Mike Clarke/Agence France-Presse – Getty Images

A mother and daughter on Friday on the subway in Hong Kong.


Published: May 1, 2009


The New York Times, HONG KONG – Swine flu spread to Asia on Friday, as Hong Kong authorities announced the continent’s first case, a 25-year-old traveler who came from Mexico via Shanghai, and immediately quarantined an entire hotel where the traveler had stayed on Thursday night.

The case re-awoke memories of SARS, the severe acute respiratory syndrome that arrived in the territory six years ago, and raised concerns that the virus may have been introduced to mainland China, although the man did not leave the airport while in Shanghai. Flu experts have warned that it would be harder to manage the disease if it becomes established in Asia’s densely populated countries.

Worldwide, the number of confirmed cases of what is now known as influenza A(H1N1) continued to climb. The Centers for Disease Control and Prevention raised its total number of confirmed cases in the United States on Friday to 141 cases in 19 states, up from 109 cases in 11 states a day earlier.

Hong Kong’s first confirmed arrived Thursday afternoon on a China Eastern flight, then checked into a local hotel and fell ill, health officials said in an evening press briefing. Hong Kong authorities responded quickly, quarantining the man at a local hospital, declaring a health emergency, and then quarantining all 200 guests at the hotel, the Metropark, for seven days – whether or not they had contact with the man.

About 100 members of the hotel staff are also being kept in the building, and will be moved to rural campgrounds that are being converted overnight into medical quarantine areas, authorities said. Health workers in blue uniforms and green surgical masks also arrived to distribute boxes of Tamiflu, which is used to shorten the duration of the flu, to hotel guests and staff.

“No one can enter or leave the hotel without the permission of a health officer,” said Dr. Lam Ping-yan, Hong Kong’s director of health.

Despite the alarm the epidemic has raised in Hong Kong and other areas, the epidemic has so far resulted in mild illness in many of those infected outside Mexico, and worldwide caused one death in the United States and fifteen in Mexico. There are 358 confirmed cases of infection in Mexico, believed to be the outbreak’s epicenter, and tests are continuing to see if more of 159 people who recently died of respiratory ailments had the flu, Mexican authorities said.

While it is not yet clear if this new virus is more lethal than seasonal flus, which kill an estimated 250,000 to 500,000 people worldwide each year, some scientists are beginning to argue that the A(H1N1) flu lacks some of the genetic earmarks of a highly lethal strain. Mexican health officials said Friday that the virus is responsive to treatment by Tamiflu and other antiviral medications if they are administered shortly after the disease’s onset, and reported that widespread closures mandated throughout the country appeared to be slowing the disease’s spread.

Yet most people will not have immunity to this new virus, and a vaccine is months away. And even a flu with a low percentage of lethality can cause a large number of deaths if vast swaths of populations are infected.

Worldwide, the number of confirmed cases rose from 257 to 331 Friday, the World Health Organization in Geneva reported.

The organization’s figures remained lower than the sum of confirmed cases reported by individual states and countries because the organization is bound by international rules to report only those cases confirmed to it by specific national laboratories, a spokesman said.

Governments and institutions around the world scrambled to ward off infection. Japan’s sumo wrestling authority will distribute antibacterial liquid hand soap and face masks to athletes and their families, media reports in Japan said. Hong Kong has begun requiring all arriving travelers to fill out health declarations before being allowed to enter the territory.

The Roman Catholic Church in New Zealand instructed priests Friday not to place communion wafers in worshippers’ mouths because of transmission risks, The Associated Press reported, and indigenous Maori were urged to stop using an ancient greeting that brings people nose-to-nose.

No new countries were added to a W.H.O. list released on Friday- Mexico, the United States, Canada, Spain, Britain, Germany, New Zealand, Israel, Austria, the Netherlands and Switzerland. Health officials in Peru, Costa Rica, Denmark have also reported confirmed cases, according to news services. Russia on Friday reported two suspected cases, Interfax reported.

“This is a rapidly evolving situation,” said Dr. Richard Besser, acting director of the Centers for Disease Control and Prevention. “It is a situation filled with uncertainty.”

