Each year in the US alone, several thousand women develop menstrual toxic shock. The symptoms include fever, vomiting and, in 5 per cent of cases, lethal organ failure. The illness is caused by build-up of the toxin TSST-1. It is made by Staphylococcus aureus bacteria, which usually live harmlessly in the anaerobic conditions of the vagina but ramp up production of the toxin when exposed to the air trapped in tampons.
But why do so few of the estimated 50 million women in the US using tampons get ill? Almost certainly because only a few are genetically susceptible, claims a team at the University of Tennessee in Memphis funded by Procter & Gamble, the maker of Tampax.
Last week the researchers told a meeting in Chicago organised by the American Society for Microbiology that blood and vaginal swabs taken from 19 women with menstrual toxic shock lacked the antibodies capable of blocking TSST-1,and only two of the patients developed antibodies while they were recovering.
However, 35 of 39 healthy women did have high levels of effective antibodies. Philip Tierno, the microbiologist at New York University who first uncovered the link between tampons and toxic shock syndrome, disputes the team's claims. "The reason most patients do not develop antibodies is because the toxin prevents antibody formation," he says.
TSST-1 is a superantigen, meaning that high levels can trigger an immune overreaction, preventing antibody production. But the P&G team thinks the lack of antibodies could be linked to a deficit of a protein called complement in the patients' blood.