Staphylococcal toxic shock syndrome: still a problem

Comment: As noted by MacIsaac et al above, my colleagues and I recently reported an increase in the incidence of staphylococcal toxic shock syndrome (TSS) in Minneapolis–St Paul in the United States, from 0.8 per 100 000 (in January 2000) to 3.4 per 100 000 (in December 2003).1 We noted that physicians across the United States were reporting TSS cases in increasing frequency.

There are two major categories of staphylococcal TSS, menstrual and non-menstrual.2,3 Menstrual TSS is defined as occurring during menstruation or within the 2 days preceding its onset or the 2 days following its cessation; the illness is primarily, but not exclusively, associated with tampon use. Menstrual TSS is nearly always caused by the superantigen exotoxin, TSS toxin-1 (TSST-1).4 Superantigens significantly overactivate the human immune system to release cytokines that cause the clinical features of TSS (interleukin-1β [endogenous pyrogen]; tumor necrosis factor-α and β [capillary leak]; and interferon-γ and interleukin-2 [rash]).5 Non-menstrual TSS may occur in anyone, young or old, male or female, and today commonly follows superinfection of the upper respiratory tract after viral infection. Non-menstrual TSS is caused by TSST-1 (50%) or by staphylococcal enterotoxin B or C (together nearly 50%).

The important question is what accounts for the fourfold rise in TSS that was reported in our 2004 study? We proposed several hypotheses. First, the increase in incidence partly results from the emergence of three strains of methicillin-resistant Staphylococcus aureus (MRSA), at least two of which are emerging worldwide. These strains are termed (by Centers for Disease Control [CDC] nomenclature) USA 1100 (TSST-1 positive), USA 400 (SEB/SEC, Panton–Valentine leukocidin [PVL] positive), and USA 300 (positive for an unknown superantigen as well as PVL).

In our studies, USA 1100 strains currently comprise 20% of submitted isolates, compared with none before the year 2000. These isolates may produce 10 to 100 times more TSST-1 in vitro than their methicillin-sensitive S. aureus counterparts matched by pulsed-field gel electrophoresis profile. Thus, these organisms rapidly produce high levels of TSST-1, leading to TSS even when lower-absorbency tampons are used. In addition, the USA 400 and USA 300 strains are also emerging and are associated with increases in non-menstrual TSS. These latter isolates also produce more superantigens than their methicillin-susceptible counterparts.

Secondly, in our 2004 study, physicians who submitted cultures to our laboratory defined cases of TSS based on patient presentation and the presence of an S. aureus strain producing one of the three causative exotoxins. Our TSS definition is likely to be broader than the strict CDC definition.

Finally, we also noted that it is possible that women are beginning to menstruate and to use tampons at earlier ages. In addition, teenagers are bombarded with media advice that TSS is no longer a problem; failure to recognise the illness may lead to it becoming more severe before presentation. These lifestyle and awareness changes, combined with the emergence of high-toxin-producing strains and the expanded definition of TSS, may account for the observed increase in TSS. The increase does not appear to be caused by changes in tampon composition or absorbency.