ATLANTA, OCT. 23 -- A bacterial infection that may be as serious as toxic-shock syndrome appears to be on the rise and is striking children as well as adults, researchers reported today.

New research points to significant changes in the pattern of severe streptococcal infections, Dr. Charles Hoge of the federal Centers for Disease Control reported at an American Society for Microbiology conference.

Streptococci are common microbes, familiar as the cause of strep throat. But in rare cases, they can cause extremely serious infections.

Three years ago, researchers began to talk of toxic-shock syndrome caused by streptococcal infections, not the staphylococcal bacteria implicated in the much-publicized illness linked to tampon use.

Now, researchers from the CDC and in Pima County, Ariz., have studied 128 cases of group-A streptococcal infections that occurred in the Tucson area between January 1985 and March 1990 to determine the prevalence of the most severe cases.

Fifty-four cases occurred from 1985 to 1987. None of those featured symptoms similar to those of toxic-shock syndrome: low blood pressure, rash, peeling skin, multi-organ involvement. But six of the 74 infections studied from 1988 to 1990 did. One of those six patients died.

Tests on the bacteria samples from Pima County found a propensity toward production of a specific toxin, which was present in at least two of the six toxic-shock-like cases. Toxic-shock syndrome is so named because its symptoms are caused by a toxin produced by the responsible bacteria.

While the study was limited to one county, the pattern is clear, Hoge said: Streptococcal toxic-shock syndrome was significantly more likely to occur after 1988. He and his colleagues reported that changes in strains of strep bacteria may be responsible for the increasing seriousness of strep infections.