The U.S. Centers for Disease Control has proposed tightening regulations on air and sea carriers aimed at preventing the introduction of infectious diseases from abroad. This is in response to the outbreak of severe acute respiratory syndrome, or SARS, in 2003.

U.S. health officials responded to the outbreak of SARS two years ago by trying to prevent the entry into the country of airline passengers who looked sick.

But they found the experience of trying to track passengers who may have been exposed to the infectious illness extremely difficult.

Officials say the airlines kept passenger records for only brief periods and they were incomplete, often containing little more than seat numbers to identify passengers.

A review by the agency led the Centers for Disease Control to increase the number of quarantine stations and improve the training and response of public health investigators.

Based on its experience, the CDC is proposing to tighten the reporting rules for communicable diseases.

Martin Cetron, director of the CDC's Division of Global Migration and Quarantine, says the new rules would require airlines and ship operators to keep electronic passenger manifests for at least 60 days and turn them over to public health authorities within a day of a request.

"And these are now requirements that are proposed.. to facilitate public health's ability to intervene swiftly in sort of a 21st century approach, when often there are only hours or days to implement countermeasures, to offer post exposure vaccination, antibiotics and anti-virals, or to separate people who have been exposed from others who are unexposed," he said.

The updated regulations would spell out for the crew members what symptoms to watch out for. For example, Dr. Cetron says passengers with fevers of 38 degrees celsius or greater, with a rash, headaches and neck stiffness, jaundice and changes in levels of consciousness should all be reported to public health authorities.

"What we're looking for is in the subset of occasions where that type of illness not only rings the attention of a flight attendant, but is also likely to be of a communicable nature, and meet these definitions of an ill passenger where the illness is likely to be an infectious disease and one that may be contagious," he said.

The U.S. lists nine diseases that would prevent someone from entering the country. They include pandemic influenza, cholera, diphtheria, infectious tuberculosis, plague, smallpox, yellow fever, viral hemorrhagic fevers and SARS.