The great plague that ravaged ancient Athens, weakening the city-state so that it fell to Sparta in the Peloponnesian Wars, was caused by simultaneous epidemics of influenza and toxic shock syndrome, a retired epidemiologist is claiming in the New England Journal of Medicine.

The cause of the plague, which persisted from 430 B.C. to 427 B.C., has been a subject of speculation for centuries. Smallpox, bubonic plague, scarlet fever, measles and typhus have all been proposed as causes. Some experts have argued that the mysterious combination of symptoms described by Thucydides, the Athenian historian who survived the epidemic, fits no known disease and that the causative organism is extinct or has evolved into something different.

"It fits all the criteria, epidemiologically and clinically, for influenza complicated by toxic shock syndrome," said Dr. Alexander D. Langmuir, former chief of epidemiology for the federal Centers for Disease Control in Atlanta.

According to Thucydides, the symptoms included fever, coughing, vomiting, blisters, thirst, diarrhea, gangrene and amnesia. According to Langmuir gangrene provides the key. It is not a common feature of the other candidates but is of toxic shock.

Toxic shock syndrome, first recognized in 1978 among women using high-absorbency tampons, is caused by a form of the Staphylococcus bacterium. Normally a skin-dweller in low numbers, the bacteria, which secrete a toxin, can cause disease if allowed to grow to large numbers, which can happen if they get under the skin.

Langmuir speculates that the Athenians, debilitated by severe flu, succumbed to "staph" infections through small cuts or in irritated nasal passages. The Athenian plague, often called Thucydides syndrome, may still be causing disease, he warns, and doctors should be aware of the possible combination.