If you're feeling under the weather, don't automatically blame the sniffling commuter you sat next to on the bus on the way to work. The culprit could be your workplace.
People in developed countries spend about 90 per cent of their time indoors, most of it working eight or more hours in an office without going outside. This makes the modern workplace the new human habitat, which harbours hundreds of different types of bacteria, according to a study.
The joint research between San Diego State University and the University of Arizona tested 90 offices in three cities and found more than 500 species of bacteria, about the same number found in previous studies of bathrooms and aircraft.
Researchers swabbed five surfaces - chairs, phones, computer mouses, keyboards and desktops - and discovered the highest concentrations of microbes were on chairs and phones.
The study, published in an online science journal, PLoS ONE last week, found humans were the main source of bacterial abundance in offices, with skin, oral and nasal cavities harbouring trillions of micro-organisms that can shed and accumulate in work spaces.
''Humans were clearly the primary source of office bacterial contamination,'' the authors wrote. ''Many of the most common genera we discovered inhabit human skin, oral or nasal cavities.''
Not all bacteria are created equal, some are hardier than others.
Professor Peter Collignon, infectious diseases specialist at the Australian National University, said certain microbes die off quickly while those that can reproduce can hang around for years.
''Some can live for quite a long period while others are more susceptible to drying,'' he said.
''How long any bacterium lives depends on how dry it gets and how much light it's exposed to.
''Essentially bacteria like it to be moist and dark.
''You would expect most bacteria on surfaces to die off within hours to days but there will be exceptions to that. Some bacteria have spores which are a bit like seeds. They can keep reproducing for many months if not years.''
Streptococcal species, responsible for conditions ranging from strep throat to meningitis, are susceptible to drying out and dying fairly quickly.
Enterococcus, which can cause urinary tract infections and diverticulitis, can withstand a wide range of temperatures and last for weeks.
Staphylococcus, which has about 40 different species including golden staph, is another robust bacterium, which is slow to dry out. Golden staph can cause a range of illnesses from mild skin infections to pneumonia and meningitis.
Clostridium difficile, which can cause severe diarrhoea, forms spores that are resistant to routine cleaning and can live outside the human body for long periods.
It is impossible to remove every bacterium from all surfaces and it is also unwise, Professor Collignon said.
''A lot of the bacteria we have in our skin and mouths and nose protect us against the more nasty ones,'' he said. ''We don't want to wipe out all bacteria because it's impossible and it will do more harm than good.''
That said, in offices where workers share desks, and colleagues are sneezing and coughing, disinfectant wipes might be handy.
''I don't think people need to use them all the time but you should probably use them if you are sharing equipment,'' Professor Collignon said.