MEXICO CITY, Mexico (CNN) -- A killer bug is spreading like wildfire.



Armed guards stand outside the Mexico City Respiratory Hospital to control the flow of people.



Streets of one of the world's biggest cities are eerily empty. Bars and restaurants have been shuttered for days.



The president goes on TV to tell workers to stay at home for their own safety.



Those who venture outside are clad in surgical masks. Once healthy people are suddenly falling sick and dying from a new disease, H1N1 swine flu.



The government swears the situation is under control. But down at the hospital, medics scurry around behind the glass door of an isolation ward. They're clad from head to toe in biohazard suits, goggles and two pairs of gloves.



At the airport, officials set up a barrage of thermal imaging machines. If the picture flashes up red or orange, would-be passengers are whisked off to medical facilities.  See where the virus has been confirmed »



It may sound like a sci-fi movie. It's not. Welcome to Mexico City.



It's a nightmare scenario and despite twice-a-day news conferences featuring Mexican Health Minister Jose Angel Cordova, people on the streets fear the virus may be out of control and that the real death toll may be greater than anyone is letting on.  Watch how the city has been shut down »



"The measures we're taking are working and are helping us to slow the spread of the virus. But the situation continues to be serious," Cordova said at a news conference this week.



Government orders to its citizens are clear: wash frequently, don't shake hands or kiss, and stay away from crowded places.



That's easier said than done.



The doors on the subway car snap open at Hidalgo station. Dozens more passengers clad in surgical masks stream on.



It's rush hour deep below the streets of downtown Mexico City.



The subway system is the veins of the capital, ferrying millions of people from all social classes to and from work. It's hot and humid down there and there's little fresh air. It's just the kind of crowded place that Mexican authorities say could be a prime breeding ground for swine flu.



"I'm pretty nervous of this whole virus thing," welder Frontino Valdez mumbled  through one of the masks.  Watch passengers packed onto trains trying to protect themselves »



Sitting one carriage down, Berta Hernandez, a product demonstrator, tries not to show her panic and applies eyeliner like any other morning. But today she has a problem, she has no intention of lifting her mask to paint on lip gloss.



"I'm nervous of those people who aren't wearing masks. Maybe they will suddenly sneeze or cough," she said. In these days of swine flu paranoia, just coughing, or worse sneezing, in the subway, or "metro" as they call it here, brings black looks from fellow passengers.



This has been a strange epidemic since the outset. So far, the Mexican government has been unable to pinpoint where or when this outbreak started.



Authorities admit there was an outbreak of influenza in a village in the Gulf Coast state of Veracruz in early April. But only one patient -- 5-year-old Edgar Hernandez -- was diagnosed as having swine flu.  Watch Dr. Sanjay Gupta ask the boy about his symptoms »



The international media have taken to calling him "Patient Zero." He made a full recovery.



So far there's no evidence a pig farm near his home reported any problems with its livestock. The family hasn't explained how little Edgar could have infected a capital city let alone the world.



The authorities haven't drawn up a genetic map of Edgar's illness nor compared it to the lethal strain that swept through Mexico City and other parts of the country.



Lethal it is. But getting to the truth of who has really died from the virus is tough.



Since midweek, the government abandoned its initial reporting and began to speak only of confirmed
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question: where has they spread?, answer: Mexico City | question: What city  has been hit by the spread of H1N1 ?, answer: Mexico | question: Citizens told not to do what?, answer: don't shake hands or kiss, and stay away from crowded places. | question: what should they not do?, answer: shake hands or kiss, | question: what disease has spread?, answer: H1N1 swine flu. | question: What were the citizens instructed not to do?, answer: shake hands or kiss, | question: Every aspect of life has been hit by the spread of what ?, answer: H1N1 swine flu. | question: What is brought on by the death of a child?, answer: swine flu paranoia,