Deaths From Mystery Illness Increase to 11 : Disease: Officials find no new cases but say earlier one matches criteria. Researchers seek a cause of outbreak that has struck Arizona and New Mexico.

New Mexico authorities said Monday that they have observed no new cases in the last 24 hours of the mystery illness that has brought fear to the Four Corners area of northern Arizona and New Mexico.

But the death toll from the flu-like disease has risen to 11 as researchers have ferreted out an earlier case that matches criteria established for the disorder, now known as unexplained respiratory distress syndrome, or URDS.

Researchers from New Mexico and the U.S. Centers for Disease Control and Prevention in Atlanta are mystified about the cause of URDS, having ruled out the most common infectious agents, but the most likely explanation is an undiscovered virus. Intriguingly, all the victims have been young, apparently healthy people between ages 13 and 31. Most infectious agents, in contrast, strike infants and the old or infirm.

As many as 50 laboratory workers here and in Atlanta are feverishly attempting to isolate an infectious agent or antibodies from patients and are trying to induce the disease in laboratory animals by injecting tissue samples or blood from victims. But researchers concede that it could be months before the cause is identified.

Perhaps as many as 150 others are trying to identify a common food, environmental agent or other factor that links the victims, who come from scattered locations in the area. The only common factor identified so far is that the bulk of victims have been Navajos and all victims have lived on or near the 24,000-square-mile reservation here, the country’s largest.

The only bright spot, said Dr. Frederick Koster of University Hospital here, is that “the survival rate is decent if people get to the hospital early enough.”

“At least we can give better advice to people now than we could last week,” said Ron Wood of the Indian Health Service.

According to their refined description of URDS developed Monday, the early symptoms are fever, muscle aches and either cough, conjunctivitis (redness of the eyes) or headache. Fevers approach 103 degrees Fahrenheit and the muscle aches strike primarily the legs, hips and lower back.

“It feels like you just ran a marathon,” Koster said. Although those symptoms sound like influenza, the victims do not have rash, runny nose and swollen lymph glands characteristic of flu.

Public health authorities recommended that anyone with those symptoms in the Four Corners area visit their physician or a hospital.

As the disease progresses, patients develop an accumulation of fluid in their lungs that effectively suffocates them. That progression can take as short a time as a few hours or as long as four days.

In addition to the 11 victims who died, the state Health Department has identified seven others who have or had the syndrome, five who may possibly have the syndrome and four in whom the diagnosis is questionable, said Dr. Ron Voorhees, deputy state epidemiologist. Of the 18 definite cases, 12 are American Indian, five are Anglo and one is Latino. Eight are female and 10 are male. Fourteen cases have been identified in New Mexico and four in Arizona.

Treatment has involved forced ventilation of the lungs to help patients breathe and a broad spectrum of intravenous antibiotics to kill any bacteria that might be present. But Koster conceded that physicians do not know which actions have helped the patients.

So far, researchers know that URDS is not linked to AIDS, sexual transmission or any of the most common bacteria and fungi. They also have ruled out toxins such as anthrax and rare organisms such as legionella, which caused an outbreak of Legionnaires’ disease in 1976 and 1977.

Victims often have a low platelet count or a high white blood cell count, consistent with an infectious agent, but the overall pattern of the disease “is different from anything I’ve ever seen,” said Koster, an infectious disease specialist at University Hospital and the University of New Mexico who has treated 11 victims. An isolated intensive care ward for URDS patients has been established at the hospital, which is housing three victims. Two are in critical but improving condition and one is satisfactory, Koster said. Patients from throughout the state will be transferred there when lung complications set in.

Researchers agree that the agent is not highly contagious or there would be a much higher number of cases. That is supported by the fact that no health care workers have developed the syndrome. But prolonged contact may cause infection, physicians cautioned.

Two deaths involved a couple who were engaged to be married, and those deaths alerted authorities to the problem. Henry Henio Jr., 24, of Pine Hill, Ariz., a forest firefighter, became ill last week on the way home from the funeral of his fiancee, Irene Irish Beaver, 24, and died shortly thereafter. He was considered very healthy, as was Beaver.

Further investigation revealed one case of the syndrome in March, a handful in April and the rest in May, suggesting that the disease is spreading. Researchers have uncovered three possible cases in Humboldt County in Northern California that occurred this winter, and an unknown number that may have occurred in Virginia in 1990.