ABSTRACT: BACKGROUND:Enteroviruses are the most frequent cause of acute meningitis and are seen increasingly in sepsis-like disease and fever without source in the paediatric population. Detection of enterovirus in cerebrospinal fluid (CSF) specimens by PCR is the gold standard diagnostic test. Our aim was to assess a method of detecting enterovirus in blood specimens by PCR. METHODS:We did a prospective, multicentre, observational study at 35 French paediatric and emergency departments in 16 hospitals. We recruited newborn babies (aged ?28 days) and infants (aged >28 days to ?2 years) with fever without source, sepsis-like disease, or suspected meningitis, and children (aged >2 years to ?16 years) with suspected meningitis, who were admitted to a participating hospital. We used a standardised form to obtain demographic, clinical, and laboratory data, which were anonymised. Enterovirus PCR testing was done in blood and CSF specimens. FINDINGS:Between June 1, 2015, and Oct 31, 2015, and between June 1, 2016, and Oct 31, 2016, we enrolled 822 patients, of whom 672 had enterovirus PCR testing done in blood and CSF specimens. Enterovirus was detected in 317 (47%) patients in either blood or CSF, or both (71 newborn babies, 83 infants, and 163 children). Detection of enterovirus was more frequent in blood samples than in CSF specimens of newborn babies (70 [99%] of 71 vs 62 [87%] of 71; p=0·011) and infants (76 [92%] of 83 vs 62 [75%] of 83; p=0·008), and was less frequent in blood samples than in CSF specimens of children (90 [55%] of 163 vs 148 [91%] of 163; p<0·0001). Detection of enterovirus was more frequent in blood samples than in CSF specimens of infants aged 2 years or younger with fever without source (55 [100%] of 55 vs 41 [75%] of 55; p=0·0002) or with sepsis-like disease (16 [100%] of 16 vs nine [56%] of 16; p=0·008). Detection of enterovirus was less frequent in blood than in CSF of patients with suspected meningitis (165 [67%] of 246 vs 222 [90%] of 246; p<0·0001). INTERPRETATION:Testing for enterovirus in blood by PCR should be an integral part of clinical practice guidelines for infants aged 2 years or younger. This testing could decrease the length of hospital stay and reduce exposure to antibiotics for low-risk patients admitted to the emergency department with febrile illness. FUNDING:University Hospital Clermont-Ferrand.