key: cord-0941668-fyc9st58
authors: Petrarca, Laura; Nenna, Raffaella; Frassanito, Antonella; Pierangeli, Alessandra; Leonardi, Salvatore; Scagnolari, Carolina; Antonelli, Guido; Papoff, Paola; Moretti, Corrado; Midulla, Fabio
title: Acute bronchiolitis: Influence of viral co‐infection in infants hospitalized over 12 consecutive epidemic seasons
date: 2017-12-11
journal: J Med Virol
DOI: 10.1002/jmv.24994
sha: 0d2a78334cc47308d3794bd212485df96df085c4
doc_id: 941668
cord_uid: fyc9st58

Bronchiolitis is the first lower respiratory tract viral infection manifesting in infants younger than 12 months of age. Our aim was to evaluate clinical and serological differences in infants with bronchiolitis from a single or from multiple viruses. Our secondary aim was to investigate differences in recurrent wheezing episodes after 12‐24‐36 months of follow‐up. We reviewed the clinical records for 486 full‐term infants hospitalized for bronchiolitis with at least one virus detected in the nasopharyngeal aspirate. In 431 (88.7%) patients one virus was detected and in 55 (11.3%) infants more than one virus was found. No differences were observed in the length of hospitalization, clinical severity score, O(2) supplementation or admission to the intensive care unit. Single virus was associated with higher serum C‐reactive protein (C‐RP) than infants with multiple viruses and higher blood neutrophil counts. Respiratory syncytial virus (RSV) was the most frequently detected virus. RSV alone was associated with higher C‐RP (P = 0.007), compared to RSV coinfection. Infants with human rhinovirus (hRV) alone had higher white blood cell counts, higher blood neutrophils, and higher serum C‐RP levels than hRV co‐infection (P = 0.029, P = 0.008, P = 0.008). RSV + hRV, the most frequent co‐infection, was associated with lower neutrophil count and lower C‐RP levels (P = 0.008, P = 0.016) and less fever (P = 0.012), when comparing RSV versus hRV versus RSV + hRV. No differences were found in the frequency of recurrent wheezing between single versus multiple viruses after bronchiolitis. Our findings suggest that in infants with bronchiolitis multiple viral co‐infections can occur, without influence in the clinical severity of the disease. Infants with co‐infection seems to mount a lower inflammatory response.

illnesses, whereas others describe no influence on clinical presentation, [5] [6] [7] [8] [9] considering a non-homogeneous population of children aged less than 24 months.

In a previous study from our group, among 182 infants hospitalized for bronchiolitis, 14.4% had a viral co-infection, RSV + human bocavirus (hBoV). Infants with RSV + hBoV bronchiolitis had significantly higher clinical severity scores at admission and longer hospital stay, than those with human rhinovirus (hRV) and hBoV bronchiolitis. Infants with hRV bronchiolitis had higher eosinophil blood counts than infants with RSV and RSV + hBoV bronchiolitis. 2 Preliminary data showed that in infants with bronchiolitis, single and multiple viral infections manifest with similar clinical illnesses, however infants with a single virus had higher serum C-reactive protein (C-RP) than infants with multiple viruses, higher blood neutrophil numbers, and more frequently manifested fever. 10 Around 40-50% of infants hospitalized for bronchiolitis will have wheezing episodes in the first year of life. Although ample literature describes RSV, hRV, and the presence of higher blood eosinophil counts as factors predisposing to recurrent wheezing after bronchiolitis, 11 Our main aim in this study was to seek possible clinical or serological differences in a large series of infants with bronchiolitis from single and multiple viral infections. As the secondary outcome measure we compared the presence of wheezing at 12-24-36 months after bronchiolitis in infants with single and multiple viral detection.

We reviewed the clinical records for 486 full-term infants (263 boys, median age 2.03 months, range: 0.23-11.17) hospitalized for bronchiolitis in the Paediatric Emergency Department at "Sapienza" University Rome during 12 consecutive annual epidemic periods Bronchiolitis was clinically defined as the first episode of acute lower respiratory tract infection, characterized by the acute onset of cough, tachypnea, retraction, and diffuse crackles on chest auscultation in infants younger than 12 months. 13 Exclusion criteria were prematurity and underlying chronic diseases, such as cystic fibrosis, interstitial lung disease, congenital heart disease, and immunodeficiency.

To infants' parents, we administered a structured questionnaire seeking demographic information including age, gender, breastfeeding history, family smoking habits, family history for asthma, and atopy. On admission, we collected from the records the following clinical and serological data: total white blood cell count, blood neutrophil count, blood lymphocyte count, blood eosinophil count, C-reactive protein (C-RP), sodium serum level, chest radiological findings, and number of days hospitalization. On admission to hospital, each infant was assigned a clinical severity score ranging from 0 to 8 according to respiratory rate, arterial oxygen saturation on room air, presence of retractions, and ability to feed. 2 When clinically necessary, a chest x-ray was obtained at the Emergency Department, before hospitalization. 

Categorical variables such as number and percentages, and continuous variables values were expressed as median and range. A χ 2 test was run 

In 431 (88.7%) patients, RT-PCR detected only one virus and in 55 (11.3%) infants more than one virus. RSV was more frequently detected virus as a single than as a multiple viral infection (87.3%) ( Figures 1A and 1B) .

The most frequently isolated virus was RSV (365/486, 75.1%), followed by hRV detected in 89 infants (18.3%).

