Conference Coverage

Whole blood PCR improves diagnosis of pediatric bacterial sepsis


 

AT ESPID 2017

– Whole blood multiplex polymerase chain reaction (PCR) holds considerable promise as a rapid noninvasive test to improve diagnosis of life-threatening bacterial infections in children with suspected sepsis yet negative blood cultures, Clare Thakker, MD, reported at the annual meeting of the European Society for Paediatric Infectious Diseases.

There are several disadvantages with blood cultures – the current diagnostic standard. The turnaround time is 48 hours or longer. Moreover, false-negative culture results are common because of prior antibiotic therapy. And blood cultures require a considerable amount of blood, which becomes an issue in younger children with small blood volumes. Whole blood PCR is unfettered by these limitations, and it could reduce the need for invasive sampling, such as pleural or joint aspiration or CSF sampling, in blood culture–negative children, observed Dr. Thakker of Imperial College London.

Dr. Clare Thakker of Imperial College London Bruce Jancin/Frontline Medical News

Dr. Clare Thakker

She presented an analysis from EUCLIDS (the European Union Childhood Life-Threatening Diseases Study), an ongoing multinational 5-year genomic study involving more than 6,000 children. The study (www.euclids-project.eu) has two broad aims: to understand why some children with an infection develop severe illness while others don’t, and to develop improved diagnostic methods for these infections.

The challenge posed by febrile children is that even though the vast majority will turn out to have a self-limited viral illness, a small proportion will have a life-threatening bacterial infection. And distinguishing between the two groups in timely fashion often remains difficult today, the pediatrician said.

Dr. Thakker reported on 504 EUCLIDS participants with suspected sepsis who had blood cultures and whole blood PCR testing done on the same day. The multiplex PCR, developed by Micropathology of Coventry, England, was set up to test simultaneously for five clinically important bacterial pathogens: Neisseria meningitidis, Streptococcus pneumoniae, S. pyogenes, Staphylococcus aureus, and Haemophilus influenzae. Prior to testing, the blood samples underwent lysozyme/lysostaphin digestion and silica bead disruption in order to break down cell walls and facilitate nucleic acid extraction.

Of the 504 children with suspected sepsis, 438 (87%) had negative blood cultures, among whom were 326 patients (74%) with clinically suspected or definite bacterial infection. The PCR test identified one of the five target pathogens in 25 of the 326 patients (8%) where physicians suspected bacterial sepsis despite negative cultures. Ten blood culture-negative patients (40%) were whole blood PCR positive for N. meningitidis, 6 (24%) for H. influenzae, 5 (20%) for S. pneumoniae, 3 (12%) for S. aureus, and 1 (4%) for S. pyogenes. Three of the 25 positive tests showed poor clinical correlation consistent with environmental contamination. The other 22 positive PCR results were consistent with the patient’s clinical syndrome – for example, N. meningitidis being found in the blood of a child with meningeal encephalitis – or concordant with the results of a culture obtained invasively at a sterile body site.

Ninety-two patients with negative blood cultures were culture positive for a causative bacterial pathogen obtained by invasive sampling of a sterile body site such as the CSF. In 68 of these 92 cases (74%), the pathogen was among those on the multiplex PCR panel.

“Our study results bring into question whether blood culture should be the gold standard; clearly, blood culture is not capturing everything. Our findings also highlight the need for developing additional diagnostic markers, maybe based upon the host inflammatory response, to delineate which of these detections are pathogens and which are passengers,” Dr. Thakker said.

She reported having no relevant financial conflicts regarding the European Union–sponsored study.

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