Toxic shock syndrome is causing almost as much illness as it did during the height of the scare in 1980, and the products some authorities blame for it -- high absorbency tampons -- are selling nearly as well as ever.

Starting Dec. 20, the Food and Drug Administration for the first time will require manufacturers to print notices on or inside tampon packages advising women to use only the least absorbent kind needed.

Although toxic shock syndrome (TSS) once caused near hysteria, it is now almost ignored.

This is partly because women have become accustomed to the convenience of tampons, and giving up familiar brands because of a slight chance of developing toxic shock syndrome seems almost as preposterous as walking to avoid the danger of car accidents. "You can't tell young women not to use tampons," an FDA doctor said. "That's part of their culture now."

Physicians, it is true, are not reporting toxic shock cases to state health departments as often as they once did, medical statisticians said, so reported totals are down in some states.

But latest figures from the federal Centers for Disease Control (CDC) in Atlanta show that about 50 cases a month still are occurring, with a 3.3 percent fatality rate. Surveillance in Minnesota, a state that carefully monitors all hospital admissions, shows almost as many cases as in early 1981, when the nation was still in the throes of the toxic shock scare.

The subject is still one of mystery and medical controversy. The Journal of the American Medical Association recently aired the views of Yale statisticians who think the case against tampons is biased and unproved.

They said that all the early publicity about toxic shock syndrome strongly linked it with menstruation and, soon, with tampons. They said this could have biased all subsequent observations simply by alerting women and doctors to suspect the disease following tampon use.

What are the facts? From a strict scientific viewpoint, they remain uncertain. The subject is new and no one can claim true "proof" of almost anything about this disease.

And yet:

* The overwhelming majority of medical officials and investigators believe more strongly than ever that tampon use is associated with most cases. This majority includes CDC officials in Atlanta as well as members of an Institute of Medicine study group at the National Academy of Sciences.

* The Minnesota Health Department, which has continued to search for all toxic shock cases, is convinced that high-absorbency tampons continue to be the main triggers of infection, with the amount of absorbency the key to how risky a product is.

* The disease, however, is not exclusively one of women, or women using tampons, though women are more affected than men, and women aged 15 to 24 are most affected. Some cases occur in menstruating women not using tampons; some in women after childbirth. In men and women, other cases are mainly associated with infections from burns, boils, cuts, abscesses, insect bites, and "you name it," one health official said.

* The guilty "bug" in all cases is apparently a particular strain of staphylococcus, possibly one that either first appeared or first flourished in the late 1970s. The staph bug produces a toxin or toxins that cause the symptoms. Most cases respond to antibiotics, though in a few there may be long-term ill effects.

The disease is still uncommon, as diseases go. By official statistics, even tampon-using women have only about one chance in 10,000 of contracting it in a given 12-month period. The actual risk may be five to 10 times greater -- there is good evidence that several thousands of cases are going unreported -- but the threat of contracting toxic shock syndrome still is not great.

The very name toxic shock syndrome was unknown until 1978 but by June, 1980, CDC had counted 130 victims. Two months later, at the height of the scare, CDC confirmed 131 cases. By early 1981 the number had dropped to around 50 a month, and it has stayed close to that.

The typical symptoms include sudden fever, vomiting and/or diarrhea, sometimes headache, sore throat and aching muscles, then within a few days a red, sunburn-like rash and, often, severely falling blood pressure, the "shock" part of the disease, causing kidney failure and disorientation.

In June, 1980, CDC epidemiologists determined that most of the victims -- like more than 70 percent of the 70 million American women of menstrual age -- used tampons. In September, when it became clear that Procter & Gamble's high absorbency Rely was the tampon most (but far from entirely) involved, the manufacturer ended Rely sales.

P&G still maintains there was "no defect" in Rely. It is still fighting lawsuits by affected women or families. So far, it has appealed a $300,000 award to one woman's survivors. It settled another case out of court.

CDC epidemiologists continue to think Rely Super was the riskiest tampon. However, Dr. Michael Osterholm of the highly regarded Minnesota Health Department maintains that Rely was identified principally because it had the lion's share of "the high-absorbency market."

"The risk of TSS was more closely associated with tampon fluid capacity (absorbency)" than with any one brand, Osterholm wrote in the April Journal of Infectious Diseases.

Osterholm also studied the absorbency of tampons made in 1979-1980. Playtex Super Plus, o.b. Super Plus, Tampax Super Plus, Kotex Super and Playtex Super were all in the highest-absorbency group with Rely Super. In a mid-group were o.b. Super and Playtex Regular; in a somewhat lower absorbency group, Kotex Regular, o.b. Regular, Tampax Super and, the least absorbent, Tampax Slender. Since then, he says, Kotex has reduced absorbency and one other maker, which he said he cannot name, has increased it somewhat.

CDC's Dr. Arthur Reingold calls the Minnesota evidence against absorbency "interesting" and demanding of more study but still unproved. A CDC comparison of 50 affected women with 150 who were unaffected detected no connection with tampon absorbency.

But the CDC study was a small one, and the American College of Obstetrics and Gynecology told women in October, 1980, "it would be prudent, at present, to discontinue the use of the newly developed, super-absorbent tampons." The Institute of Medicine group last June advised "minimizing" use of high absorbency products.