MALMO, SWEDEN – Methicillin-resistant Staphylococcus aureus gets the blame in the Americas as the main cause of a great wave of community-acquired severe invasive staphylococcal infections in children and adolescents during the past nearly 2 decades, but many European pediatric infectious disease specialists believe that Panton-Valentine leukocidin (PVL), a frequent co-traveler with MRSA, is the true bad actor.
“The American literature focused first on MRSA, but we’ve seen very similar, very severe cases with MSSA [methicillin-susceptible S. aureus] PVL-positive and MRSA PVL-positive infections,” Pablo Rojo, MD, PhD, said at the annual meeting of the European Society for Paediatric Infectious Diseases.
“It is only because at the beginning there were so many MRSA cases in the States that they thought that was the driver of the disease. It is still unclear. There is still a discussion. But I wanted to bring you my opinion and that of many other authors that it’s mostly PVL-associated,” added Dr. Rojo of Complutense University in Madrid.
He was senior author of a multinational European and Israeli prospective study of risk factors associated with the severity of invasive community-acquired S. aureus infections in children, with invasive infection being defined as hospitalization for an infection with S. aureus isolated from a normally sterile body site such as blood, bone, or cerebrospinal fluid, or S. aureus pneumonia. They identified 152 affected children, 17% of whom had severe community-acquired invasive S. aureus, defined by death or admission to a pediatric intensive care unit due to respiratory failure or hemodynamic instability.
The prevalence of PVL-positive S. aureus infection in the overall invasive infection group was 19%, while 8% of the isolates were MRSA.while MRSA was not associated with a significantly increased risk. The other independent risk factors for severe outcome were pneumonia, with an adjusted 13-fold increased risk, and leukopenia at admission, with an associated 18-fold risk ( ).
Of note, the virulence of PVL stems from the pore-forming toxin’s ability to lyse white blood cells. Because a leukocyte count is always available once a patient reaches the ED, severe leukopenia as defined by a count of less than 3,000 cells/mm3 at admission becomes a useful early marker of the likely severity of any case of S. aureus invasive disease, according to Dr. Rojo.
He highlighted four key syndromes involving severe invasive S. aureus infection in previously healthy children and adolescents that entail a high likelihood of being PVL positive and should cause physicians to run – not walk – to start appropriate empiric therapy. He also described the treatment regimen that he and other European thought leaders recommend for severe PVL-positive S. aureus invasive infections.
The microbiologic diagnosis of PVL can be made by ELISA (enzyme-linked immunoassay) to detect the toxin in an S. aureus isolate, by a rapid monoclonal antibody test, or by polymerase chain reaction to detect PVL genes in an S. aureus isolate. But don’t wait for test results to initiate treatment because these are high-mortality syndromes, he advised.
“Many people tell me, ‘My lab doesn’t have a way to diagnose PVL.’ And it’s true, it’s not available in real life at many hospitals. My message to you is that you don’t need to wait for a microbiological diagnosis or the results to come back from a sample you have sent to the reference lab in the main referral center. We can base our diagnosis and decision to treat on clinical grounds if we focus on these four very uncommon syndromes involving invasive S. aureus infection. I think if you have any child with these symptoms you have to manage them on the assumption that PVL is present,” said Dr. Rojo, principal investigator of the European Project on Invasive S. aureus Pediatric Infections.