May 1996
ALLENTOWN, Pa. — City health officials here began testing 1,432 children and up to 2,000 adults for Mycobacterium tuberculosis infection because they may have been exposed to the bacterium by a pediatrician with infectious tuberculosis.
Although health officials have identified people infected with tuberculosis, they have found no evidence that the pediatrician was the source, and they have not detected any child with active TB, said Barbara Stader, director of the Allentown Health Bureau. Because of possible exposure, however, 228 children younger than 2 years have been placed on rifampin as a precaution, Stader said.
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People were possibly exposed to tuberculosis from November through the middle of February at a hospital where the pediatrician worked, Stader said. At press time, 51 people have tested positive, including 12 children younger than 18 years of age. Some people who have tested positive have risk factors for tuberculosis, such as having been born in a country with a high rate of TB.
Although the pediatrician had coughing fits, he wore no mask because he believed that the coughing was related to reactive airway disease and not to tuberculosis, she said. The pediatrician saw patients in the newborn nursery, the inpatient ward and in an outpatient pediatric clinic. "That is why we have so many potentially exposed children," Stader said.
Moreover, the pediatrician's tuberculous strain was resistant to isoniazid, which is why the children were placed on rifampin. "The worst-case scenario happened here," Stader said.
The state has suspended the pediatrician's license because he failed to take measures to prevent exposure to others after being told he had infectious tuberculosis, Stader said.
Children who are 1 to 2 years old will be taken off rifampin if they test negative for M. tuberculosis three months after the suspected exposure, Stader said. Health officials have asked parents to keep potentially exposed children on rifampin for nine months if those children are age 1 year or younger.
Health officials plan to test people twice. The first test is to establish baseline prevalence of infection and the second, which will be conducted three months after the first, is to identify new infections, Stader said.
Once infected, it takes one to three months for a person to test positive for M. tuberculosis said Jeffrey Starke, MD, professor of pediatrics at Baylor College of Medicine, Houston, and a specialist in pediatric tuberculosis.
Exposure to somebody with active tuberculosis does not ensure transmission of M. tuberculosis, Starke explained. Transmission depends on such factors as the infectiousness of the person with tuberculosis, the air ventilation where exposure occurred, and the vulnerability of the person exposed.
An approach that health officials use to gauge the infectiousness of a person with TB is to determine if the person's sputum contains M. tuberculosis and to test the person's closest contacts, such as family members and co-workers. If these people are free of tuberculosis infection, the person with TB may not be particularly infectious, according to Starke. Health officials in Allentown had not completed their investigation of the pediatrician's contacts at press time.
As people age, their risk of developing active tuberculosis following infection with M. tuberculosis decreases. Thus, the younger a child is, the more likely the child will develop active TB following infection with the tuberculosis bacterium, Starke stated. Researchers have estimated that up to 40% of children under age 1 who become infected and do not receive treatment will develop disease in one to two years.
In studies done in 1952 prior to the discovery of isoniazid, among children under age 3 years, 16% of black children and 8% of white children who were infected with M. tuberculosis but did not receive treatment died from tuberculosis. By comparison, the average healthy adult who is infected and does not receive treatment has a 5% to 10% lifetime risk of developing disease.
Because active tuberculosis is more likely to develop in young children after infection with the TB bacterium, Starke said he believes that Allentown officials have taken the right precaution by placing children on rifampin.
"They [health officials] do not know who really has been exposed and who has not, so they are trying to take the safest track," said Starke, who chairs the Advisory Council for the Elimination of TB, which advises the Centers for Disease Control and Prevention.
In situations such as that in Allentown, physicians in the community must work with public health officials when deciding how to care for a particular patient, Starke said. "What you are going to do with a child will depend to some extent on what the [test] results are for all the other children," he said.
Although it is important that physicians follow health department recommendations, "there is always room for individual exceptions," such as children who are highly susceptible to disease, Starke said. A child with cancer, for example, might require more aggressive treatment and longer treatment than a healthy child who had exactly the same TB exposure, he said.
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