Occurrence of dog, cat, and mite allergens in public transport vehicles


Kirsi Partti-Pellinen, South Karelia Allergy and Environment Institute
FIN-55330 Tiuruniemi


Background and methods: Helsinki City Transport buses, trams, and underground trains carry 687 000 passengers on a weekday. Of the passengers, 0.13% travel with a pet. We interviewed passengers and measured allergen levels in vehicles to study what difficulties allergens cause to passengers with allergy and asthma.

Results: Of 2021 interviewed passengers, 14% complained about inconvenience caused by pets, usually health problems. Of 324 adult passengers with allergy or asthma, 53% had experienced symptoms in public transport; the corresponding figure for 75 children was 32%. The median concentration of the main dog allergen, Can f 1, in dust from seats and floors in public transport vehicles was 2400 ng per g of dust (range 20–8.500 ng/g). For the main cat allergen, Fel d 1, the median was 870 ng/g (range 3–2.600 ng/g). These levels can be regarded as low or moderate, and cause symptoms in sensitive persons. Concentrations of mite allergens were undetectable or low. Allergen levels were lower in vehicles where pets were not allowed than in vehicles where pets were allowed, lower in dust from uncovered seats than in dust from seats with a covering, and lower after cleaning vehicle floors and seats than before cleaning.

Conclusions: Dog and cat allergens are present in public transport vehicles in Helsinki at levels that cause symptoms in sensitive persons. Prohibiting pets would probably bring only a modest reduction in levels, as few pets are carried, and much allergen contamination comes from passengers' clothes.

Public indoor environments such as schools, day-care centres, hotels, cinemas, and public transport vehicles contain allergen reservoirs, which can cause significant exposure to dog, cat, and mite allergens ( 1–4). Allergens in public transport vehicles could be a significant problem, as large populations travel in them daily; Helsinki City Transport buses, trams, and underground trains carry 687 000 passengers on a weekday. The vehicle-operating staff numbers 1200. Pets are permitted, and some 900 passengers (0.13%) per day travel with a pet.

In the present study, we assessed, by means of interviews and questionnaires, the inconvenience caused by pets and allergens to passengers. We also measured dog, cat, and mite allergen concentrations in dust samples collected in vehicles.

Material and methods

Interviews and questionnaires

We interviewed 2021 adult persons travelling in Helsinki City Transport buses, trams, and underground trains from January to April 1996. Every seventh person refused to be interviewed, usually because his or her trip was short. Questions were asked about use of public transport, pets at home, opinion about pets on public transport, inconvenience caused by the pets to the interviewees or their children, and allergies of the interviewees and their children.

Interviewees who suffered from allergy or asthma or who were inconvenienced by pets on public transport were given a questionnaire to be completed and returned by mail. The number of such adults' questionnaires handed out was 751; of these, 56% were returned. Parents who had children with allergy or asthma, or whose children were troubled by pets on public transport, were given the children's questionnaire. The number given was 158, and 47% of them were returned. Questions concerned allergy and asthma symptoms, pets at home, respiratory infections, smoking habits, and opinions about pets and cleanliness on public transport.

The populations are characterized in Table 1.

Table 1.  Characterization of populations
CharacteristicsAdults who
were interviewed
Adults who
Children with
parents who answered
children's questionnaire
Number of persons202142475
 Female (%)657752
 Male (%)352348
Allergy or asthma (%)307660
Smoker (%) 17 
Pet at home (%)262130

Allergens in dust from public transport vehicles

Helsinki buses have upholstered, cloth-covered seats; trams, semihard, cloth-covered seats; and underground trains, uncovered plastic seats. Vehicle floors aredry-vacuumed daily. A wet vacuuming of floors is carried out every 3 or 4 weeks; simultaneously, tram seats are vacuumed and train seats wiped off. Tram seats are washed once a year, bus seats as needed. Pets are allowed on all Helsinki transport vehicles with the exception of every second car in underground trains; these cars have “No pets” signs.

In February 1996, 18 dust samples were collected from seats and floors of vehicles. To collect a sample, a surface of 5 m2 was vacuumed with a 1200-W vacuum cleaner for 5 min with a device that passed the air through a Millipore filter with a pore size of 6 μm (ALK, Denmark), on which the sample was deposited. To get a sufficient sample from train seats, an area of 25 m2 was vacuumed. Samples were stored at −20°C until analysis.

