Anne Schuchat, a physician at the Centers for Disease Control and Prevention, said the national trend was "worrisome" but not unexpected.
"In previous pandemics, there has been an increase in pneumococcal infections in younger people," she said.
The illnesses are caused by Streptococcus pneumoniae, a microbe often carried in the nose and throat. While often benign, the bacterium can cause bloodstream infections, fatal pneumonia and meningitis.
The clearest sign of the marked rise is coming from the Denver area, which usually records about 20 cases of "invasive pneumococcal disease" each October. This year, it has had 58, Schuchat said in a briefing for reporters.
Most invasive pneumococcal infections normally occur in the elderly, but in the Denver cases 62 percent were in people age 20 to 59, Schuchat said. Serious cases of influenza are also primarily hitting younger age groups.
When flu causes pneumonia, it can damage cells deep in the lungs, opening a portal for bacteria. In an analysis of about 75 fatal H1N1 cases earlier this year, autopsies showed that about one-third had bacterial pneumonia.
Pneumococcal infections are largely preventable with a vaccine that is given once or twice depending on a person's age. It is recommended for smokers and for people with asthma, kidney or liver problems, heart disease and other chronic ailments. Only about one-quarter of people with those conditions, however, have been vaccinated.
CDC officials have urged physicians in recent months to offer the vaccine to patients who qualify for it. Schuchat urged patients Wednesday to seek it out, adding she had been assured by the vaccine's manufacturers there is enough of it to go around.
"I strongly urge people to sort out whether you're in one of those high-risk groups and talk to your doctor or ask your pharmacist whether you can be vaccinated," she said.
Schuchat also addressed during the briefing the CDC's monitoring of severe reactions to the H1N1 vaccine. The agency's reports thus far have been "extremely reassuring," she said, with the pattern and severity of problems "pretty much what we see for seasonal flu vaccines." About 94 percent of reactions reported to the government are classified as "not serious," with soreness at the injection site the most common.
In particular, there has been no increase in Guillain-Barré syndrome, a rare, usually reversible form of paralysis. That condition rose slightly during an emergency vaccination campaign in 1976, after a strain of swine influenza, different from this year's H1N1, was detected among troops at Fort Dix, in New Jersey. That outbreak did not spread to the civilian population.
CDC is investigating 10 proved or suspected cases of Guillain-Barré syndrome among people who have gotten the vaccine, which is no more than would normally be expected in that number of people. About 80 to 160 cases of the condition occur each week in the United States, usually after an infection.
Have you noticed any article always reverts to the Swine Flu vaccine and how safe it is! The facts are proven they are ignoring the fatalities from the vaccine and most of the serious side effects, as they say there is no connection. I also find it interesting they are saying the bacterial pneumonia is from a Virus! That the Swine flu is causing those deaths. Those facts are not correct either - we already know there is something Much more happening than the Swine flu.