Federal investigators have begun warning several hundred passengers who took United Airlines flights from Baltimore to Chicago and from Chicago to Honolulu on May 11 that they may have been exposed to tuberculosis by a woman who died of TB after her arrival in Hawaii.
Several infectious disease specialists said yesterday the risk that she infected other passengers on the two flights is small because the disease is usually spread among people -- such as family members -- who have spent prolonged periods of time in close proximity.
Nonetheless, they said that the risk may have been heightened somewhat by the confined quarters of an airline cabin and the tendency of modern air-handling systems to circulate stale air along with fresh air from the outside.
The woman, a native of Korea who lived in Japan for the last 12 years, spent about a month visiting friends in Howard County before boarding United Airlines Flight 493 at BWI. In Chicago she changed planes to United Flight 47, then landed in Hawaii so sick that she was hospitalized immediately.
Tuberculosis is a bacterial disease spread in airborne droplets by coughing, sneezing and -- in some cases -- talking. The disease, which usually attacks the lungs, causes chest pain, shortness of breath, fever, sweating and poor appetite.
Several years ago, the woman was treated for tuberculosis, a state official said, and the condition resurfaced around the time she visited the United States. She was bedridden with a severe cough and other respiratory symptoms for her entire time in Maryland but did not seek medical attention.
"Clearly, she was very much in the extreme in not receiving medical evaluation for a very serious health problem," said Sarah Bur, who heads tuberculosis control for the Maryland Department of Health and Mental Hygiene.
Antibiotic treatment usually prevents serious complications and death -- and keeps people from spreading the disease to others. Officials with county, state and federal health agencies said they had no idea why the woman did not seek treatment.
The family she was visiting did not know she was suffering from tuberculosis until they learned about her hospitalization, officials said. On May 23, the family contacted the Howard County Health Department -- a call that triggered involvement by the state health department and the federal Centers for Disease Control and Prevention in Atlanta.
Ruth Talbot, director of nursing for Howard County, declined to say where the family lived or to release any other personal information. The family, which has been free of any symptoms, is currently undergoing tests to determine if anyone harbors a silent infection.
Recently, investigators with the CDC started calling people who were on the two flights to tell them they should consult their doctors and get tested for possible exposure to tuberculosis.
Letters with additional information will be sent in a few days, a CDC spokeswoman said yesterday.
A United spokesman would not say how many passengers boarded in Baltimore or in Chicago. Joseph Hopkins, the spokesman, said the CDC recently asked United for the names of passengers on both flights. "We provided the information to them," he said.
This was the first time the CDC had requested such information from United, he said.
"We were not aware that a passenger with such a disease was boarding the plane," said Mr. Hopkins. "We certainly would have had to talk to our medical department and decide whether to allow the passenger to board."
The first plane was either a Boeing 737, which carries a maximum of 108 passengers, or a Boeing 727, which can accommodate 147. The Hawaii-bound plane was a Boeing 747, which carries 393.
The flight to Chicago lasted about two hours, and the flight to Honolulu about nine hours.
The first plane appeared to be about three-quarters full, said a Seattle man who was on board. Dean Thomas Rutz said a CDC agent told him Tuesday that a coughing passenger subsequently died of TB. Mr. Rutz was advised to consult a doctor and get a skin test.
"He didn't go into the probability of risk, only that there was the potential of risk," Mr. Rutz said. "I guess I'm a little worried, but not overly so. It does really kind of make you wonder about the spread of bacteria, especially when you consider that you can be exposed to several hundred passengers" on a plane.
"Tuberculosis is not very infectious as witnessed by the fact that if you look at children under 15 living in a house with someone who has active TB, only 20 percent are infected," said Dr. George Comstock, an epidemiologist with the Johns Hopkins School of Medicine.
"This doesn't mean the risk is zero [aboard a plane], but over a relatively short period of time, it is not great."
In the United States, tuberculosis was a major killer of children and adults through the early 20th century. The advent of antibiotics in the 1950s caused the incidence to plummet, although the disease remained a problem in other parts of the world.
Recently it has resurged in urban areas. About 25,000 cases are diagnosed annually in the United States.
In New York, Newark and several other major cities, the failure of TB patients to take their medications has spawned vicious strains that are resistant to several drugs. In Baltimore, public health efforts have been credited with keeping the rate of drug-resistant cases low.
Strains that are resistant to the two mainline drugs -- isoniazid and rifampin -- plus any other antibiotics used against tuberculosis are considered particularly dangerous and difficult to treat.
The woman died from a strain that was resistant to isoniazid and a less commonly used drug, streptomycin. Ms. Bur said she could have been effectively treated with rifampin and other medications.
"It means we still would have had an effective drug to prevent future development of the disease," Ms. Bur said.
The case marks the fifth time in the past several years the CDC has investigated the possibility of TB transmission from a sick passenger to others aboard a plane. The agency has found no evidence that any passengers became infected in this fashion, although a sick flight attendant aboard one flight apparently did infect two other attendants.
The attendants had spent many hours together in the air and on the ground, the CDC said.
In recent years, the issue of cabin air quality has become controversial as airlines have been recirculating half the cabin air instead of pumping fresh air into the aircraft and exhausting stale air.
Flight attendants have complained that the new practice, which saves the airlines money, was causing health problems such as headaches and nausea.
Mr. Hopkins, the United spokesman, said he did not know whether the two planes involved in the May 11 flights were equipped with the new circulation system.
About half the seats on the 7 million domestic flights last year were on aircraft with the new circulation system.
In May, the Association of Flight Attendants was among several groups that complained to a House aviation subcommittee about cabin air quality.
"We urged more fresh air in planes and part of that reason was to reduce the proliferation of contaminants like tuberculin," Chris Witkowski, director of air safety and health with the 33,000-member flight attendants union.