The state AIDS Administration now estimates that between 16,000 to 30,000 Marylanders were infected with the AIDS-causing human immunodeficiency virus at the end of 1990.
The new estimate is far lower than the previous one of 70,000.
AIDS Administration officials agreed yesterday that the revised estimate represents a "significant decrease" in numbers, but urged the public not to be lulled into thinking the magnitude of the state's AIDS problem has diminished.
"No, we don't need to do less, we need to do more," said Dr. Kathleen F. Edwards, the AIDS Administration director. "AIDS is still a major health problem. We still have no vaccine, we still have no cure.
"And, this will in no way lessen my funding requests from the federal government and state legislature to deal with AIDS in Maryland."
Edwards, however, refused to say how much money she is seeking. Last year, the state pumped $4.5 million into the battle against acquired immune deficiency syndrome while the federal government provided $7.8 million.
Dr. Joseph Horman, the AIDS Administration assistant director for prevention and epidemiology, said, "There's no way anybody can be complacent. We still have a very significant problem in Maryland.
"At least half of those estimated to be infected don't know they are infected and could be spreading the disease. And, we have a job to do with those who are infected. They're not always practicing safe sex."
The new estimates are being made public to give people a "more realistic picture" of the epidemic, said Dr. Audrey Rogers, the AIDS Administration's chief of epidemiology.
The officials also noted that estimating the epidemic is an inexact science and that the figures could rise again.
The national estimate on HIV infection, coming from the federal Centers for Disease Control in Atlanta, also has been revised downward to show that an estimated 500,000 to 1 million instead of 1 1/2 million Americans could have been infected in 1990.
Since the epidemic started in 1981, Maryland's total number of AIDS cases has reached about 3,200, and, of those, more than 2,000 people have died. Nationally, about 160,000 Americans have been afflicted with the disease that cripples the immune system and, of those, more than 100,000 are dead.
The most conservative revised HIV infection estimates have been produced through a computer model by Dr. Ivan Kramer, an assistant professor of physics at the University of Maryland Baltimore County.
"We now have more data. We've watched this longer," explained Rogers.
"Studies in San Francisco, at Johns Hopkins and in Hershey, Pa., have confirmed that the average incubation period of HIV infection is 11 years," Rogers said. "Last August, through a state health department survey, we learned that four per 1,000 childbearing women in Maryland were HIV-infected. That means that 300 infected women are giving birth each year."
According to Kramer, the new incubation data show that after 11 years, 53 percent of those infected come down with AIDS, while 47 percent are walking around with no obvious symptoms.
His estimate on the extent of HIV infection in the state has been tempered, he said, by "what we don't know will happen to the rest." In the past, the assumption has been that after 22 years, everyone infected would develop AIDS, Kramer said.
The discrepancy between the past and most recent estimates was also due to the use of a formula that the CDC has since abandoned, the state AIDS experts said.
The model, which includes factors such as the degree of infectiousness, the contacts between individuals and numbers of people susceptible to infection, also depends upon the accuracy of the numbers of reported cases, among other things. Exact information is not available for many of these factors, and this could skew the case projections, the state officials said.
Edwards said that while the computer model is based on actual numbers of AIDS cases reported to the health department, it probably underestimates the true number of HIV-infected people in the state.
"Maryland physicians frequently fail to report cases and, occasionally, while women die as a result of HIV infection, the illnesses they develop do not meet the AIDS case definition, leaving them uncounted as cases," she said.
The beauty of the mathematical model, only one of several methods used to calculate the size of the epidemic, is that it can be used to project future numbers, which are needed for budgetary planning, the officials said.
The other primary method, which has shown that as many as 30,000 Marylanders may be infected, generalizes from recently available data obtained by testing anonymous blood samples for the HIV antibody, which indicates infection.