress  0.0339
 ≤1 years  40 29
 2–4 years  69 56
 5–9 years  40 64
 ≥10 years  51 49
Pets in home during last year
  Yes  17 46
  No 187155
 Dog  0.0286
  Yes  39 57
  No 164143

In Hamburg, 77% (49% in Erfurt) of the subjects live in houses more than 25 years old, and 93% (47.5% in Erfurt) of the houses are made from bricks or from concrete. More of the dwellings were on the ground floor or the first floor (66% in Hamburg, in contrast to 44% in Erfurt); consequently, these characteristics could influence the indoor climate (temperature, relative humidity, and signs of dampness). Although no significant differences (P=0.057) were present in the heating systems either in Hamburg or in Erfurt, significant differences were found with respect to the indoor climate. Homes in Hamburg were damper than those of Erfurt. The greater tightness of the windows of houses in Hamburg has to be mentioned with regard to the findings (P<0.001). Likewise, potentially important specific factors, such as the age of carpets, and mattresses, were significantly different. In Erfurt homes, 58% (LR) and 64% (BR) of carpets were newer than 5 years, in contrast to Hamburg, where the figures were only 32% (LR) and 25% (BR), respectively. More people in Hamburg had cats (P<0.001) and/or dogs (P=0.02). For all appropriate characteristics, the bivariate association with the allergen concentration for Der p 1, Der f 1, and Fel d 1 was investigated on the floors and mattresses. Because many of the building and housing characteristics were found to be related, a multiple regression analysis was performed separately for each allergen, in which initially all variables were entered which had at least a marginally significant (P<0.10) relationship to the allergen concentration in the dust ( 15).

For the mite allergens Der p 1 and Der f 1, the following factors were entered into all the models in addition to the a priori variables (city and season): building material, year of construction, story of the dwelling, type of heating system, age of carpet or mattress, presence of a dog during the last 12 months, additional humidity giving a measure for dampness of the house, indoor relative humidity, and indoor temperature. The mean ratio of Der p 1 concentration in floor or mattress dust was reduced, and no significant differences between Hamburg and Erfurt were found, when adjusted for these parameters, as shown in Table 3. In contrast, the mean ratio of Der f 1 levels remained significantly associated with the place of residence even after adjustment for these potential explanatory or confounding factors.

Table 3.  Relationship between place of residence and Der p 1, Der f 1, and Fel d 1 allergens in floor and mattress dust
Place of residenceDer p 1 levelDer f 1 levelFel d 1 level
 Mean ratio95% CIMean ratio95% CIMean ratio95% CI
  1. aAfter adjustment for season, building material, age of house, story of dwelling, type of heating, age of carpet/mattress, dog, and indoor climate (temperature, relative humidity) ( 15). bAfter adjustment for season, building material, story of dwelling, size of dwelling, ventilation, cleaning routines, and pets.

Floor dust (LR+BR)
Erfurt as reference group1 1 1 
vs Hamburg (crude, n=405) 3.43(2.00; 5.86)4.72(2.81; 7.92)2.93(1.64; 5.21)
vs Hamburg (adjusted)1.33a(0.67; 2.66)2.24a(1.09; 4.63)1.32b(0.86; 2.04)
 (n=317)  (n=317)  (n=387)  
Mattress dust
Erfurt as reference group1 1 1 
vs Hamburg (crude, n=405) 4.1(2.27; 7.40)6.9(3.72; 12.82)4.03(2.23; 7.29)
vs Hamburg (adjusted)1.54a(0.71; 3.34)2.78a(1.24; 6.23) 1.65b(1.03; 2.65)
 (n=320)  (n=320)  (n=391)  

For the cat allergen Fel d 1, a multiple regression analysis was performed in which the a priori variables (city and season) and building material, story of dwelling, size of dwelling, ventilation, cleaning routines, and pets were included. The regression analyses explained 69% of the variance of Fel d 1 in carpet dust and 66% in mattress dust, respectively.

