MONDAY, June 27 (HealthDay News) -- Certain groups of patients treated at hospitals in U.S. territories have poorer outcomes and higher death rates than those treated at hospitals in U.S. states, according to a new study.

Nearly five million people live in U.S. territories, which include Puerto Rico, Guam, American Samoa, the Northern Mariana Islands and the U.S. Virgin Islands, according to background information in the study.

Researchers looked at outcomes and death rates for Medicare fee-for-service patients with heart attack, heart failure or pneumonia who were treated at 57 territorial hospitals and about 4,800 stateside hospitals between July 2005 and June 2008.

The territorial hospitals had worse performance in treating all three conditions and had higher death rates. Compared to stateside hospitals, territorial hospitals had about two additional deaths for every 100 heart attack patients, one additional death for every 100 heart failure patients, and three additional deaths for every 100 pneumonia patients.

"Despite the national effort to address health-care disparities through increased public reporting and standardizing hospital performance, hospitals in the U.S. territories have been largely neglected," concluded Dr. Marcella Nunez-Smith, of Yale University School of Medicine, and colleagues.

The study appears June 27 online in the journal Archives of Internal Medicine.

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