The Marine Corps said late Thursday that two service members at Camp Pendleton, California, have been confirmed as having swine flu, The A.P. reported, and both were recovering after being isolated. The cases brought the number of confirmed instances of the illness in California to 13.

The C.D.C. reported Friday 50 cases in New York; 28 in Texas; and 16 in South Carolina. The other states with officially confirmed infections were Arizona, California, Colorado, Delaware, Illinois, Indiana, Kansas, Kentucky, Massachusetts, Michigan, Minnesota, Nebraska, Nevada, New Jersey, Ohio, and Virginia.

On Thursday, the White House disclosed that a member of the Obama administration delegation that traveled to Mexico in mid-April probably contracted the disease. The man had flu symptoms when he returned to Washington, and spread the illness to his wife and son, but he and his family have recovered and he is back at work. Robert Gibbs, the White House press secretary, said the man did not work closely with the president and never posed any risk to him.

In Britain, a worker from the National Health service, Graeme Pacitti, 24, who fell ill after being in contact with a Scottish couple who honeymooned in Mexico, was confirmed to have the H1N1 virus, making him the person in Britain to get the flu without having visited Mexico, Reuters reported.

The Scottish Health Secretary Nicola Sturgeon told reporters that, while Mr. Pacitti’s symptoms were not severe, the idea that the virus could be spreading within the country “give us cause for concern.”

The same concerns emerged in Germany. The Health Ministry in Berlin said Friday that swine flu had spread within the country after a Bavarian woman who had not been to Mexico fell ill. She had been in contact with one of three people previously diagnosed with the illness after returning from Mexico. The woman, who was not identified by name, had now recovered, the ministry said.

In Canada, the confirmation of 15 additional cases on Thursday brought the total number of cases there to 34.

On Friday, Mexico implemented its plan to shut down non-essential federal government offices and businesses for five days. The closing of stores and other businesses is meant, in part, to keep people home during a long holiday weekend there when people would normally head out to the beach and to restaurants.

On Thursday evening, Health Secretary José Ángel Córdova said there had been a drop in the number of suspected cases handled by the hospital system of the Mexican Social Security Institute.

“Social Security received 212 probable cases April 20. Today there were only 46. There has been a progressive decline in these cases,” he said.

In the United States, the government continued to roll out the plans it had made to deal with a nationwide outbreak. Until now, states have had to send samples to the C.D.C. in Atlanta to be tested for the new flu strain. But this week, the C.D.C. began sending materials to the states so that they could do their own tests and get results more quickly.

California was among the first to receive the materials, and a spokesman for the state health department said that by the end of the week, the state should be able to do its own testing.

But as health officials kept working in emergency mode, a few infectious disease experts quietly suggested that fears related to the outbreak were overblown.

Dr. Paul Offit, chief of infectious diseases at the Children’s Hospital of Philadelphia, said the death of a 23-month-old Mexican child in Texas did not mean that the outbreak was extraordinarily dangerous.

“Every year we see between 75 and 150 children die of flu, most of whom were previously healthy,” Dr. Offit said.

Recent improvements to the nation’s flu surveillance system led officials to notice the swine flu outbreak, he said, when just a few years ago it would have been lost among the sea of routine sicknesses.

“We’re very quick now to identify new strains of the flu,” Dr. Offit said. “The question is what we should do with that.”

Dr. John Treanor, a professor of medicine at the University of Rochester Medical Center and an infectious-disease expert, said swine flu would probably be only slightly more dangerous than the usual seasonal flu.

“It won’t be severe, although there will be some deaths,” Dr. Treanor said. Because seasonal flu causes about 36,000 deaths a year in the United States, some deaths should not be surprising, he said.

Keith Bradsher reported from Hong Kong and Sharon Otterman from New York. Reporting was contributed by Denise Grady from New York; Alan Cowell from London; Gardiner Harris and Jeff Zeleny from Washington; Elisabeth Malkin from Mexico City; and Ian Austen from Ottawa.


Negative stain electron microscopy image of the swine influenza.

Credit: C. S. Goldsmith and A. Balish, CDC 

Despite some resemblance to the deadly 1918 flu, the swine flu may not be so bad.


