There is a scene in the American sitcom Curb Your Enthusiasm that now appears surprisingly prescient, given the current anxiety about avian flu.

Larry David and Ben Stiller are being introduced on the set of The Producers when Stiller sneezes, and tries to catch the spray before extending a handshake.

David pointedly ignores the proffered hand, anxious not to become contaminated with Stiller’s germs, but in the process clearly offending him.

Even a few weeks ago we might have thought David’s behaviour unnecessarily rude, but with dead parrots making the fear of a flu pandemic more immediate, the way we treat the potentially infectious may have to change. For if avian flu “learns” how to infect humans, like other flu it will be spread in the particles of saliva expelled through coughing and sneezing. A sneeze can travel at 80 miles an hour, reaching distances of up to 30ft away. Just one sneeze can project 100,000 flu particles into the air.

How long those particles survive depends on the type of virus and the environmental conditions. Flu viruses can survive for more than 24 hours but for even longer indoors in winter because indoor air is more humid.

Professor John Oxford, a virologist at St Bartholomew’s and the Royal London Hospital, has looked at the most effective methods of preventing the transmission of colds and flu and says that, as well as vaccines and antiviral drugs, personal hygiene should be a priority.

“Over the past few decades there has been a worldwide general decline in levels of hygiene. We’ve seen the effects that this can have with MRSA, which focused attention on hygiene in hospitals. The levels of hygiene in hospitals were a reflection of the general situation and we all need to get our houses in order if we are to reduce the spread of infectious diseases.”

A man you’d expect to catch every cough, cold and nasty virus doing the rounds is Professor Ron Eccles, director of the Common Cold Centre in Cardiff. Yet, despite being surrounded by coughing, spluttering volunteers, he suffers only one or two colds a year, a fact he attributes to regular handwashing and avoiding touching his face.

“You’d have to be a hermit never to catch a cold, but in experimental conditions when healthy volunteers are kept with others who are suffering from common cold infections it has proven remarkably difficult to spread infection from one person to another. Most colds are caught at home, because of increased proximity and duration of exposure to the virus.”

In his view, it would be “rude” to offer a “mucus-laden handshake”. “If someone did whether I accepted it or not would probably depend on their status. In any case, I would wash my hands at the first opportunity.”

To catch a cold or flu virus, the mucus from the respiratory tract of someone infected has to get directly into your own respiratory tract. If an infected person coughs or sneezes near you, the risk is that you inhale their infected droplets; alternatively you touch a surface on which these droplets have landed, picking up the virus on your fingers, and then by rubbing your eyes or touching your nose, deposit the virus in your own respiratory tract.

Studies have shown that a cold or flu virus can survive on human hands for several hours. The virus can also survive up to 48 hours on non-porous surfaces such as a telephone, computer keyboard, doorknobs, kitchen utensils or toys. This is what makes handwashing so important. By washing your hands frequently and not touching your face, Professor Oxford says, you reduce the incidence of respiratory disease by 40 per cent.

The Health Protection Agency has not issued specific advice for avian flu; however, its general advice for avoiding infections includes washing your hands after blowing your nose, coughing or sneezing — you should wash more frequently if someone in your home or workplace is sick.