Atlanta ? The number of Americans infected by the AIDS virus each year is much higher than the government has been estimating, U.S. health officials reported, acknowledging that their numbers have understated the level of the epidemic.

The country had roughly 56,300 new HIV infections in 2006 – a dramatic increase from the 40,000 annual estimate used for the past dozen years. The new figure is due to a better blood test and new statistical methods, and not a worsening of the epidemic, officials said.

But it likely will refocus U.S. attention from the effect of AIDS overseas to what the disease is doing to this country, said public health researchers and officials.

“This is the biggest news for public health and HIV/AIDS that we’ve had in a while,” said Julie Scofield, executive director of the National Alliance of State and Territorial AIDS Directors.

Experts in the field, advocates and a former surgeon general called for more aggressive testing and other prevention efforts, noting that spending on preventing HIV has been flat for seven years.

The revised estimate by the Centers for Disease Control and Prevention and the methodology behind it were to be presented today, the opening day of the international AIDS conference in Mexico City.

Since AIDS surfaced in 1981, health officials have struggled to estimate how many people are infected each year. It can take a decade or more for an infection to cause symptoms and illness.

One expert likened the new estimate to adding a good speedometer to a car. Scientists had a good general idea of where the epidemic was going; this provides a better understanding of how fast it’s moving right now.

“This puts a key part of the dashboard in place,” said the expert, David Holtgrave of Johns Hopkins University.

Judging by the new calculations, officials believe annual HIV infections have been hovering around 55,000 for several years.

“This is the most reliable estimate we’ve had since the beginning of the epidemic,” said Dr. Julie Gerberding, the CDC’s director. She said other countries may adopt the agency’s methodology.

According to current estimates, about 1.1 million Americans are living with AIDS. Officials plan to update that number with the new calculations but don’t think it will change dramatically, a CDC spokeswoman said.