Federal officials said Wednesday that they have noticed “a worrisome spike in serious pneumococcal disease” linked to infections with pandemic H1N1 influenza. Health authorities normally see an increase in such infections associated with seasonal flu, but this year the rate is substantially higher than normal and striking younger people rather than the elderly, according to Dr. Anne Schuchat, director of the Centers for Disease Control and Prevention’s National Center for Immunization and Respiratory Diseases.

And for the second week in a row, the American College Health Association has reported a drop in influenza-like illnesses on college campuses, a 37 percent decrease for the week ending Nov. 20, following a 27 percent decrease the preceding week. Those data suggest that the first wave of swine flu has passed its peak.

The pneumococcal infections typically occur when an influenza infection weakens the lining of the lungs, allowing bacteria that normally reside in the nose and throat to make their way down to the lungs, where they cause severe disease, inflaming the lungs and often spreading through the blood to other organs.

Most of the pneumococcal infections can be prevented with a vaccine called Pneumovax that is recommended for people with medical conditions that leave them at high risk, but only about a quarter of such people have received an immunization.

The problem with pneumococcal infections is showing up in the CDC’s Active Bacterial Core surveillance program, which monitors infections at 10 sites. In the Denver metropolitan area, there are typically about 20 such infections in October. This year, there were 58, most of them among people under the age of 60, according to the ABC surveillance.

“We don’t think this is the only area of the country where this is going on,” Schuchat said. “There is some evidence of an increase at multiple sites, but there is probably more timely reporting in Denver.”

Schuchat said 61.2 million doses of swine flu vaccine are available for ordering by the states as of Wednesday, an increase of more than 7 million doses since last week.

“We’re expecting to see vaccination efforts really step up as we head into December,” she said.

The agency also reported its first assessment of potential side effects from vaccinations.

“A lot of people have been waiting for this report, and we think it is good news,” Schuchat said. “The patterns we are seeing are pretty much exactly what we see with seasonal flu.”

There have been 10 reports of Guillain-Barre Syndrome that are being investigated. That syndrome is a particular concern because there were reports of an increase in incidence following a 1957 swine flu vaccination program.

“The number of reports, given the number of doses (of swine flu vaccine given), is not at all notable,” Schuchat said. “It’s important to remember that Guillain-Barre Syndrome happens, with or without the vaccine. Every week, 80 to 160 people come down with it.”