MIT Technology Review, May/April 2009, by Emily Singer  —  Scientists studying the genome of the new swine flu virus say that it may not be as bad as first feared.

Public-health officials said today that they expect the virus to continue to spread around the country. However, so far, cases in the United States appear to be mostly mild, meaning that the ultimate public-health toll may be no worse than that of the typical seasonal flu, which kills an average of 36,000 people in the United States each year.

Early analysis of the genome seems to support that idea. According to an article in the Los Angeles Times,

“There are certain characteristics, molecular signatures, which this virus lacks,” said Peter Palese, a microbiologist and influenza expert at Mt. Sinai Medical Center in New York. In particular, the swine flu lacks an amino acid that appears to increase the number of virus particles in the lungs and make the disease more deadly.

Ralph Tripp, an influenza expert at the University of Georgia, said that his early analysis of the virus’ protein-making instructions suggested that people exposed to the 1957 flu pandemic–which killed up to 2 million people worldwide–may have some immunity to the new strain. That could explain why older people have been spared in Mexico, where the swine flu has been most deadly.

At a press conference today held by the Centers for Disease Control, acting director Richard Besser said that it’s premature to say anything about the virulence compared with other strains of influenza based on genetic analysis.

It’s also too soon to say what might happen over time. For example, viruses mutate constantly, so it’s possible that this pathogen could become more deadly. “We are seeing slight changes as it moves through the community, but at this point we can’t say if those changes impact how severe the virus is,” said Besser at the press conference.

The 1918 virus began as a relatively mild flu, but then returned for a more deadly second wave. “If this virus keeps going through our summer, I would be very concerned,” Palese told the Times.

Yes You Can


Catch Flu From Money?

The New York Times, May 1, 2009  —  The influenza virus can survive on paper money for 10 or more days – suggesting that when we shop, spend and bank, there’s more than cash that is changing hands.

The link between flu virus and paper currency is explained this week in a story on SmartMoney.com. The findings don’t mean we should fret about handling currency – but it does illustrate why health officials repeatedly tell people to wash hands frequently. From the SmartMoney report:

Generally speaking, scientists interviewed by SmartMoney estimate the lifetime of a plain flu virus deposited on money at an hour or so. But mix in some human nasal mucus, and the potential for the virus to hang on long enough to find a victim increases, according to one of the few scientific studies done on flu transmission through cash.

In a study conducted at Switzerland’s Central Laboratory of Virology at the University Hospitals of Geneva, researchers tested to see what would happen when flu virus was placed on Swiss franc notes. In some of these tests, researchers placed flu virus mixed in with nasal secretions from children on banknotes -and saw some unexpected results.

When protected by human mucus, the flu cells were much hardier-in some cases, lasting up to 17 days on the franc notes. The virus that persisted for 17 days was a form of influenza A called H3N2. In an e-mail interview, Dr. Yves Thomas said samples of an influenza A strain called H1N1 also endured for quite a bit – in some cases, up to 10 days. That bug was similar but not identical to the virus at the center of the current swine flu outbreak, which is considered a new strain of H1N1.

The story goes on to explain how money could theoretically spread a virus.

Three things must happen for a flu virus to be transmitted from one person to another via money. First, a person who is infected with the swine flu must sneeze or cough onto the bill or blow their nose and leave remnants of their mucus on the currency. Next, an uninfected person would need to touch the money while the virus is still present.

Finally, that person would need to put their contaminated hand in their mouth or pick their nose, says Dr. Murray Grossan, an otolaryngologist at Cedars-Sinai Medical Center in Los Angeles.

A 2002 report in the Southern Medical Journal showed that money can be a vector for more than just flu. Dollar bills collected in western Ohio were tested. The researchers found pathogens, including Staphylococcus aureus and Klebsiella pneumoniae, on 94 percent of the bills.

The SmartMoney story is packed with additional insights about money and germs, explaining why new U.S. dollars may be more resistant to germs than used money (the ink in new bills contains a fungicide), how coins are more likely to be virus free, the development of cash-cleaning ATM machines and why plastic credit cards are a better option during a pandemic. To read the full story, click on “Can You Catch Swine Flu from Money?

