Efficacy of IntraVenous ImmunoGlobulins in Toxic Shock Syndromes: a Paediatric Pilot Study

Overview

Staphylococcus aureus and Streptococcus pyogenes produce many virulence factors. Some of them are responsible for severe infections in humans. Superantigen toxins synthesized by S. aureus or by S. pyogenes, are responsible for toxic shock syndromes (TSS) which lethality can attain 25% in children with validated criteria of septic shock. Previous studies, performed in vitro and in vivo in animals, have shown that Intravenous immunoglobulins \[IVIG\] contain antibodies \[Ab\] against these toxins and, when used at high concentration, IVIG are able to neutralize their toxicity. However, in all these studies, IVIG administration has been preventive and there is no reliable data demonstrating their therapeutic efficacy in vitro or in vivo in humans or in animals, once the disease is present. The efficacy of IVIG is established in other pathologies for which the role of the superantigens \[superAg\] is suspected, like Kawasaki disease in children. The mechanism of action, although not perfectly known, involves at the same time a direct effect on superAg (Ag-Ab complex) and indirect effects like the neutralisation of superAg within the network of anti-idiotype Ab or the neutralisation of the T-cells receptors. Staphylococcal and streptococcal toxic shocks imply bacterial exotoxins that are superAg. It seems thus consistent to imagine a same type of treatment with IVIG. However, there is currently no evidence of the efficacy of IVIG in this indication. One of the explanations relies on the lack of statistical power of previous adult studies, which principal objective was to show a reduction of the mortality. Taking into account the low prevalence of TSS, it has been hard to recruit enough patients to have the required statistical power. Moreover, some works have been extracted from larger studies on septic shock and the definitions of the TSS were nor always very reliable. Lastly, if the investigators consider the definition of the TSS as mentioned by the " Centre for Disease Control " \[CDC\], for which any hypotension, even a simple orthostatic hypotension, serves the diagnosis of TSS as long as the other symptoms are present, it is obvious that many patients are likely to be recruited in a study although it is highly probable that their health will get better with a " standard " treatment. The definition of a " real " TSS can be refined, keeping the CDC criteria, but changing the hypotension criterion in a more accurate criterion as described in the " surviving sepsis campaign ", internationally accepted and based on norms adapted to the age for paediatric forms. IVIG therapy is very expensive and TSS is not recognized as indication of IVIG according to their marketing authorization. The feasibility of a randomized controlled study with this treatment needs to be assessed as it would be hazardous to conduct a large prospective RCT without having first assessed this feasibility in terms of recruitment rates, consent rates or compliance rates. Inclusion, randomisation and collect of inform consent in the context of severe shock are challenging and require evaluation of feasibility. The sample size calculation of the large study on mortality required estimations of the event in the specific population of children with criteria of septic shock. Surrogates markers of outcome need to be better defined. For example it would be useful to determine the evolution of organ dysfunctions with and without IVIG treatment in this population. Various organ failure scores, used upon admission and later on, have been validated in adults and in children. The absence of improvement of the Paediatric logistic organ dysfunction (Pelod) score over time is a good indicator of mortality in Paediatric intensive care unit (PICU). It could be used as surrogate marker to evaluate the efficacy of IVIG.