WASHINGTON — Think you have the flu? In some places, you can now go directly to the Internet and report your symptoms to officials eager to spot outbreaks.

Say you feel sick, but before you see a doctor you search the Web for information, or blog or Twitter about the flu. Your worries will be detected by companies prowling the Internet for disease trends.

If you actually come down with the flu, and the doctors want to know who you’ve been in physical contact with, your trusty cellphone could soon tell them.

And someday, scientists hope, this “infodemiology” might help forecast and track a flu epidemic the way experts monitor the weather.

As health officials gear up for the flu season amid the global H1N1 pandemic, technology and new forms of Internet social interaction are transforming how such outbreaks are monitored.

“All these things really change the way that we can manage diseases,” said Alessandro Vespignani, professor of informatics at Indiana University. “It’s not just … a passive approach, where we just wait for the disease and then try to do something.”

Currently, most disease tracking is done through doctors reporting cases of illness they have seen. It’s a reliable system but often involves a lag time of a week or more in reporting and does not account for people who don’t go to the doctor.

Internet surveillance raises questions about privacy and confidentiality. But experts say it has the advantage of speed and can augment the current system by detecting sick people who might not see a doctor.

Google’s public Flu Trends system, for example, is designed to pick up early clues by tracking and analyzing Internet searches for flu information. “We keep track of what queries have been asked, and how often,” said Roni Zeiger, the Flu Trends product manager. Because people often search for information on the Web before going to a doctor, the system can provide an early warning of trouble, he said.

During the 2007-08 flu season Google used an early version of the system that consistently detected flu rates one to two weeks ahead of official reports, the company said in a paper published in February.

Other companies and programs scan live Web chatter for mentions of, or reports about, the flu.

Boston-based HealthMap’s automated system sends out an hourly Web “crawler” that hunts for flu information in seven languages.

Its creators on Tuesday launched a cellphone application called “Outbreaks Near Me” that can alert users to illnesses nearby. “If you move into a zone where there’s an outbreak, your phone would actually alert you,” said John Brownstein, assistant professor of pediatrics at Children’s Hospital in Boston, where HealthMap is based. The application also allows users to send back to HealthMap their own flu alerts.

Maryland has launched a “flu watcher” program in which volunteers report their health conditions weekly via the Internet. Project officials say the state is the first in the country to have such a system: the Maryland Resident Influenza Tracking Survey.

“We get people to sign up online and give us their e-mail address,” said Rene Najera, an epidemiologist with the Maryland Department of Health and Mental Hygiene. “They give us their county of residence, their month and year of birth. We don’t get too personal with them. We just want some basic demographics.

“Every week … we send them a survey … ‘Did you have any fever? Did you have any cough? Did you have any sore throat in the week previous?’” he said. If the answer is yes, more detailed questions are asked. So far, 740 people across the state have signed up.

Najera said that on Tuesday Maryland expanded the system to allow participants to report other members of their households as well as themselves.

Several countries have similar projects.

“Every Monday, we get a response back from just over 6,000 people,” Craig Dalton, who oversees Australia’s Flutracking project, said via e-mail. “About 3,000 responses come in within the first 6 hours.”

There are also programs in Italy, the Netherlands, Britain and other countries, Vespignani said, with tens of thousands of volunteers.

In Singapore, scientists have gone a step further, testing a system called FluLog that could use Bluetooth cellphone technology to locate people who had been in proximity to someone who has become infected.

It’s a high-tech version of a process called “contact tracing,” said Mehul Motani of the National University of Singapore’s Faculty of Engineering. Typically, he said “when you have a suspected case, you interview the suspected case, and you ask them: ‘Where have you been? … Who have you been in sustained contact with?’ “ The idea is to locate others who might get sick.

FluLog would augment the process with the Bluetooth identification technology. “If you and I happened to be in a meeting, your cellphone and my cellphone would discover each other, and then this information would be logged, (and) stored in a secure central database,” he said. “Then if you or I became a suspected case, we could easily mine this database and figure out who are the potential people who are at risk.”

Motani said the system would be voluntary: “You would go to a Web site and register yourself,” then be e-mailed if you had been exposed to the flu.

At Indiana, Vespignani has tried modeling an outbreak, the way forecasters model a hurricane. “It’s like doing weather forecasts in which you try to get all the initial conditions, and then you run your numerical models on the computer to try to anticipate what will be the evolution.”

The problem is that disease spreads in a fluid social system much more complex than the atmosphere, he said, so “these systems are much more difficult to track than weather.”

None of these tools, experts reiterate, can replace the kind of in-depth disease surveillance and testing performed by city, state and federal agencies such as the U.S. Centers for Disease Control and Prevention.

“You’re always going to have to have this verified against a system that’s physician-based,” said Ashley Fowlkes, an epidemiologist with the CDC. “It’ll always be a nice adjunct to current surveillance systems and … may serve as an early warning system.”

The CDC currently has a network of 2,500 doctors nationwide that reports flulike illness on a daily or weekly basis, she said. And the CDC issues a weekly public report on the Internet called Fluview.

Despite the advantages of Internet-based surveillance systems, they also raise issues of privacy.

“The Internet has been … a major scientific revolution,” Vespignani said. With “all huge scientific revolutions there are enormous potential dangers. And confidentiality, privacy, is probably the first major issue at stake here.”

“This is like nuclear power,” he said. “You can do atomic bombs with it … or you can do nuclear medicine and target cancers.”