The flu sweeping through Indiana is the worst in at least 20 years, but there may be signs that the worst is over — at least in Marion County.

More than 10 percent of Hoosiers who visited doctors’ offices and emergency rooms last week reported influenza-like symptoms, state health officials said Thursday.

Three deaths in the state last week were due to the H1N1 virus, the dominant strain infecting Hoosiers. Since June, H1N1 has claimed the lives of 10 Hoosiers.

Nearly 13 percent of all people visiting the state’s emergency rooms came because of flu symptoms, said Pamela Pontones, acting state epidemiologist. In the four years that the state has monitored emergency rooms, influenza symptoms never have accounted for so many visits.

“We are now experiencing a historical high,” said State Health Commissioner Dr. Judith Monroe. “How historic will this become? We don’t know. We don’t know if it will taper off.”

Thirty-nine schools last week reported absenteeism rates of 20 percent or higher, another barometer the state uses to monitor disease activity.

Most of the nation is seeing similar patterns. Health officials say the virus is widespread in 46 states.

Still, not all the news is grim.

The vast majority of those sickened by H1N1, also called swine flu, have had only mild cases. Each year, the seasonal flu causes about 700 to 800 deaths in Indiana; H1N1 has been much less deadly, especially considering the number of people who have contracted the illness.

And in Marion County, there are signs the outbreak may be slacking off — or taking a break.

Last week, Marion County saw a “substantial decrease” in the number of patients visiting local emergency rooms with flu-like illness, said John Althardt, spokesman for the Marion County Health Department.

Wishard Health Services also has noted a change in flu activity. While there are many more cases than typical for this time of year, this week there have been fewer flu patients, said Michelle O’Keefe, hospital spokeswoman.

Health officials are “cautiously optimistic” that the outbreak may be lessening, Althardt said.

Two weeks ago, three doctors at St. Francis Pediatrics Associates of Greenwood saw 190 young patients in one day. This week has not been as busy.

“Last week was awful,” said Dr. Kate McIntire, a doctor with the practice. “We just got off of fall break. We were hoping that when the kids were home and got away from each other, we might notice a difference.”

Still, concerns remain. Production delays have slowed shipments of the H1N1 flu vaccine, making it difficult for those in high-priority groups to find it. As of Thursday, Indiana had ordered 479,500 vaccine doses. State health officials originally expected to have more than 900,000 doses by mid-October.

The Marion County Health Department has received a new shipment of 5,500 vaccine doses, Althardt said.

The department plans to schedule a second vaccination clinic next week at Lafayette Square Mall.