America's two swine flu deaths — a toddler and a pregnant woman — each suffered from several other illnesses when they were infected with the virus, according to a study released Thursday.

The report by the Centers for Disease Control and Prevention presented a clearer picture of the complicated medical situations faced by those who have gotten swine flu and had the most serious cases so far.

The Mexican toddler had a chronic muscle weakness called myasthenia gravis, a heart defect, a swallowing problem and lack of oxygen. Little Miguel Tejada Vazquez fell ill and died during a family visit to Texas.

The pregnant woman, Judy Trunnell, 33, was hospitalized for two weeks until she died Tuesday. The teacher was in a coma, and her baby girl was delivered by cesarean section. According to the report, she had asthma, rheumatoid arthritis, a skin condition called psoriasis and was 35 weeks pregnant.

People with chronic illnesses are at greatest risk for severe illness from the flu, along with the elderly and young children. So far, most of those with the swine flu in the U.S. and Mexico have been young adults.

"We're still learning about what patients are most at risk" from the new virus, said Dr. Fatima Dawood, a CDC epidemiologist.

The CDC report released by the New England Journal of Medicine also provided more detailed information on 22 people hospitalized with swine flu. Nine had chronic medical conditions, including the two who died and a 25-year-old man with Down syndrome and a congenital heart disease. Five of the patients had asthma alone.

Separately, the CDC also described the symptoms experienced by Americans with swine flu. About 90 percent reported fever, 84 percent reported cough and 61 percent reported a sore throat — all similar to what's seen with seasonal flu.

But about one in four cases have also involved either vomiting or diarrhea, which is not typical for the normal flu bug.

It's possible the virus is spreading not only through coughed and sneezed droplets — as with seasonal flu — but also through feces-contaminated hands, said Dawood.

"This is a new virus and we're still learning how transmission occurs," she said.

There are now nearly 900 confirmed cases in the United States, said the CDC's acting chief, Dr. Richard Besser. That count included 42 hospitalizations as of Thursday.

About 10 percent of the Americans who got swine flu had traveled to Mexico and likely picked up the infection there. That's a change from over the weekend when the CDC said about a third of the U.S. cases at that point were people who had been to Mexico, where the outbreak began.

The ongoing spread within the U.S. borders explains why a shrinking proportion of cases are people who traveled to Mexico, Besser said.

The ages of those in the U.S. who got swine flu now range from 1 month to 87. More than half are under 18.

In the new report, CDC scientists discussed what's known about the swine flu virus. It has a unique combination of genes from flu viruses seen in birds, humans and pigs from not only North America but also Europe and Asia.

"There are no really close relatives, nothing we can say was an immediate precursor," said Michael Shaw, a CDC microbiologist.

It's still not clear how the combination occurred. Pigs from the Americas are imported into Europe and Asia for breeding purposes, but not the other way around, CDC officials said. Yet the virus first surfaced in California and Mexico.