And to read the full study on influenza and Swiss francs, check out “Survival of Influenza Virus on Banknotes,” in the May 2008 issue of the journal Applied and Environmental Microbiology.

Can You Catch Swine Flu From Money?

SmartMoney.com, May 1, 2009  —  To reduce the risk of catching swine flu, the Centers for Disease Control and Prevention recommends frequent hand washing and using tissues when you sneeze. But there’s another way to protect yourself -even if it’s not so good for the economy: Stop spending money.

It doesn’t get talked about much, but the fact is paper currency-the dollars, fives, tens and twenties most people routinely touch every day-can spread a virus from one person to another. So if you have contact with money that an infected individual has also handled, there’s a possibility of catching the flu.

How likely is that? Despite the pervasiveness of cash in society, its role in transmitting illness has been the subject of surprisingly little study. But some recent research suggests that flu bugs can show some staying power when they land on one of the countless banknotes that change hands every day.

Generally speaking, scientists interviewed by SmartMoney estimate the lifetime of a plain flu virus deposited on money at an hour or so. But mix in some human nasal mucus, and the potential for the virus to hang on long enough to find a victim increases, according to one of the few scientific studies done on flu transmission through cash.

In a study conducted at Switzerland’s Central Laboratory of Virology at the University Hospitals of Geneva, researchers tested to see what would happen when flu virus was placed on Swiss franc notes. In some of these tests, researchers placed flu virus mixed in with nasal secretions from children on banknotes -and saw some unexpected results.

When protected by human mucus, the flu cells were much hardier-in some cases, lasting up to 17 days on the franc notes. The virus that persisted for 17 days was a form of influenza A called H3N2. In an email interview, Dr. Yves Thomas said samples of an influenza A strain called H1N1 also endured for quite a bit-in some cases, up to 10 days. That bug was similar but not identical to the virus at the center of the current swine flu outbreak, which is considered a new strain of H1N1.

The research suggested that in the real world-where runny noses get wiped by hands that then handle money-flu viruses may have more persistence than previously thought. (Read the full study, “Survival of Influenza Virus on Banknotes,” in the May 2008 issue of the journal Applied and Environmental Microbiology here.)

To be sure, many kinds of frequently touched surfaces could temporarily harbor the flu virus. Broadly speaking, scientists consider the risk of transmission in this way to be low, particularly if hand-washing and other hygiene measures are practiced, says Dr. Philip Tierno, director of clinical microbiology and immunology at New York University’s Langone Medical Center and author of “The Secret Life of Germs.”

Three things must happen for a flu virus to be transmitted from one person to another via money. First, a person who is infected with the swine flu must sneeze or cough onto the bill or blow their nose and leave remnants of their mucus on the currency. Next, an uninfected person would need to touch the money while the virus is still present.

Finally, that person would need to put their contaminated hand in their mouth or pick their nose, says Dr. Murray Grossan, an otolaryngologist at Cedars-Sinai Medical Center in Los Angeles.

As public concern and media hype about the swine flu outbreak grows, it’s remarkable how little the subject of money comes up-and how few people want to discuss it. The CDC wouldn’t discuss the role of money in flu transmission. At the New York State Health Department, spokeswoman Claire Pospisil declined to comment. And when we asked the U.S. Bureau of Engraving and Printing-that’s the government operation that actually manufactures money-a spokeswoman told us that what happens to U.S. dollars once they’re in circulation is beyond the bureau’s control.

Meanwhile, concern about the potential spread of swine flu continues to grow in the U.S. and abroad. On Wednesday, the World Health Organization raised its pandemic alert level to phase 5, one level shy of WHO’s highest readiness. As of Thursday afternoon, there has been one confirmed swine flu death in the U.S. — a 23-month-old Mexican child brought to Texas for treatment. Also as of Thursday afternoon, the tally of confirmed U.S. cases of swine flu stands at 109, measured from when it was first identified as a new strain on April 24. To put those numbers in perspective, an estimated 36,000 Americans die annually from complications related to regular seasonal flu strain, according to the CDC.

