The BBC's Matthew Price arrived in Mexico as news of the swine flu outbreak emerged and found a sense of uncertainty over how lethal it is and how quickly it may spread.
Some experts are sceptical about the amount of protection masks can offer
It was raining when we touched down in Mexico City. A light, warm rain that made the tarmac smell musty.
There are many times as a foreign correspondent when you have no idea what to expect on arrival, but this felt very different indeed.
In the bus to the arrivals lounge I noticed two young children wearing facemasks. So were their parents.
The passengers looked around at one another, working out what they should do.
Someone coughed. We laughed a little, but everyone must have been thinking the same thing.
I pulled the facemask I had brought with me out of my bag. Toyed with it, felt a little silly, and put it on.
The danger here does not feel quantifiable.
Mexico City's mayor has put the cost to the economy at $88m (£59m) a day
You know when someone raises a gun that you should leave. That when you approach a frontline you should get ready.
In the last few days I have not had a clue whether I have been at risk or not.
Mexico City clearly felt the same. It had not shut down, but many people were anxious.
They were still going to work, getting onto buses, eating at restaurants. Not as many as usual to be fair, but the city was still functioning.
It looked normal, but then you would see them: the woman at the newspaper stall, a blue surgical mask pulled over her nose and mouth, the doctors tightening the elasticated straps as they walked into hospital.
Then there were the office workers, their breath pulling the fabric tight over their mouths, then ballooning it out as they walked.
Even in cars with the windows rolled-up, the driver, alone in the vehicle, wore a mask covering their lower face.
Most of the time I have not been thinking about the virus. I have just been trying to work out when the discomfort of wearing the mask in this heat and at this altitude outweighs the risk of not wearing it.
Right now, as I say this, I may be carrying the virus. I do not think I am. Only two people I remember in the last few days have coughed anywhere near me, and I was covered at the time.
I have been cleaning my hands, and not touching my face all week. But this is unknown territory.
The BBC's safety team has sent advice. Anyone going to an affected area should not go back into a BBC office within a week of leaving it in case they are infected.
Everyone on the team I am with is already wondering about what that means for their families. Multiply this across a nation of a 100 million and you get a sense of what this country is like at the moment.
From the capital we flew down to Oaxaca where the first confirmed death occurred.
It is a beautiful Spanish colonial town. Its buildings painted red, orange, light green, blue. The cobbles on its streets worn smooth by centuries of traffic.
I met Beatrice Mann from Paris next to a stall where bright multi-coloured thread blankets were hanging.
"I don't really know anything about the flu," she told me with a smile.
She had become more worried when she had seen people wearing facemasks, but she was not thinking of leaving Mexico early.
When I finished interviewing Beatrice I thanked her.
"What do you know about the flu?" she asked.
I told her about the deaths in Mexico, about the handful of people in Europe infected, about the hundreds of students thought to be affected in New York's schools. Her eyes widened.
Her travelling companion started to take notice. I told them they simply needed to take precautions, watch out for people sneezing, avoid enclosed areas. I offered them two face masks. They took them.
Several hours later we were leaving the hotel, heading south to the farm that some believe is where this outbreak started.
Beatrice came up to me, her facemask on tight, white translucent latex gloves on her hands. She looked pale, and worried. "Do you have any more masks, for my friends?" she asked.
She told me they had cancelled the rest of their holiday. She said that the French consulate had told them to stay in Oaxaca, to go straight to the airport for their flight, to leave when they could.
I tried to reassure her.
"But if we get it, how can we leave?" she said. "They won't let us go back."
I paid up, and loaded my bag into the back of our van.
One colleague was wearing a mask, two were not. I put mine on.
A member of staff in a starched blue shirt tucked into pressed black trousers came out of the hotel. "My manager says we cannot wear masks," he said. "It's not good for the visitors to see."
Then he turned to me, slightly embarrassed and a little worried, I felt. "Should I wear one?" he asked.
From Our Own Correspondent was broadcast on Saturday, 2 May, 2009 at 1130 BST on BBC Radio 4. Please check the
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