The allergens assayed from the dust samples were the major allergens of dog (Can f 1); cat (Fel d 1); and the three dust mites Dermatophagoides pteronyssinus (Der p 1), D. farinae (Der f 1), and D. microceras (Der m 1). Assays were carried out by ALK in Denmark with the enzyme-linked immunosorbent assay and monoclonal or monospecific antibodies to the major allergens, as previously described ( 1).

Statistical methods

The chi-square test was used to calculate the significance (P values) of differences between studied passenger groups. Allergen concentrations are given as medians and ranges.


Complaints about pets

Of the 2021 persons interviewed, 14% reported that pets on public transport caused inconvenience. Among those who complained, 58% found animals detrimental to their health – they usually had allergy or asthma – 21% experienced animals as frightening, 16% found animals unpleasant, and 5% had some other complaint. Of the interviewees, 30% suffered from allergy or asthma, and 26% had a furred or feathered pet at home ( Table 1). Of those with allergy or asthma, 19% had a pet.

Fifty-one per cent of the passengers who had allergy or asthma and 57% of those with an allergic child were dissatisfied with the present system with few restrictions on the transport of pets. In the opinion of 31% and 36%, respectively, only exceptional pets should be permitted, such as the Seeing Eye dogs of blind persons.


Of the 424 passengers who filled in the questionnaire, 324 had allergy or asthma. Most of these persons reported that they experienced allergy and asthma symptoms when in contact with animals and when on public transport vehicles. The 100 persons who did not have allergy and asthma reported fewer symptoms, but – for instance – 12% experienced nasal symptoms in the presence of animals and 14% on public transport ( Table 2).

Table 2.  Symptoms of allergy and asthma. Passengers and parents of child passengers were asked about symptoms when in contact with animals and when on public transport vehicles
 When in contact with animalWhen on public transport
 Group AGroup BGroup CGroup DGroup EGroup F
 PassengersPassengers PassengersPassengers 
 with allergywith no allergy with allergywith no allergy 
Symptomsor asthmaor asthmaChildrenor asthmaor asthmaChildren
  1. Chi-square test was used to compare group A with group B, and group D with group E; significant differences observed: *P<0.05, **P<0.01, ***P<0.001.

Number of persons3241007532410075
Cough (%)16***31622*1313
Wheeze (%)13***184*00
Feeling of tightness in chest (%)9***246*01
Breathlessness (%)17***2412**21
Sneezing, runny or stuffy nose (%)48***123734***1424
Itching or runny eyes (%)43***82919**613
Itching skin or eczema (%)23***3165*05
No symptoms (%)31***795147***7268

When passengers were asked what caused the symptoms they had on public transport, both persons with and without allergy and/or asthma considered odours from fellow passengers as the most probable cause (62% and 52%, respectively). Among those with allergy and asthma, pets in vehicles placed second as the cause (41%), while few (15%) of those with no allergy or asthma considered pets a probable cause of symptoms. Passengers with a dog or cat at home gave answers similar to those of passengers with no allergy or asthma ( Table 3).

Table 3.  Probable causes given by passengers for allergy and asthma symptoms they experienced on public transport
Assumed cause of symptomsGroup AGroup BGroup C
with allergy
or asthma
with no allergy
or asthma
with dog or cat
at home
  1. Chi-square test was used to compare group A with group B; significant differences observed: *P<0.05, **P<0.01, ***P<0.001.

Number of persons174  2725
Odours from fellow passengers (%) 62* 5276
Pet in vehicle (%) 41**158
Tobacco or cigarette odour (%) 30  2624
Airborne dust (%) 30  3032
Too dry air (%) 21  1936
Draught (%) 10  412
Too humid air (%)  0**44
Other causes (%)  2**114

Allergen levels in vehicles

Dog and cat allergens were found in all seat and floor dust samples examined. The analysing laboratory (ALK, Denmark) described the concentrations observed ( Table 4) as low or medium. Contents of D. pteronyssinus and D. microceras mite allergens were low in all samples, less than 50 ng/g of dust. No D. farinae allergen was found.