Still, if all this has you looking more suspiciously at the folding money you’re carrying around, you could consider relying more on coins. Scientists say those are much more likely to be virus-free since metals like nickel and copper inhibit viruses.

And even the humble dollar bill may have some defenses. The ink on freshly-printed U.S. dollars has a fungicidal agent in it that can inhibit the growth of bacteria and fungi and the influenza virus can be killed more easily because of it, says Tierno. As the dollar gets used and abused – especially with perspiration or water – the strength of the ink weakens, he says.

As for the paper, Peter Hopkins, a spokesman for Crane & Co., the exclusive provider of paper for U.S. currency, says he doesn’t know whether the paper has any antiviral properties, but says it is made out of 75% cotton and 25% linen (he wouldn’t disclose the other elements). Tierno says that those natural fibers can be degraded by fungus. And, therefore, to prevent that from happening, the pulp — like the ink — also includes a fungicidal agent.

One big unknown at the moment is whether the swine flu will continue to mutate and grow stronger, says Dr. Rani Bright, assistant professor of pathology, microbiology and forensic medicine at Philadelphia College of Osteopathic Medicine. If it does, the virus could conceivably survive on dollar bills for an even longer period of time.

When severe acute respiratory syndrome, or SARS, first broke out in China, some researchers expected the virus to survive on currency and other surfaces for just a few hours. Instead, it lasted a few days because it was much stronger than originally anticipated, says Dr. Jean Patterson, chair of the virology and immunology department at the Southwest Foundation for Biomedical Research in San Antonio, Texas.

Even after the spread of swine flu subsides, consumers may want to continue being cautious when handling their cash. Some infectious bacteria, such as Staphylococcus aureus and Klebsiella pneumoniae, can stick to currency for a longer period than viruses, according to a 2002 study that was published by the Southern Medical Journal, titled “Bacterial Contamination of Paper Currency.” Dr. Peter Ender, an infectious diseases physician at St. Luke’s Hospital & Health Network in Bethlehem, Pa., who co-authored the study said that while the average health risks are low, bacteria on U.S. dollars could cause mild or serious illness.

Are there ways to make cash cleaner? One approach: ATMs that sterilize your money. Some years back, just such a machine was marketed in Japan, where cleanliness can be something of a cultural obsession. These “clean ATMs” were manufactured by a Hitachi subsidiary, Hitachi-Omron Terminal Solutions. However, according to Hitachi spokeswoman Lauren Garvey, those machines were not available outside of Japan and are no longer manufactured.

There may be a much simpler solution-if you don’t mind making the credit-card companies richer. Paying by credit card instead of cash could lower your risk of catching a bug, says Patterson. That isn’t because of any special properties of plastic, but because your credit card typically passes through fewer hands than cash-reducing the chance of contact with an infected individual. But don’t throw away your bottle of sanitizing gel. Viruses can still live on your plastic for up to an hour or so, she says.


Are your washing habits spreading germs? (Nancy Wegard for The New York Times)

The New York Times  —  Everyone knows hand washing is important. But a new study shows how washing your hands often, and at the right time, can have a big impact on your family’s risk for getting sick.

Most studies on hand washing focus on medical and food service workers. But this month’s American Journal of Infection Control focuses on washing hands at home as a way to stop infections from spreading. Several studies show hands are the single most important transmission route for all types of infections.

Even though most people know to wash their hands after using the toilet or handling a diaper, studies suggest many people are still ending up with germs, particularly those spread by feces, on their hands after leaving the bathroom or caring for a baby.

One study looked in homes of infants recently vaccinated against polio. After vaccination, the virus is known to shed in the baby’s feces. Researchers found the virus on 13 percent of bathroom, living room and kitchen surfaces. While the virus from the vaccine didn’t pose a health risk, the study shows how feces-borne viruses can travel through the home.

Another study found that in homes where salmonella cases had been diagnosed, the bacteria were still lurking in toilet bowls three weeks after the outbreak. Water splashing on the toilet seat was a source of contamination.

Doorknobs, bathroom faucets and toilet flush handles are key sources of germ transmission in the home. That’s why people should focus on cleaning such surfaces regularly and always wash hands after touching them. In one study, a volunteer touched a door handle that had been contaminated with a virus. He then shook hands with other volunteers, and further tests showed he had spread the virus to six people.

