Men of the north, hang your heads in shame. Spot checks on commuters have revealed that the further north men live, the dirtier their hands.

In Newcastle, swabs of men's hands revealed more than half were contaminated with bacteria normally found in faeces.

The percentage of the unclean fell with latitude, with 34% of Liverpudlian men testing positive for faecal bacteria, 21% in Birmingham, 15% in Cardiff and 6% in London.

The findings are part of a study by scientists at the London School of Hygiene and Tropical Medicine into the nation's hand-washing habits, which was designed to highlight how infections can easily be spread by people failing to observe basic rules of hygiene.

Researchers approached 409 commuters waiting at bus stops outside major train stations in the five cities. Swabs of their hands were sent back to a laboratory, where any bacteria on them were grown and identified.

"When we first saw this north-south divide we scratched our heads. We thought it might be something to do with the way we did the tests, the weather, or the time it took to get the samples back to the lab, but the issue is with the men, not the women, so it must be a difference in behaviour. The best I can think of is that men in the north are too tough to wash their hands. We need to investigate it more, it's puzzling," said Val Curtis, director of the school's hygiene centre.

Overall, 28% of people who agreed to a swab tested positive for faecal bacteria, such as Enterococcus, E coli, Klebsiella and Panteoa. The types of bacteria rarely cause serious infections, but their presence has alarmed scientists none the less.

"I was expecting to find around five to 10% of people with faecal bacteria on their hands, so I was flabbergasted at the number. It means people aren't washing their hands after using the toilet, that they are contaminated and leave their bugs on surfaces where other people pick them up," Curtis said.

The study, which is preliminary and has yet to be published, found that female hygiene was more consistent than that of males. On average, 27% of women had faceal bacteria on their hands, with Londoners again the cleanest at 21% and Liverpudlians the dirtiest at 31%.

The study has been released to coincide with Global Handwashing Day, a public-private partnership set up to promote hand washing with soap to reduce diarrhoea and other infections in developing countries.

"These bugs just shouldn't be on peoples' hands. If someone has a pathogen in them, such as rotavirus or Salmonella, this is a superhighway for passing it around to the community," Curtis said. "Just rinsing your hands under the tap doesn't remove bacteria, because they tend to get stuck in any dirt and grease you've got on your hands."

The study found that people who used the bus were nearly twice as likely to test positive for faecal bacteria than train commuters. Bacteria can live for two to three hours on surfaces after being touched by a contaminated hand.

Worldwide, around 1.9 million people die from diarrhoea every year. In Britain, an estimated one in five has an episode of diarrhoea each year.

Mike Catchpole, director of the Health Protection Agency's Centre for Infections, said: "Hand washing is one of the most important ways of controlling the spread of infections, especially those that cause diarrhoea and vomiting, colds and flu.

"Global Handwashing Day serves as a timely reminder that people should always wash their hands after using the toilet, before eating or handling food, and after handling animals. And remember to cover all cuts and scratches with a waterproof dressing." HPA figures suggest that cases of norovirus, the winter vomiting bug, are rising and that the annual norovirus season is likely to have begun already. Norovirus is the most common cause of gastrointestinal disease in the UK,with the number of cases peaking between October and March. Between 600,000 and a million people in the UK are affected each year.

• This article was amended on Thursday October 16 2008. In the article above we stated that: "Worldwide, around 1.9 million people die from diarrhoea every day". We meant to say, every year. This has been changed.