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Enteroviruses (EV) are single-strained RNA viruses that belong to the Picornaviridae family, a large virus family composed of more than 70 serotypes. These viruses remain a major cause of febrile illness in children. Most of these infections are subclinical but they can also cause severe disease [1,2]. The highest attack rates occur in children aged <1 year. The reported prevalence of EV infection in patients <12 months with a febrile event ranges from 15% to 50% [1,3,4].
Fever without source (FWS) is one of the most frequent reasons for consultation in paediatric emergencies, especially in infants younger than 3 months. These patients have very unspecific clinical signs, fever commonly being the only clinical manifestation of the disease. About 8.5% of infants aged under 90 days with fever will develop a potentially severe invasive bacterial infection (IBI) [5,6]. Considering these data, and according to published guidelines , these patients usually undergo aggressive diagnostic and therapeutic procedures in the emergency room. EV infections may mimic bacterial disease and often lead to unnecessary diagnostic testing and antibiotic use, until a bacterial infection has been ruled out. The ability to diagnose viral infections has improved substantially in recent years, and because most febrile infants are presumed to have viral infections, reaching a specific diagnosis could contribute significantly to their management. In fact, it is known that the diagnosis of a viral infection reduces the risk of suffering from IBI [6,8]. Similarly, we recently reported a lower risk of positive blood or urine cultures among infants with a positive rapid influenza test , as previously described in febrile infants with respiratory syncytial virus (RSV) infection [10,11]. In this study, we aimed to determine the prevalence rate of EV infection among febrile infants aged <90 days in our setting, by including an EV real-time polymerase chain reaction (RT-PCR) technique in the routine evaluation of these patients in the Emergency Room. We also aimed to study how often EV and IBI co-infections occur in these patients.
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During the 24-month study period, a total of 381 (179 females, 47%; mean age: 35 days, standard deviation (SD): 21 days) patients with FWS under 3 months of age, fulfilling inclusion criteria, were admitted to our centre and included in the study (Fig. 1). At admission, the mean (SD) of the fever peak was 38.4°C (0.2), with a median of 6 h (p25–75: 3–12 h) evolution. The most common complaints were rhinorrhea (27%), irritability (23%), refusal of food (21%) and gastrointestinal symptoms (19%).
Figure 1. Algorithm summarizing the patients included in the study according to final results regarding EV infection. EV, enterovirus; CSF, cerebrospinal fluid.
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Discharge diagnoses of all patients are summarized in Table 1.
Table 1. Discharge diagnosis
|Diagnosis|| n = 381||EV− (n = 317)||EV+ (n = 64)|
|Invasive bacterial infection|
| Urinary tract infection||65||64||1|
| Acute gastroenteritisb||4||4||0|
| Cutaneous cellulitis||1||1||0|
|Non-invasive bacterial infections: viral or presumable viral infections|
| Febrile syndrome without source||174||149||25|
| Aseptic meningitis||39||7||32|
| Acute gastroenteritis||27||24||3|
| Upper respiratory tract infection||24||22||2|
| Acute otitis media||15||15||0|
Blood and urine cultures were performed in all patients. Lumbar puncture was performed in 255 (74.8%) patients. Thirty (7.8%) positive blood cultures were observed; almost half of them (14 out of 30) were considered as contaminated. The remaining 16 blood cultures tested positive for: Streptococcus agalactiae (n = 6), Escherichia coli (n = 9) and Proteus mirabilis (n = 1). All gram-negative bacteraemias were secondary to urinary tract infections.
Urine cultures were positive in 65 cases: E. coli in 57 cases, Klebsiella pneumoniae in three cases, and K. oxytoca, Enterobacter cloacae, P. mirabilis, Citrobacter koseri and S. agalactiae in one case each.
Meningitis was diagnosed in 39 cases; all CSF bacterial cultures tested negative. Enteroviral meningitis was diagnosed in 32 out of 39 infants with CSF pleocytosis; in seven cases, no germ was identified.
Blood EV PCR was performed in all but 83 patients, either because of insufficient sampling or PCR inhibition; cerebrospinal fluid EV PCR was performed in 237 infants. Enterovirus infection was diagnosed in 64 patients (56.3% male; prevalence rate, 16.8%; 95% confidence interval (CI), 13.2–20.9%; Fig. 2), 44 (68.8%) of them during March to August (Fig. 2). Enterovirus was considered as the aetiology of FWS in 62 patients: FWS (n = 25), aseptic meningitis (n = 32), acute gastroenteritis (n = 3) and upper respiratory tract infection (n = 2). Co-infection occurred in two patients: a 27-day-old neonate with influenza A and EV co-infection, who was finally diagnosed with flu; and a 37-day-old infant with a urinary tract infection caused by S. agalactiae and an EV co-infection. Three infants, none of them EV-infected, required admission to the intensive care unit: a newborn aged 9 days with hypoxaemia secondary to RSV bronchiolitis that developed after admission; a 47-day-old infant because of urinary sepsis; and an infant aged 2 months, because of aseptic meningitis and secondary apnoeas. No patient died.
Comparison of patients with positive EV PCR and negative EV PCR
Age or clinical symptoms at presentation did not differ between EV-positive and EV-negative patients, except for exanthema (more common among EV-positive patients) and rhinorrhea (less common among EV-positive infants). Laboratory markers of infection were consistently lower in patients infected with EV (Table 2). It is important to note that only two infants with EV infection (finally diagnosed with sterile enteritis and FWS, respectively) showed PCT values higher than 2 ng/mL. The number of patients receiving empirical antibiotics at admission, the length of antibiotic therapy and duration of hospital stay did not differ between EV-positive and EV-negative patients.