The study authors note that the timing of hand washing is key. It’s obvious to wash hands after using the toilet, after sneezing or before eating or handling food. Other crucial times for hand washing are after changing a diaper or cleaning up after a pet, or after touching garbage cans, cleaning cloths, cutting boards, dish rags and utensils that may have come into contact with raw food.

While it may be hard to believe that something as simple as regular hand washing can make a difference in your family’s health, consider what happened in Hong Kong during a 2003 outbreak of SARS, a severe and potentially deadly form of viral pneumonia. The outbreak triggered extensive public and community health measures promoting basic hygiene, including regular hand washing. Not only was the SARS outbreak contained, but other cases of respiratory illnesses, including the flu, dropped sharply.

Journal List > Appl Environ Microbiol > v.74(10); May 2008


Successful control of a viral disease requires knowledge of the different vectors that could promote its transmission among hosts. We assessed the survival of human influenza viruses on banknotes given that billions of these notes are exchanged daily worldwide. Banknotes were experimentally contaminated with representative influenza virus subtypes at various concentrations, and survival was tested after different time periods. Influenza A viruses tested by cell culture survived up to 3 days when they were inoculated at high concentrations. The same inoculum in the presence of respiratory mucus showed a striking increase in survival time (up to 17 days). Similarly, B/Hong Kong/335/2001 virus was still infectious after 1 day when it was mixed with respiratory mucus. When nasopharyngeal secretions of naturally infected children were used, influenza virus survived for at least 48 h in one-third of the cases.  The unexpected stability of influenza virus in this onbiological environment suggests that unusual environmental contamination should be considered in the setting of pandemic preparedness.


To control influenza outbreaks or a pandemic, it is of utmost importance to identify and characterize the different vectors that could promote influenza virus transmission between humans. The respiratory tract of influenza virus-infected individuals is the main reservoir for the chain of transmission in a community. Based on experiments with animal models and observational field studies, large respiratory droplets are considered to be the most frequent vectors sustaining this transmission (4). However, experimental studies with animals with no direct contact have demonstrated that aerosols also play a significant role. In humans, the hypothesis that there is an aerosol route of transmission is supported by indirect evidence in special circumstances, such as confinement for a prolonged period of time in an airplane in the presence of a patient infected with influenza virus (1, 6, 13, 16, 24). In addition, it has been documented that human influenza A viruses can survive for a prolonged period on different types of surfaces once they are present in the environment. Although controversial (2, 6, 24), the possibility that contaminated surfaces and fomites could act as vectors of transmission needs to be considered in the context of overall influenza pandemic preparedness.


For any environmental contamination to be relevant, the virus should not only remain infectious but also persist at a sufficient concentration to enable it to reach the respiratory tract via finger contamination. Rhinovirus is the most common respiratory virus known to be easily transmitted by this route (12). Whether influenza virus is also commonly transmitted by this route remains a subject of debate (4, 24). However, given that the biological properties of a potential influenza virus pandemic strain have not been established, this route of transmission has to be considered. The severe acute respiratory syndrome coronavirus highlighted the ability of respiratory viruses to act in unconventional ways since environmental contamination by stools played a significant role in some population clusters (3, 15, 18). All these questions should be considered not only from a scientific standpoint. We must also take into account and provide answers to the many possible questions raised by various communities and public health authorities.


We hypothesized that banknotes may be one of various possible influenza vectors and may offer opportunities for infection. In Switzerland, a small country with a population of approximately 7 million, it is estimated that 20 to 100 million banknotes are exchanged each day, and billions of individual notes are exchanged daily worldwide. Here, we report the results of an analysis of the stability of human influenza A and B viruses on banknotes.


The New York Times, May/April 2009, by Donald G. McNeil  —  The flu that is moving through humans appears to have a combination of genes from two normally separate sets of pigs, those from the Americas and from Eurasia, scientists say.

However, it is unknown how those pigs met, and there is not yet any genetic proof that this particular flu was ever in a pig.

