The Supreme Court Thursday erased any notion that the Americans with Disabilities Act was designed merely to help the wheelchair-bound navigate sidewalks or ensure that the disabled may continue to work. In ruling largely in favor of an HIV-infected patient and against Bangor dentist Randon Bragdon, the court properly found that human immunodeficiency virus, even as in this case when the carrier displays no outward symptoms, is a debilitating condition covered by the ADA.

What was left uncertain, however, is how far the ADA stretches to cover other asymptomatic illnesses. The uncertainty is likely to bring mischief in the future.

In September 1994, Dr. Bragdon told Sidney Abbott that because she was HIV positive, he would not treat her at his office but would fill a cavity in her tooth at a local hospital. Safety conditions, presumably, would be greater at a hospital. Ms. Abbott would be expected to pick up the added hospital cost of her care. Instead, she sued successfully under ADA.

The court had a couple of decisions to make in this case, but passed one back to the lower court: Did Dr. Bragdon use reasonable judgment when he referred Ms. Abbott to the hospital? That question already has been answered by the doctor’s own medical organization, the American Dental Association, the Centers for Disease Control and the doctor’s peers in Maine. The use of universal precautions — which assume that all patients carry infectious diseases because a dentist cannot know otherwise — is an acceptable way to treat a patient who is HIV positive.

What the justices did decide was whether HIV was a disability, defined to include a “physical or mental impairment that substantially limits one or more of the major life activities of such individual.” Some of the examples of these activities given under the act were caring for oneself, performing manual tasks and walking. The court, considering with some detail the “immediacy with which the virus begins to damage the infected person’s white blood cells and the severity of the disease,” even in asymptomatic cases, held that HIV infection meets the definitions of impairment from the moment of infection.

It further referred to a 1988 opinion from the Department of Justice, which concluded that the Rehabilitation Act, later adopted into ADA, “protects symptomatic and asymptomatic HIV-infected individuals against discrimination in any covered program.” So far, so good. The court found that people with HIV were disabled by a pervasive and deadly disease and deserved protection under the act.

Then things get interesting.

To fully meet ADA requirements, Ms. Abbott had to show that a major life activity was substantially limited. She argued that the major life activity affected by HIV was her decision not to bear children because of concerns that the child might become infected. Is the choice not to reproduce the loss of a major life activity? The court, 5 to 4, said yes.

In dissenting, Chief Justice William Rehnquist concluded that Ms. Abbott’s argument “taken to its logical extreme, would render every individual with a genetic marker for some debilitating disease `disabled’ here and now because of some possible future effects.” His point is an appropriate warning to Congress to consider limits for what largely has been a valuable law.

For instance, if HIV prevents the bearing of children and so qualifies under ADA, does impotence also qualify? What about a fear of passing along a predisposition for alcoholism? If an asymptomatic illness is protected, can a manic depressive sue under ADA after being denied a job? How broadly to interpret the court’s decision is important both to the ADA and the National Fair Housing Act Amendments, which uses the same definitions of disability to ban housing discrimination.

The political and emotional turmoil around HIV makes decisions about the people infected with it particularly difficult — and makes protecting these people particularly important. Dr. Bragdon should have treated Ms. Abbott at his office. It would have been both the ethically proper thing to do and, according to a variety of trustworthy sources, an acceptably safe thing to do.

Where the decision on child-bearing leads the nation is anyone’s guess, but expect mischief ahead.