And in the United States, a spokesman for Ford, which has been researching the subject with the University of Michigan, says: "Vehicle cabins are exposed to a wide variety of environmental conditions that can make them microbial breeding grounds."
Researchers found that high mileage made things worse. That taupe upholstery might literally make you chunder. Apart from interiors just gathering gunk with age, air and heater filters are likely to have stopped working properly, letting through airborne microbes.
Children and pets are most at risk from dirty cars, the scientists concluded. However, cars that regularly transport kids and pets were found to have the highest bacteria counts.
Microbiologists at the Aston University in Birmingham studying in-car hygiene found harmful bacteria like E. coli, salmonella, and campylobacter, all of which can cause illness or, on occasion, can be fatal. Each has the capability to survive for a month inside the car on surfaces such as the steering wheel, gear lever or dashboard.
In all, the scientists found 283 different kinds of bacteria per square centimetre in the average car. Extreme cases had 850 types of bacteria per square centimetre.
The gear lever was the most heavily infected part of the passenger area with 356 microbes per square centimetre.
However, another study, by scientists at London's Queen Mary University, found the car boot was the filthiest area.
Other hotspots: car mats, the driver's seat, between the seats, and air conditioning vents.
Don't just blame kids and dogs. About a quarter of those surveyed admitted that food wrappers and empty drink bottles litter their car. One in six said they regularly left or dropped bits of food.
Bacillus cereus - a bug that can cause food poisoning and is found in rice, pasta, potatoes and pies - was commonly found by researchers.
At least half the respondents said the level of cleanliness in their car left "a lot of room" for improvement and that they would never allow their home to be so filthy.
But has the research only proved what we already know?
It seems that motorists have already twigged to the menace of mobile micro-organisms. Market research suggests Americans alone spend more than $2 billion a year on stuff to freshen their cars, including aerosols, plug-ins, slow-release and hanger products that dangle from mirrors.
Driven couldn't find similar statistics for New Zealand, but the shelves of car accessory retailers suggest we're right in there in the war on unhygienic interiors.
The trouble with the aftermarket barf-busters is that some drivers and passengers are sensitive to chemicals or don't like artificial scents.
So researchers are looking for ways to stop making people sick without the solution also making them sick.
"Our findings suggest car interiors are complex ecosystems that house trillions of diverse micro-organisms interacting with each other, with humans, and with their environment," said Blaise Boles, an assistant professor in the University of Michigan's department of molecular, cellular and developmental biology.
In the hunt for a bacteria buster, the team focused on three commonly used Government-approved antimicrobial additives, including silver-ion, ammonium salt and polyolefin wax with a nano-silver coating.
Panels painted with four different formulations were evaluated to assess the growth rates of micro-organisms.
Parts coated with paint infused with the silver-ion additive, sold under the trade name Agion in the US, contained lower microbe growth than control parts with the current type of paint.
Agion, based on elemental ions, works by starving, sterilising and suffocating the microbes to prevent them from growing and reproducing.
Even after many simulated years of use, the microbe growth of the Agion-infused coating was little changed.
The additive had little impact on the gloss and colour change of the surfaces over the test period.
"We can't control everything that contributes to stains and odours in our cars and trucks," said Peters. "But we're doing our part to maintain a pleasant cabin environment for our customers over the long haul."