And, despite current fears, some geneticists feel this strain may not be very deadly. As it circulates in humans, however, especially in the Southern Hemisphere winter, it could pick up dangerous human flu genes.

The only way to be sure, they say, is to wait and see. But world health authorities hope to have a vaccine soon that will put a stop to the flu’s circulation.

The first conundrum – a swine-type virus that has not yet been found in swine – is readily explained, scientists said. It was first identified in humans just last week, when Canadian and American authorities realized that the flus they had sequenced from sick people in California, Texas and Mexico were the same. No one ever tested pigs for it before, and those tests are just getting under way.

Such quirks are common in disease genetics. In the 1980s, for example, it was not known that the AIDS virus was sweeping Africa because the illness was first found in a few gay men in California, and it took years to find the source virus in chimpanzees.

Now, scientists say, the hunt is on for what is jokingly being called Pig Zero.

“No one that I’m aware of has swabbed pigs for this yet,” Dr. Juan Lubroth, chief of veterinary investigations for the United Nations Food and Agricultural Organization, said Wednesday.

An international team, including Dr. Lubroth’s investigators and some from the World Organization for Animal Health, is in Mexico, planning to go to La Gloria, the location of the first known case involving a human, 5-year-old Édgar Hernández.

Mexican investigators have already visually inspected herds of pigs at the vast factory farms there, Dr. Lubroth said. But a flu strain that sickens humans may not bother pigs, just as the H5N1 avian flu kills chickens but usually not ducks.

It will take some time to swab the pigs’ snouts, fly the samples to a world-class laboratory and sequence it. And even then, Dr. Lubroth said, the La Gloria pigs may not be the key, so his team will scour Mexico’s library of routine swine swabs for matches. The only viral sequences on public databases thus far are human.

The federal Centers for Disease Control and Prevention announced last week that the new virus had pieces of North American swine, bird and human flus and of Eurasian swine flu. Although rumors questioning that are circulating on the Internet, most geneticists believe it is correct.

It is essentially a blend of Eurasian swine flu and North American swine flu, but Western hemisphere strains have had an avian segment on the PB2 gene for at least 10 years and a human component on the PB1 gene since 1993, said Henry L. Niman, a biochemist who tracks flu mutations. “The original report is correct,” Dr. Niman said of the C.D.C.’s analysis. The rumors, he added in an e-mail message, stem from “someone who really doesn’t know how to analyze sequences (or is being misquoted.)”

It presumably is in pigs somewhere, perhaps in Mexico. The 1918 human H1N1 established itself in pigs by 1930. But, as Dr. Niman pointed out, it could be only in humans now – or even in a ferret.

The next question, said Dr. Robert G. Webster, a virologist at St. Jude Children’s Research Hospital, is: “How did this virus get in? Is Mexico importing swine from Europe?”

While movement of live pigs between Canada, the United States and Mexico for fattening and slaughter is routine, legal movement of pigs across oceans is rare. Pigs carry many diseases, so importation requires expensive tests and quarantines. The only reason to bother would be for breeding, not meat.

Even pig semen is restricted, said Kent Parker, swine facility manager at the University of California, Davis. “The boars have to be tested and the facility they live in has to be authorized,” Mr. Parker said. Frozen semen can transmit blue-ear pig disease, he said. It cannot transmit flu, said a spokeswoman for the National Pork Board.

Peter Daszak, president of the Wildlife Trust, found records showing that Mexico imported two pigs from France in 2007, the United States imported a few from Britain and Ireland, and Canada imported hundreds from Europe. “And surely this isn’t the whole truth,” he said. “There must be a hidden illegal trade.”

While some scientists looking at the virus genome debated its origin, Peter Palese, chairman of microbiology at Mt. Sinai School of Medicine, found cause for optimism about the future. All the pandemic viruses of the last century – the 1918, 1957 and 1968 flus – had a mutation in the gene coding for a protein known as PB1-F2 that is thought to make a virus more lethal. The mutation, he said, is not in the new strain.

Dr. Niman, looking at the same sequences, saw a mutation that, at the same position in H5N1, appeared to speed the virus’s spread in Egypt.

Gardiner Harris contributed reporting from Washington.