This is the flu season. So it is also the season to be on the alert for Reye's syndrome, the too-often fatal confluence of symptoms that can ravage the vulnerable systems of children and adolescents, often leaving in its survivors a legacy of mental or physical impairment.

Over the past few years doctors have become increasingly aware of the presence of Reye's. They are also more adept at its early diagnosis -- when treatment is most likely to be successful -- and quicker to get Reye's victims to major centers which are uniquely equipped to handle its explosive physiological progress.

Its causes still are unknown, but recent studies have established a link between the incidence of Reye's syndrome and the use of medicines containing salicylates -- simple aspirin.

The relationship of aspirin and Reye's is circumstantial and no one is claiming that aspirin is the only cause, or even a single cause of Reye's syndrome. However, separate studies in Arizona, and later in Michigan and Ohio which had almost epidemic-occurrences of Reye's last winter, have indicated some relationship.

Aspirin-containing medicines, the studies found, were taken significantly more often during the viral illness that nearly always precedes the onset of Reye's by the children who got it, than it was among those in the control group -- children who had the same viral illness but who did not get Reye's.

The Center for Disease Control and the National Academy of Pediatrics are urging parents to be cautious about the use of aspirin. In addition, some doctors are reluctant to recommend that aspirin substitutes (like Tylenol) which contain acetaminaphen, should be indiscriminately used either, because of that drug's potential effect on the liver, an organ involved in Reye's.

The disorder usually strikes children and adolescents, from infancy to about 20 years and occcasionally older, following a viral illness such as a cold, flu or chicken pox. (There have been occasional cases, however, where apparently healthy youngsters have been stricken.)

Classically, the child will seem to be recovering but will suddenly begin to vomit relentlessly, perhaps run a fever, and seem lethargic and unresponsive or unusually fatigued or sleepy. As the illness progresses, behavioral changes, often bizarre, may occur. A normally agreeable child may become combative or may even hallucinate. In fact, up until a few short years ago, adolescents presenting these symptoms in hospital emergency rooms were too often treated as possible drug overdoses.

From there, the Reye's victims may sink into a coma and die without the intervention of an intensive pediatric-neurologic-surgical support team working until the crisis is past. The final, most devastating effect of Reye's is swelling of the brain, the immediate cause of most of the fatalities and residual problems in survivors.

When Reye's syndrome is suspected, the child should have an immediate blood test to determine the level of liver enzymes. The results must be gotten the same day. Elevated enzymes are the princial basis for early diagnosis. Even waiting overnight can be fatal.

Heightened awareness of Reye's and its early symptoms, doctors feel, had begun to work a lessening of its overall mortality rate from the terrifying 30 to 40 percent of a few years ago. Last year in the U.S. there were perhaps 450 cases of hospital-based Reye's syndrome, but because the disease is not required to be reported to the Center for Disease Control in Atlanta, the number of severe cases is probably greater and the number of mild cases, much, much greater.

Dr. Joel Taubin, a Washington internist who lost his 11-year-old son to Reye's three years ago, has made education about the syndrome one of his major avocations. He has urged federal legislation to increase research funds for the illness and to require that its incidence be reported to the Center for Disease Control in Atlanta.

Some states, such as Michigan and Ohio where it has seemed to cluster, report it voluntarily."

Meanwhile, the CDC is deeply concerned about Reye's syndrome, and recently published the results of the Michigan and Ohio tests indicating the aspirin connection, in its weekly report.

The neurological institute of the National Institutes of Health is sponsoring a national consensus conference on Rye's syndrome in March. Pediatricians, neurologists and epidemiologists will compare notes on identification and treatments and come up with guidelines for both parents and physicians.

Also, public television stations throughout the country are showing "Reye's Syndrome -- The Child Killer," an informational documentary on Reye's made before the aspirin studies were published. (In the D.C. area it will be broadcast in the next few weeks on Ch. 14/53, the Northern Virginia public TV station. It will be followed by a live call-in discussion with a panel of area experts.)

The Reye's foundation is updating a pamphlet which may be obtained from the Reye's Foundation, P.O. Box, RS, Benzonia, Mich. 49616. Or by writing Dr. Joel Taubin, Suite 504, 1145 19th St. NW, Washington, D.C. 20036. Dr. Taubin also is available to answer questions. Call him at 296-4002.