The amounts of Fel d 1 were significantly associated with the size of dwelling (higher in small homes), frequency of vacuuming (higher in case of low frequency), and the presence of a cat. After adjustment for the above mentioned factors, the Fel d 1 concentrations in floor dust were no longer significantly different between Hamburg and Erfurt. Although the mean ratio of Fel d 1 levels in mattress dust was reduced from 4.03 (crude data) to 1.65 (adjusted data), the differences remained significant for both cities ( Table 3).


  1. Top of page
  2. Abstract
  3. Material and methods
  4. Results
  5. Discussion
  6. Acknowledgment
  7. References

Many factors may contribute to bronchial hyperreactivity; however, there is evidence that, with increased exposure to house-dust allergen, the risk of sensitization and development of allergic diseases has increased ( 18). While the level of indoor allergens in West German homes has been examined for some years ( 16, 19), allergen exposure in East Germany has only recently been reported for mite allergens ( 20). Understandably, a comparison between levels of allergens of different studies is limited because the dwellings were selected by different criteria, and different sampling methods and laboratory analyses were used. No valid data for comparison of indoor allergen exposure between East and West German homes are available. To our knowledge, this study is the first direct comparison of indoor allergen levels in East and West German homes by the same methods.

Dust samples were collected for more than 1 year to minimize seasonal influences. The data presented here demonstrated a high prevalence of mite and cat allergens, but not of cockroach allergen, in the dust of the homes. Cockroaches are a common source of indoor allergen in some parts of the world, particularly in the homes of subjects of lower socioeconomic status ( 21). The significance of exposure and sensitization to cockroach allergens in Germany is still unknown. We could detect the major cockroach allergen, Bla g 2, in 57 (14%) of the homes investigated. However, the level of cockroach allergen was below the detection limit in 93% of the total samples studied. Pollart et al. ( 22) found up to 50 times more cockroach allergen in house dust from the kitchen floor than in that from the bedroom. But we detected Bla g 2 in only one dust sample from 25 kitchen floors in the pilot study ( 13).

Mite-allergen levels

Our results demonstrate that house-dust mites probably occur in most homes at any one time, but with a wide variation in both species and quantities. This is well known from previous studies performed in regions with a temperate climate ( 23). We were unable to detect mite allergens in only 38 homes (9.4%) (11 in Hamburg and 27 in Erfurt). We detected exclusively Der f 1 in 71 homes and in 25 only Der p 1.

A comparison of actual allergen levels with data from earlier studies is difficult because the sampling conditions (homes of atopic or nonatopic subjects, sampling time, sampling location, and sample handling) are different. Lau et al. ( 24) found median Der p 1 and Der f 1 concentrations in mattress dust in Berlin, West Germany, of 0.6 μg/g dust (133 atopics) and 0.4 μg/g dust (55 nonatopics, respectively). Higher Der p 1 (1.35–1.61 μg/g dust) and Der f 1 (2.48–2.93 μg/g dust) concentrations were found on the mattresses in southern Germany ( 16).

In keeping with most previous studies, the quantity of mite allergens was significantly higher on the mattresses than on the floors of bedrooms and living rooms in Hamburg and Erfurt.

An interesting finding was that D. farinae was the major mite species in both cities. Other investigators reported similar findings ( 16, 25, 26). Because D. farinae appears to be less sensitive to humidity loss ( 27), we suppose that the prevalence could be related to long periods of dry weather. The fact that the ratio of Der f 1 to Der p 1 was higher in Hamburg than Erfurt is difficult to explain. A possible influencing factor might be that Hamburg is an important transportation center, and it is not known how long D. farinae can survive in a semiarid environment when imported from mite-prevalent areas. Moyer & Nelson ( 28) examined dust samples from imported furniture and noted the presence of living mites after 2 years. Furthermore, another East German study showed the preponderance of D. farinae in urban homes and D. pteronyssinus in rural homes ( 20).