Table 4.  Factors affecting levels of dog and cat allergen on public transport vehicles. Dust samples were collected immediately before routine cleaning unless otherwise stated. Allergen amounts are given as nanograms per gram of dust
Factors studied and sites sampledDog allergenCat allergen
of samples
of samples
All samples
Effect of pets – seats
Buses and trams, pets allowed6380020–8500613003–2600
Underground trains, pets allowed12000 170 
Underground trains, pets not allowed1280 142 
Effect of pets – floors
Buses and trams, pets allowed71424–6007112–83
Underground trains, pets allowed2590310–87022018–22
Underground trains, pets not allowed1200 19 
Effect of seat material
Upholstered or cloth-covered seats554002800–850051560670–2600
Uncovered plastic seats21100280–200026042–70
Effect of cleaning – upholstered or cloth-covered seats
Seats before cleaning554002800–850051560670–2600
Upholstered seat after high-pressure120 13 
Effect of cleaning – floors
Floors before daily dry vacuuming720048–8647112–46
Floors after daily dry vacuuming31424–3103227–83

Several factors appear to influence allergen levels in public transport vehicles: allergen levels were lower in dust from uncovered seats than in dust from seats with a covering, lower after cleaning vehicle floors and seats than before cleaning, and lower in vehicles where pets were not allowed than in vehicles where pets were allowed ( Table 4).


Dogs, cats, and, in suitable climates, mites are important sources of indoor allergens ( 1–4). Considerable cat and dog allergen concentrations have been found in dust from public environments, including public transport ( 2), in the UK ( 2, 3) and in Sweden ( 1). In Scandinavia, levels of the mite allergens observed are generally low ( 1, 5–7), and this was true also for the present study. Mite allergens do not – at least not in wintertime – affect the quality of indoor air on public transport. Thus, our study centred on the presence and the effects of dog and cat allergens.

It has been suggested that levels above 8000 ng of the cat allergen Fel d 1 per gram of dust pose both a risk of sensitization and a risk of acute asthma ( 8, 9). For the dog allergen Can f 1, levels above 10000 ng/g have been suggested to be similarly detrimental ( 10). High concentrations of cat (mean 14730 ng/g) and dog (mean 9400 ng/g) allergens have been reported in dust collected from upholstered seats on public transport in the UK ( 2).

The levels of cat (median 870 ng/g, maximum 2600 ng/g) and dog (median 2400 ng/g, maximum 8500 ng/g) allergen in dust from the floors and seats of public transport vehicles in Helsinki ( Table 4) were lower than the risk limits and the levels observed in the UK. The Helsinki concentrations could still be detrimental, as the limits suggested are quite uncertain and low allergen levels may induce hyperreactivity ( 11, 12) and allergy symptoms.

When we interviewed 2021 passengers, 14% reported that animals on public transport caused them inconvenience. The percentage included 8% who said that pets were detrimental to their health, in most cases causing allergy or asthma. It may be noted that the population was large, and the response rate was high (86%).

Of 324 adult passengers who had allergy or asthma, 53% reported that they experienced symptoms on public transport, and 11% attributed the symptoms to animals. Parents with children who had allergy or asthma reported that 32% of the children experienced symptoms on public transport ( Table 2). As the response rates to these questionnaires were only about 50%, passengers who did experience symptoms could be overrepresented, and these percentages could be somewhat too high.

The majority of those with allergy or asthma or with an allergic or asthmatic child wanted restrictions on the transport of pets. Passengers with allergy and asthma considered pets to be the second most probable cause of symptoms; they considered odours from fellow passengers to be the main cause ( Table 3).

In spite of the passengers' opinions, the relative importance of direct exposure to pets appears uncertain. Only 0.13% of passengers travel with a pet. Dog and cat allergens are carried onto public transport both by the pets and on the clothes of passengers and staff. It is known that much cat allergen can be carried on clothing ( 13, 14). As the concentrations of dog and cat allergens were 10–100 times higher in dust from covered seats than in dust from floors, it appears that the allergen contamination of covered seats caused by clothes of passengers is a major cause of exposure. Levels of animal allergen can probably best be lowered by using uncovered seats and by effective cleaning of vehicle floors and seats ( Table 4). Washing the clothes of cat owners has been shown to be an effective method to prevent cat allergen dispersal ( 15).


This work was supported by Helsinki City Transport, the Helsinki Metropolitan Area Council, and the Ministry of Transport and Communications. We thank Fred Björkstén for his critical review during the preparation of the manuscript.