Table 2. Clinical data and test results and management for the two groups
|Clinical||EV positive (n = 64)||EV negative (n = 317)||p|
| Fever (mean °C)||38.5||38.4||NS|
| Evolution (mean hours)||10.94||10.93||NS|
| Food refusal||15.9||23.9||NS|
| Rhinorrhoea|| 8.6||30.8||<0.001|
| Gastrointestinal symptoms||19||20||NS|
| Exanthema|| 6.9||1.7||<0.05|
| White blood cell count/mm3 (mean)||10 296||13 038||<0.001|
| Total neutrophil count/mm3 (mean)||4209||6300||<0.001|
| Band neutrophil count/mm3 (mean)||242||487||<0.005|
| CRP (mg/l) (mean)||12.8||25.7||<0.001|
| PCT (ng/dL) (mean)||0.58||1.80||<0.01|
| White CSF cells/mm3 (mean)||246.25||60.72||<0.05|
|Management and evolution|
| Antibiotic treatment||75.4%||73.4%||NS|
| Median length of antibiotic treatment (days)||2.4||2.9||NS|
| Median length of stay (days)||3.7||4.1||NS|
Prevalence of IBI
As previously mentioned, only one case of IBI was diagnosed, in one of the 64 patients diagnosed with EV infection (a 37-day-old infant with a urinary tract infection caused by S. agalactiae). This represents a 1.6% (95% CI: 0.04–8.4%) prevalence rate for IBI among EV-positive patients, significantly lower than the prevalence of IBI in EV-negative patients (80 out of 317 cases; 25.2%; 95% CI, 20.4–30.0%; p <0.001).
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The majority of febrile children who present at primary care and emergency departments are younger than 3 years of age. Twenty per cent of them have FWS, occult bacteraemia occurring in 3% of cases. The percentage of bacterial infections increases in infants aged <3 months, by up to 10% [5,7,16]. The evaluation and management of these infants are controversial because of the non-specificity of clinical symptoms and signs . In these infants, the most prevalent causes of fever are viral infections, which are associated with a reduction in the risk of IBI . Among them, EV remains a major cause of febrile illness [1,17]. However, recent guidelines on the management of infants with FWS do not include a systematic detection of viral infections in these patients .
To our knowledge, this is the first prospective study to investigate the role of EV infection in febrile infants under 90 days of age in our geographical area. Ahmed et al.  determined that PCR assay of CSF is useful for the rapid and reliable diagnosis of EV meningitis in these young infants, while Ritticher et al.  identified EV as the cause of FWS in 20% of young infants by means of EV PCR in blood and CSF samples. Both studies were performed in the United States. In our experience, EV infection was identified as the cause of fever in 64 of the 381 studied subjects; this prevalence rate (16.8%) is similar to that described in the literature [3,6,17,20,21]. Of note, most EV infections were observed from March to August, earlier in time than the classical EV season, which has usually been described as in the summer and fall months [17,22]. Patients diagnosed with EV were mostly newborns (56.3%), as Ritticher  described in her series. Twenty per cent of EV-infected patients were younger than 14 days and more than 37% were younger than 28 days. Rotbart  also described a high rate of EV infection (47%) in patients under 30 days of age. In our series, only three patients were 7 days old or less at the time of diagnosis of EV infection; most severe cases of EV-related illnesses have been described in these very young infants [2,24–26]. The rate of EV infection among neonates might have been overestimated in our study by the fact that lumbar puncture was systematically performed in all patients under 28 days, but not in those patients aged over 1 month.
In our cohort, 84.2% of cases of meningitis were caused by EV and, among all EV-positive patients, half of them were diagnosed with meningitis, as previously reported [18,19]. It is important to note that 41.6% of EV meningitis did not show pleocytosis, a finding that has been associated with young ages (<90 days) by other authors [17,22].
The IBI prevalence in EV-infected infants has been described as being close to 7%, mostly consisting of urinary tract infections [6,17,18,27]. We only detected one patient affected with a urinary tract infection (that had already been diagnosed and treated in the emergency room) and EV co-infection. Despite this, nearly 75% of EV-infected infants received intravenous antibiotic treatment for at least 72 h, pending the results of bacterial cultures, and length of stay was not different between EV-infected and uninfected children. The fact that EV PCR was performed in our laboratory only every 48–72 h, should not be forgotten. Similarly, Rotbart  reported that 94% of their cohort of EV-infected infants received at least one dose of parenteral antibiotic and more than 80% of them were admitted to hospital.
Other studies in EV-infected infants have shown a reduction in the number of days of hospitalization because of early obtaining of PCR results in the first 24 h after admission. Nigrovic and Chiang  demonstrated that when the prevalence of EV meningitis is higher than 6%, systematic EV determination by PCR is cost-effective as it prevents unnecessary antibiotic therapy and hospital admissions. King et al. , in a retrospective review of 478 patients aged <90 days in whom CSF EV PCR was determined, also concluded that confirmed EV meningitis would potentially reduce the length of stay and the duration of antibiotic treatment, as has been suggested by other authors as well [17,20,30].
Our study has several limitations, including its observational design, the fact that both CSF and blood EV PCR determination were not performed in all patients, and a potential under-diagnosis bias in infants with afebrile EV infection. Finally, other viral co-infections were not systematically investigated and probably were missed in some cases.
In summary, our results suggest that febrile infants (<90 days) diagnosed with EV infection show a low risk of IBI when compared with uninfected patients. The systematic investigation of EV infection in young infants with FWS in the emergency department during March to August, when the prevalence of EV infection is higher in our geographical area, may allow a more conservative approach to the management of these patients, and ultimately, decrease the need for antibiotic use and the length of hospitalization. Until randomized clinical trials on this issue are available, current recommendations on the management of young infants with FWS should be strictly followed.