As stated in the literature, the number of mites in homes is related to humidity, building characteristics, and indoor lifestyle factors ( 29). In our study, a significant association of humidity (relative as well as absolute humidity), temperature, type of heating, story of the dwelling, age of the house, age of carpet or mattress, keeping of dogs, and Der p 1 concentration was obvious ( 15). These factors largely explained the different Der p 1 concentrations in Hamburg and Erfurt homes.

In contrast to Der p 1, the Der f 1 concentration was less affected by room temperature and humidity. However, the association of Der f 1 concentration and story, age of carpet or mattress, and dog explained only partially the difference between the cities. The difference in Der f 1 concentration in homes of both cities suggests that other, unidentified features of homes may have an influence on the dust-mite microenvironment. Our data exhibit both qualitative and quantitative variations in mite allergens in the two cities and may be also attributed to variation in geography and climate, particularly the humidity of the regions, which varies significantly. Erfurt is considered to have lower humidity in the summer, autumn, and winter, while humidity in the coastal region of Hamburg is comparatively higher, a factor which helps house-dust mites to thrive.

Hirsch et al. studied the exposure to mite allergen in East German dwellings in Dresden, Halle, and Aue shortly after the German reunification (1992–6) and assumed that indoor conditions were not specifically disadvantageous for mite growth in East Germany ( 20). This supposition did not apply to Erfurt homes. The higher proportion of homes with central heating systems in Erfurt (71%) than in Dresden (45.8%) probably biased our data on exposure to mite allergen toward lower values.

Cat-allergen levels

Needless to say, the highest Fel d 1 levels were found in homes that had cats. The cat allergen Fel d 1 was found in 97.5% of homes, and this is in line with the common view that this allergen is ubiquitous in homes, as demonstrated by other studies. It is attached to wall surfaces ( 30) and can be introduced into the home by the occasional visit of a cat or a cat owner ( 31).

In accordance with other studies ( 31, 32) the concentrations of Fel d 1 were higher in dust from living rooms than in dust from bedrooms, but this was only so in Erfurt, where, presumably, either the cats had no access to the bedroom, or the bedrooms were more often or more efficiently cleaned than the living rooms. Similar levels of Fel d 1 were found on floors and mattresses in homes of Hamburg.

Indoor Fel d 1 levels are influenced by ventilation of the homes, but not by the humidity of the area ( 33), although damp homes have been reported to have higher cat-allergen levels ( 17). We found that different factors (ventilation, size of dwelling, and cleaning routines) influence the Fel d 1 levels in dust, but the most important factor was the cat itself. The size of dwelling, the cleaning routines, and cat presence appeared to be the major factors for the different Fel d 1 levels between Erfurt and Hamburg. The higher content of cat allergen in house dust in Hamburg reflects the fact that there are more cats in West Germany.

To summarize, our results are approximately representative of living conditions in Erfurt (East Germany) and Hamburg (West Germany) in the years 1996–7 with respect to main dwelling characteristics. It was found that the level of mite and cat allergens varies between both areas. The higher allergen levels found in Hamburg than Erfurt were mainly caused by different building characteristics (age of home, building material, story, and size of the dwelling) which influenced in part the indoor climate, and other individual living habits (keeping of pets, age of carpets or mattresses, and cleaning routines). Thus, differing housing conditions persisted even 5–6 years after reunification. Since East Germans more and more accept the western lifestyle, we may expect an increase of the indoor allergen exposure in East German homes. The future will show how long it takes the eastern allergen level to reach the western one.


  1. Top of page
  2. Abstract
  3. Material and methods
  4. Results
  5. Discussion
  6. Acknowledgment
  7. References

This study was supported by a grant from the Bundesministerium für Bildung, Wissenschaft, Forschung und Technologie (BMBF/FKZ 01 EE 9301/6).


  1. Top of page
  2. Abstract
  3. Material and methods
  4. Results
  5. Discussion
  6. Acknowledgment
  7. References
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