Remember, wear a face mask,” were my doctor's final words to me before I boarded the aircraft to Mexico City.

I had called him in the middle of the night over the weekend as I was packing my bags, to ask if there was anything I should take to ward off a potentially lethal new strain of swine influenza. You feel a bit silly, waking a doctor to ask that kind of question, especially when he doesn't have a clue what you're talking about because he hasn't been watching the news.

He soon got the end-of-the-world gist, however. And thanks to the marvel of American medical capitalism, I was able to collect a suitcase full of Tamiflu and various other hospital-grade medications from a 24-hour pharmacy on the way to the airport. I also picked up some surgical masks. “You're the ninth person to buy these things since midnight,” scolded the cashier. “Now we're out of them. Is there some kind of zombie fever going around?”

“Swine flu,” I explained.

“I thought only people going to Mexico had to worry about that,” came the reply, accompanied by an expression that said, “and clearly only a complete idiot would go to Mexico”.

The Mexicana Airlines terminal was packed. So much for swine flu panic, I thought. After the usual magazine-browsing ritual I checked in and made my way slowly to the gate. By the time I got there I realised that the crowd downstairs had been going to Cancún. The flight to Mexico City was a little less busy. When the boarding call came, all five of us got on the aircraft.

No one said anything. Bringing up the subject of the flu would have been like striking up a conversation about the 9/11 suicide bombers. Better to pretend that everything's just fine.

Soon after take-off I remembered my doctor's advice and reached for my 25-pack of Medline earloop surgical-grade masks (“98 per cent effective!” boasts the packaging, as if the missing 2 per cent isn't a biggie). But then I realised something: no one else on the aircraft was wearing facial protection. This presented a curious etiquette problem. If I put on the mask, I would freak everyone out. I might as well stand on my chair and shout: “Plague! Plague! Arrrgghh!” Also, by putting on the mask I would effectively be declaring my passengers (all of them Latinos) to be unclean. I would look like a neurotic, paranoid, hypochondriac - which, of course, I am, but I try to avoid broadcasting it to strangers.

So in the end I just sat there breathing in the tinned air until I concluded that the mask wouldn't do me any good anyway. Which goes to prove what I've long suspected - good manners can kill you.

Getting the shakes

The issue of bio-apocalypse etiquette gets even trickier when you begin mingling with the locals in Mexico City. Some wear the masks all the time, even when eating. Others don't bother. Likewise, some will still offer a handshake. Others will throw up their hands in air if you so much as turn your palm in their direction.

In many ways this new social interaction is an obsessive compulsive/germophobe's dream come true. It is now completely acceptable to carry antiseptic wash around with you at all times, wear rubber gloves and refuse to come within 5ft of other human beings. Personally, I can't handle keeping the mask on all the time: I feel ridiculous wearing it when talking to someone without facial protection. The death toll, after all, is still only in the low hundreds, in a country with a population of 110 million.

In an act of defiance, I even shook someone's hand on Monday. But then I couldn't sleep for worrying about it.

Class issue

One thing I've noticed: the higher social classes seem more reluctant to wear masks than, say, the bellboys and janitors who staff my almost completely empty hotel. According to one of my local friends, this is because the rich assume that they will be treated at a private hospital and survive, while the poor know that by the time they convince an overcrowded state-run emergency room to give them any Tamiflu, it will probably be too late.

Medical history

My doctor in Los Angeles might not have heard of the swine flu outbreak when I called him on Sunday, but he is, nonetheless, an expert - his grandfather contracted the infamous Spanish influenza of 1918-19, and, against all odds, survived.

His story doesn't offer much reassurance, however. “As soon as he got over the initial flu he ended up getting encephalitis lethargica - ‘sleepy sickness' - which caused his brain to slowly deteriorate,” he told me. “It took him ten years to die, which was very hard on my father when he was growing up.”

All things considered, I think I'll be wearing that face mask on the flight home.

Times Recommends

• Darling won't pay for Brown give-away
• Believe it or not, Big Brother is your friend
• E-mails were quoted out of context