U.S. health officials said on Wednesday they are seeing a worrying pattern of serious bacterial infections in swine flu patients, mostly among younger adults not normally vulnerable to them.

The pattern is typical of pandemics such as the current H1N1 pandemic but shows the need for patients and doctors to keep an eye out for the infections and treat them quickly, Dr. Anne Schuchat of the U.S. Centers for Disease Control and Prevention told reporters.

“We are seeing an increase of serious pneumococcal infections around the country,” Schuchat told a telephone briefing.

“That is the serious type of pneumococcal disease where the bacteria invades the blood and other internal sites.” These so-called secondary infections can follow infection with a virus such as flu and often are seen among people who die from influenza.

A close look in Denver showed 58 cases of serious Streptococcus pneumoniae infections in October, a month when usually about 20 cases are seen, Schuchat said. And while such infections normally affect people over 65, these were almost all among people under 60, she said.

“The findings in Denver probably reflect infections that are occurring in other parts of the country where surveillance hasn’t been as intensive,” Schuchat said.

Merck makes a vaccine called Pneumovax to protect adults against 23 strains of these streptococcal bacteria, which is recommended for adults with diabetes, asthma, cancer and other conditions, as well as smokers. But only about a quarter of adults who should get it ever do, Schuchat said.

Children are protected against seven strains of these bacteria with Pfizer Inc’s Prevnar.

Strep infections can be treated with antibiotics and the symptoms are often clear, Schuchat said.

“Having a high fever and cough and then feeling miserable and then feeling better and then suddenly taking a turn for the worse - that is a serious warning sign,” she said.

The U.S. government is trying to vaccinate as many as 160 million high-priority people but companies are having trouble making and packaging vaccine. As of Wednesday, Schuchat said 61.2 million doses of H1N1 vaccine had been used or were ready to order.

She said surveillance so far had shown the H1N1 vaccine was as safe as the seasonal flu vaccine

“We don’t see any problems at all,” Schuchat said. Ten cases of a rare neurological condition called Guillain Barre Syndrome have been reported among people who got vaccinated, which is no more than would be seen among people not vaccinated, she said.

“So far, the vaccine data suggests that this is a safe vaccine,” Schuchat said.

“We are expecting to see vaccination efforts really step up as we head into December,” Schuchat added.

The CDC estimates swine flu has infected at least 22 million Americans and killed 3,900.

The World Health Organization says the pandemic is moving from west to east and appears to have made one peak in the United States and the westernmost parts of Europe.

Globally, WHO estimates that 80 million doses of influenza vaccine have been distributed.

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* Bacterial infections show worrisome rise

* US now has 61.2 million swine flu vaccine doses

* No signals of vaccine safety problems

By Maggie Fox, Health and Science Editor

WASHINGTON (Reuters)