Early Action Key to Halting Spread of Avian Flu From Human to Human

PARIS — To avert a worldwide pandemic sparked by a mutation of an infectious avian influenza, public health officials will need to begin containment efforts before it has spread to 50 humans and treat new cases within 2 days of infection, according to an expert who has developed a mathematical simulation of a potential pandemic.

If a form of the H5N1 virus that is more infectious to humans spreads outside an initial disease cluster, there is little public health authorities can do to keep it out of their countries, said Simon Cauchemez, Ph.D., of the division of epidemiology, public health, and primary care at Imperial College, London.

“For containment, the only option is to act very quickly at the source. Obviously, once the pandemic is international, you can't try to stop it. You can only decrease its magnitude. There's an option for containment at the source, but it will be very difficult to implement,” he said at the international conference on avian influenza in humans.

The simulation assumes any new pandemic strains would have the same transmission rates as earlier infections, including the 1918–1919 Spanish flu pandemic, he said.

Dr. Cauchemez's model assumes the outbreak originates in rural Southeast Asia, where in many cases, the H5N1 virus is endemic among birds. He noted that he designed the model to offer international public health authorities a way to contain the disease to a single geographic region, and if that fails, to help others control the size of the pandemic in their countries once it reaches them.

For now, the disease has been restricted largely to poultry and wild birds.

Most human infection results from close contact with birds. So far, 229 people have been infected, and 113 have died, according to data from the World Health Organization released July 4.

The World Health Organization has documented at least one case of human-to-human transmission. WHO officials do not believe that there was a mutation that made the virus any more transmissible between humans.

But it is feared that the H5N1 virus eventually will mutate into a human-transmissible form. Because it is different from the seasonal form of flu and because health officials cannot predict the genetic makeup of a human-transmissible form of H5N1, vaccinating the population to prevent the spread of the disease is unlikely until the virus has already begun passing from human to human.

In the first affected country, the time from the first human-to-human case to the peak of the outbreak would be between 80 and 120 days, Dr. Cauchemez said.

Beyond treating the influenza cases in an initial outbreak cluster, if an outbreak is to be contained, public health officials need to consider actions such as prophylaxis of the flu patients' households, as well as the population in an area surrounding the flu patients. Other options that might be much more unpopular include closing schools to limit the spread of the virus and quarantining the entire region of an initial outbreak.

To contain an initial cluster of human-spread flu, officials must respond to an outbreak before it spreads to 50 people, new cases must be treated within the first 2 days, 3 million doses of antiviral medications must be available, and public health officials must act in multiple countries, Dr. Cauchemez said.

The simulation indicates that limiting the spread of disease once it enters a country will not be particularly effective, Dr. Cauchemez said. Once a country has an outbreak, the number of people infected with the flu is expected to increase by 10 times in a week or two, so “therefore if you succeeded in decreasing the number of cases 10-fold, you only buy 1 or 2 weeks,” he said.

The only way to prevent avian flu from entering a country is to keep out 99% of those people traveling from areas already affected by the pandemic, Dr. Cauchemez said. “So travel restrictions must be very, very effective—draconian—to have any significant impact,” he added.

Once avian flu enters a country, prophylaxis of a population near a disease cluster, closing schools and workplaces to limit the opportunity for the virus to spread, and prevaccinating children under age 16 would reduce the number of cases but not prevent the spread of the virus, Dr. Cauchemez said.

PARIS — To avert a worldwide pandemic sparked by a mutation of an infectious avian influenza, public health officials will need to begin containment efforts before it has spread to 50 humans and treat new cases within 2 days of infection, according to an expert who has developed a mathematical simulation of a potential pandemic.

If a form of the H5N1 virus that is more infectious to humans spreads outside an initial disease cluster, there is little public health authorities can do to keep it out of their countries, said Simon Cauchemez, Ph.D., of the division of epidemiology, public health, and primary care at Imperial College, London.

“For containment, the only option is to act very quickly at the source. Obviously, once the pandemic is international, you can't try to stop it. You can only decrease its magnitude. There's an option for containment at the source, but it will be very difficult to implement,” he said at the international conference on avian influenza in humans.

The simulation assumes any new pandemic strains would have the same transmission rates as earlier infections, including the 1918–1919 Spanish flu pandemic, he said.

Dr. Cauchemez's model assumes the outbreak originates in rural Southeast Asia, where in many cases, the H5N1 virus is endemic among birds. He noted that he designed the model to offer international public health authorities a way to contain the disease to a single geographic region, and if that fails, to help others control the size of the pandemic in their countries once it reaches them.

For now, the disease has been restricted largely to poultry and wild birds.

Most human infection results from close contact with birds. So far, 229 people have been infected, and 113 have died, according to data from the World Health Organization released July 4.

The World Health Organization has documented at least one case of human-to-human transmission. WHO officials do not believe that there was a mutation that made the virus any more transmissible between humans.

