Using contraceptive of any variety appears to partially protect women from developing toxic-shock syndrome, the rare and sometimes fatal disease associated with tampon use.

The effect of contraceptives was revealed in two separate studies of toxic-shock victims published in this weeks's New England Journal of Medicine. The studies found no link between the disease and frequency of sexual intercourse, intercourse during menstrual periods, exercise, or previous vaginal infections.

The number of new cases of toxic-shock syndrome being reported to the federal Centers for Disease Control has fallen off in recent months, but this may be because state health departments are now responsible for tabulating new cases and then reporting them to the Atlanta center.

Based on the disease's current frequency, the chance that a woman who uses tampons will get toxic-shock syndrome this year is about 9 in 100,000, according to Dr. Jeffrey Davis, the Wisconsin state epidemiologist who directed one study. But he said the disease is three times more common in women under 30.

The researchers said their recommendations to women remain the same: If a woman wants to virtually eliminate the risk of contracting the disease, she can stop using tampons. She can lower her risk by using tampons only during part of her period, or alternating with pads. Anyone who develops a toxic-shock symptoms while wearing a tampon should remove it and see a doctor at once.

The research, which was performed last summer but only now is being published in detail, leaves many questions unanswered concerning the disease, which has taken 66 lives and made hundreds ill. The studies' authors said they have no idea why using contraceptives reduces risk, nor do they know why only a tiny proportion of tampon-users get toxic-shock syndrome. They believe some other risk factor is still eluding them.

"I don't think any of us believe that if women went out and started using some method of birth control, they would stop developing toxic-shock syndrome," said Dr. Kathryn Shands, who conducted the second study as head of the toxic-shock task force at the Centers for Disease Control.

Shands said that although fewer toxic-shock victims used any contraception compared to healthy women, there is probably some other reason why using tampons allowed a toxin-producing bacterium to colonize the vagina and trigger the illness.

Shands and other experts believe toxic-shock syndrome is caused by a new strain of staphylococcus bacteria that first appeared in the mid-1970s, coincident with the first cases of the illness. Menstruation somehow promotes growth of the bacteria, which manufacture a toxin that enters the bloodstream and produces the symptoms: first fever, vomiting and diarrhea, then a sunburn-like rash and a drop in blood pressure that can be severe enough to cause shock and organ damage.

Staphylococcus bacteria isolated from victims in the two studies showed a similar pattern of sensitivity to antibiotic drugs, and a majority of the bacteria sampled in one study belonged to a single subgroup of the staphylococcus family.

In both studies, tampon use was implicated as a risk factor: 97 percent of patients in one study, and 100 percent in the other, used tampons, a significantly higher proportion than among women who remained well. Although other research implicated Rely tampons more than other brands, the victims studied in these reports included users of all tampon brands. Researchers found no connection between the illness and superabsorbent or deodorized tampons, and no evidence that victims either left tampons in longer or changed them more often.