Two people have died and five others have been hospitalized in a mysterious cluster of respiratory illnesses in southeast Alabama, state health officials said.

The victims, all adults, had symptoms including fever, cough and shortness of breath, but the cause of the illnesses is unknown, said Dr. Mary McIntyre, the acting state epidemiologist for the Alabama Department of Public Health. The hospital is using respiratory precautions, which include requiring staff to wear special N95 masks that reduce the chance of infection.

State health officials have collected and analyzed samples of specimens from all patients. So far, one sample has tested positive for H1N1 influenza A, but it's not clear that that is behind the unusual illnesses. There's no evidence of other kinds of flu, including the H7N9 strain that has caused illness and death in China, McIntyre said.

Laboratory samples have been sent to the Centers for Disease Control and Prevention, but testing results are not yet available, officials said.

There's no evidence that any of the victims had a connection or traveled outside the country, which would have put them at risk for unusual pathogens, including a deadly new coronavirus recently christened MERS or Middle East Respiratory Syndrome.

"At this point it's too early to tell," McIntyre told NBC News. "That's why we called it a respiratory illness of unknown origin."

State and federal health officials will continue to investigate the illnesses.

Related: