TUESDAY, Dec. 20 (HealthDay News) -- Severe sepsis can impair the immune system, a new study says.

Sepsis causes more than 225,000 deaths annually in the United States, the researchers said. "Developing new therapies for sepsis has been particularly challenging, with more than 25 unsuccessful drug trials," Jonathan S. Boomer, of the Washington University School of Medicine, St. Louis, and colleagues wrote as background information in the study. "Characterized by an initial intense inflammatory response or 'cytokine storm,' patients with sepsis may present with fever, shock, altered mental status, and organ dysfunction," they said.

"Whether this hyperinflammatory phase is followed by immunosuppression is controversial. Animal studies suggest that multiple immune defects occur in sepsis, but data from humans remain conflicting," the researchers noted.

Sepsis is a severe, systemic bacterial infection occurring in the body's blood system or tissues. It can be life-threatening, and patients require rapid treatment with intravenous antibiotics.

For the new study, researchers analyzed lung and spleen tissue from 40 intensive care unit patients, average age 72, who died with active severe sepsis and compared them to spleen and lung samples from a control group of 49 people, average age 53, who died without sepsis.

The median (midpoint) number of days in the ICU for patients with sepsis was 8, and the median duration of sepsis was 4 days.

Findings from biochemical tests and cell and tissue analyses for patients who died of sepsis were consistent with immune suppression, compared to the patients who did not have sepsis when they died.

The study appears Dec. 21 in the Journal of the American Medical Association.

With therapies improving, patients are more likely to survive sepsis, the researchers suggested, but may still have impaired immune systems, leaving them more susceptible to infections from organisms that wouldn't affect healthier people.

"The present study has a number of important therapeutic implications. Most investigative agents in sepsis have been directed at blocking inflammation and immune activation. Although such therapies may be successful if applied early, they may be harmful if applied later in the immuno-suppressive phase," the researchers wrote in a journal news release.

"An important part of implementing more targeted therapies will be to accurately determine the immune status of individual patients during their disease," the researchers concluded.

More information

The U.S. National Institute of General Medical Sciences has more about sepsis.