But it is feared that the H5N1 virus eventually will mutate into a human-transmissible form. Because it is different from the seasonal form of flu and because health officials cannot predict the genetic makeup of a human-transmissible form of H5N1, vaccinating the population to prevent the spread of the disease is unlikely until the virus has already begun passing from human to human.

In the first affected country, the time from the first human-to-human case to the peak of the outbreak would be between 80 and 120 days, Dr. Cauchemez said.

Beyond treating the influenza cases in an initial outbreak cluster, if an outbreak is to be contained, public health officials need to consider actions such as prophylaxis of the flu patients' households, as well as the population in an area surrounding the flu patients. Other options that might be much more unpopular include closing schools to limit the spread of the virus and quarantining the entire region of an initial outbreak.

To contain an initial cluster of human-spread flu, officials must respond to an outbreak before it spreads to 50 people, new cases must be treated within the first 2 days, 3 million doses of antiviral medications must be available, and public health officials must act in multiple countries, Dr. Cauchemez said.

The simulation indicates that limiting the spread of disease once it enters a country will not be particularly effective, Dr. Cauchemez said. Once a country has an outbreak, the number of people infected with the flu is expected to increase by 10 times in a week or two, so “therefore if you succeeded in decreasing the number of cases 10-fold, you only buy 1 or 2 weeks,” he said.

The only way to prevent avian flu from entering a country is to keep out 99% of those people traveling from areas already affected by the pandemic, Dr. Cauchemez said. “So travel restrictions must be very, very effective—draconian—to have any significant impact,” he added.

Once avian flu enters a country, prophylaxis of a population near a disease cluster, closing schools and workplaces to limit the opportunity for the virus to spread, and prevaccinating children under age 16 would reduce the number of cases but not prevent the spread of the virus, Dr. Cauchemez said.

PARIS — To avert a worldwide pandemic sparked by a mutation of an infectious avian influenza, public health officials will need to begin containment efforts before it has spread to 50 humans and treat new cases within 2 days of infection, according to an expert who has developed a mathematical simulation of a potential pandemic.

If a form of the H5N1 virus that is more infectious to humans spreads outside an initial disease cluster, there is little public health authorities can do to keep it out of their countries, said Simon Cauchemez, Ph.D., of the division of epidemiology, public health, and primary care at Imperial College, London.

“For containment, the only option is to act very quickly at the source. Obviously, once the pandemic is international, you can't try to stop it. You can only decrease its magnitude. There's an option for containment at the source, but it will be very difficult to implement,” he said at the international conference on avian influenza in humans.

The simulation assumes any new pandemic strains would have the same transmission rates as earlier infections, including the 1918–1919 Spanish flu pandemic, he said.

Dr. Cauchemez's model assumes the outbreak originates in rural Southeast Asia, where in many cases, the H5N1 virus is endemic among birds. He noted that he designed the model to offer international public health authorities a way to contain the disease to a single geographic region, and if that fails, to help others control the size of the pandemic in their countries once it reaches them.

For now, the disease has been restricted largely to poultry and wild birds.

Most human infection results from close contact with birds. So far, 229 people have been infected, and 113 have died, according to data from the World Health Organization released July 4.

The World Health Organization has documented at least one case of human-to-human transmission. WHO officials do not believe that there was a mutation that made the virus any more transmissible between humans.

But it is feared that the H5N1 virus eventually will mutate into a human-transmissible form. Because it is different from the seasonal form of flu and because health officials cannot predict the genetic makeup of a human-transmissible form of H5N1, vaccinating the population to prevent the spread of the disease is unlikely until the virus has already begun passing from human to human.

In the first affected country, the time from the first human-to-human case to the peak of the outbreak would be between 80 and 120 days, Dr. Cauchemez said.

Beyond treating the influenza cases in an initial outbreak cluster, if an outbreak is to be contained, public health officials need to consider actions such as prophylaxis of the flu patients' households, as well as the population in an area surrounding the flu patients. Other options that might be much more unpopular include closing schools to limit the spread of the virus and quarantining the entire region of an initial outbreak.

To contain an initial cluster of human-spread flu, officials must respond to an outbreak before it spreads to 50 people, new cases must be treated within the first 2 days, 3 million doses of antiviral medications must be available, and public health officials must act in multiple countries, Dr. Cauchemez said.

The simulation indicates that limiting the spread of disease once it enters a country will not be particularly effective, Dr. Cauchemez said. Once a country has an outbreak, the number of people infected with the flu is expected to increase by 10 times in a week or two, so “therefore if you succeeded in decreasing the number of cases 10-fold, you only buy 1 or 2 weeks,” he said.

The only way to prevent avian flu from entering a country is to keep out 99% of those people traveling from areas already affected by the pandemic, Dr. Cauchemez said. “So travel restrictions must be very, very effective—draconian—to have any significant impact,” he added.

Once avian flu enters a country, prophylaxis of a population near a disease cluster, closing schools and workplaces to limit the opportunity for the virus to spread, and prevaccinating children under age 16 would reduce the number of cases but not prevent the spread of the virus, Dr. Cauchemez said.