Federal health officials say they are stepping up efforts to protect the nation against influenza, amid concerns that bird flu could enter the U.S. from Asia and cause a pandemic.

CDC officials told lawmakers Wednesday that they are moving to more than double the number of quarantine stations used to evaluate and detain travelers from overseas who enter the country ill with potentially dangerous contagious illnesses.

The agency currently operates 11 of the stations near major ports of entry but expects to have 18 operational by the end of 2005 and eventually expand the number to 25, they said.

Officials said the expansion is part of an effort to increase the government's ability to respond to a potential influenza pandemic. Concerns over the potential impact of the flu were heightened this winter amid a widespread shortage of vaccines that left the U.S. with just over half of its expected supply.

Unease has also increased among health officials as bird flu continues to spread among millions of chickens and ducks in Southeast Asia. Wild birds worldwide carry the bird flu virus in their intestines but usually do not get sick from them. However, bird flu is very contagious among birds and can make some domesticated birds, including chickens, ducks, and turkeys, very sick and kill them.

According to the CDC, the bird flu virus does not usually infect humans, but some cases of human infection with bird flu viruses have occurred since 1997. According to the World Health Organization, a bird flu virus known as H5N1 has infected 79 persons and killed 49 in Cambodia, Thailand, and Vietnam since January 2004.

President Issues Executive Order on Flu

Last week, President Bush issued an executive order for the first time adding influenza to the list of diseases for which the government is empowered to detain people in quarantines. A Department of Health and Human Services spokesperson said at the time that the order was part of the government's preparation strategy for bird flu.

Influenza pandemics occur periodically, sometimes with devastating consequences. A pandemic of the Spanish Flu in 1918 killed an estimated 20 million people worldwide.

"People who are expert in influenza do not think it's a question of 'if', they think it's a question of 'when,'" Anne Schuchat, MD, acting director of the CDC's National Center for Infectious Diseases, told members of the House Transportation and Infrastructure Committee.

The H5N1 virus has shown only limited capacity to spread from birds to humans or between humans, an ability that would be key to widespread transmission among humans. But the strain is of particular concern because the U.S. population has essentially no immunity against this virus.

Schuchat said that Bush's executive order is "not an order that we expect to need to use." But, she added, "our area of greatest concern right now is the threat of pandemic influenza."

H5N1 is resistant to amantadine and rimantadine -- antiviral medications used against the flu. According to the CDC, oseltamavir and zanamavir may treat the bird flu caused by the H5N1 virus, but they say studies still need to prove that they work.

Infected birds shed flu virus in their saliva, nasal secretions, and feces, and infections in humans have resulted from contact with infected poultry or contaminated surfaces. Symptoms in humans range from typical flu-like symptoms (fever, cough, sore throat, and muscle aches) to eye infections, pneumonia, and severe respiratory diseases. The illness can be severe and lead to life-threatening complications.

CDC Purchases Bird Flu Vaccine

CDC officials announced several weeks ago that they had purchased 2 million doses of bird flu vaccine. The doses are currently being tested for effectiveness at the National Institutes of Health.

But some lawmakers questioned whether federal authorities are acting quickly enough to counteract the risk of infected persons entering the U.S. from overseas.

Rep. Peter DeFazio, D-Ore., criticized the Federal Aviation Administration for lacking regulations requiring pilots to check the quality of in-plane air before takeoff for the presence of circulating viruses that could increase the risk that passengers transmit flu or other illnesses after entering the U.S. "We're going to wait for after the fact" to develop standards, he said.

Jon L. Jordan, MD, the air surgeon for the Federal Aviation Administration, said that the vast majority of commercial airliners carry advanced filters capable of sifting out viruses and bacteria. "We haven't seen at this point and time a reason to make a requirement," he said.

Rep. William Pascrell, Jr., D-N.J., also criticized the CDC for not releasing a national pandemic flu response plan that has been in draft form since August 2004. Officials said that the plan is still undergoing evaluation and would soon be released to local and state health authorities who will be told to use it to update their flu plans.

"I am extremely concerned that our planning efforts might be overtaken by events," he said.

By Todd Zwillich, reviewed by Brunilda Nazario, MD

SOURCES: World Health Organization, Cumulative Disease Surveillance and Response update, April 4, 2005. Anne Schuchat, MD, acting director, National Center for Infectious Diseases, CDC. Rep. Peter DeFazio (D-Ore.). Jon L. Jordan, MD, flight surgeon, Federal Aviation Administration. Rep. William Pascrell, Jr. (D-N.J.).