No differences were found in hospitalization stay, clinical severity score, O 2 supplementation and Paediatric intensive care unit (PICU) admission (Table 1) . Infants with co-infection presented less frequently fever (P = 0.05, by χ 2 test). Infants with a single virus infection had a higher serum C-RP level than infants with multiple virus infections (P = 0.012), higher blood neutrophil numbers (P = 0.005, by a non-parametric median test). The questionnaire answers indicated that children with multiple viral infections more frequently had a positive family history of asthma than those with a single virus infection (34.5% vs 22.2%, P = 0.043) ( Figure 1 ). When PCR detected RSV as a single virus it was associated with a higher C-RP level, than RSV associated with other viruses (P = 0.007) ( Table 2 ).

hRV was isolated in 60 infants as a single virus. hRV alone was associated with higher frequency of fever (P = n.s.), higher blood cell counts, higher neutrophils in the peripheral blood and higher C-RP levels than hRV coinfection (P = 0.029, P = 0.008, and P = 0.008). No differences were found for the median clinical severity score, nor for days hospitalization, nor for PICU admission, nor for O 2 supplementation.

In 29 (32.6%) infants hRV was isolated as a viral co-infection ( Figures 1A and 1B) . The most frequent co-infection was hRV + RSV in 20, followed by hRV + MPV in 5, hRV + PI in 1, hRV + AdV in 1, hRV + hBoV in 1, and hRV + RSV + MPV in 1. Infants who had an hRV coinfection more frequently had a positive family history of asthma than those with a single infection (41.4 vs 13.3%, P = 0.003). Infants with hRV alone more frequently had an eosinophil blood count higher than 400/mm 3 than those with a coinfection (18.3% vs 6.9%, P = ns) ( when comparing RSV versus RV versus RSV + hRV. Children with coinfection less frequently had fever than those with single infections (P = 0.012). The co-infection was associated with lower total white blood cell counts (P = n.s), lower neutrophil numbers in the peripheral blood, lower lymphocyte counts, and lower C-RP levels than the single infection (P = 0.008, P = ns, and P = 0.016). Infants with hRV detection alone more frequently had an eosinophil blood count higher than 400/mm 3 (P = 0.021) than those with RSV and RSV + hRV infections (Table 4 ).

In our study, 11.3% of the nasal swabs from the 486 full-term infants hospitalized for bronchiolitis prospectively and consecutively enrolled over 12 epidemic seasons contained a viral co-infection. Although we found no differences in clinical severity scores between infants with single or multiple viral infections, infants in whom RT-PCR detected multiple infections seemed to have a lower inflammatory response than those with single infections. No differences were found between the two groups for recurrent wheezing episodes.

The viral co-infection rate in this study is considerably lower than most reported rates. In children younger than 24 months with bronchiolitis, Chen et al 5 When we analyzed data for emerging and less frequently studied viruses, we detected hBoV more frequently as a co-infection than as infection. They also enrolled preterm infants or infants with underlying chronic disease, in whom they more frequently detected a multiple viral infection. In our previous paper in a smaller sample 2 we found a higher clinical severity score and longer hospital stay in 15 infants with RSV + hBoV, than in infants with RSV, hRV, hBoV infection alone.

Laboratory data analysis highlighted a higher neutrophil count and higher C-RP levels in infants with a single infection than in 21 but further studies are needed to clarify whether these two factors are involved in the clinical presentation of bronchiolitis with multiple viral detection. In accordance with our previous findings, 2 in our series infants hospitalized for hRV bronchiolitis alone more frequently had an eosinophil blood cell count higher than 400/mm 3 , and more frequently a higher prevalence of family history for atopy than in co-infection, but not statistically significant. These findings could suggest that severe hRV infections preferentially manifest in infants predisposed to atopy.

We also evaluated the possible correlation between co-infections and recurrent wheezing, hypothesizing that multiple viral infection might cause a more severe inflammation and this results in a higher recurrence of wheezing episodes. We found no association between co-infection and recurrent wheezing, despite the higher family history for asthma, in patients infected with a mixed than with a single virus.

This previously unreported finding suggests that recurrent wheezing after bronchiolitis depends on the type of virus the infants were found positive to, regardless of whether it was detected as a single or as a multiple virus. We previously reported a positive association between recurrent wheezing after bronchiolitis and hRV detection 11 and in a later study a higher RSV-RNA load. 12 This issue merits clarification in a study with a larger number of cases and a longer follow-up. In conclusion, our study shows that many infants with bronchiolitis (about 11%) in Rome, Italy are infected with multiple virus. No significant differences in clinical severity distinguish bronchiolitis in infants infected with single or multiple virus. Although co-infected infants seem to mount a lower inflammatory response than those without co-infections the immunological response to virus coinfection merits further in vitro studies. Co-infection seems not to influence the clinical presentation of bronchiolitis nor the recurrence of wheezing episodes after three years of follow-up.

We thanks Alice Crossman for her support with the English revision.

The authors have no conflicts of interest to declare.

What is known about this topic 

Our study shows that multiple viruses detection (11.3%) in infants with bronchiolitis defined restrictively in Rome (Italy) is lower than compared to literature. No significant differences in clinical severity distinguish bronchiolitis in infants infected with single or multiple virus.

Co-infected infants seem to mount a lower inflammatory response than those without co-infections. Co-infection seems not to influence the clinical presentation of bronchiolitis nor the recurrence of wheezing episodes after three years of follow-up.

ORCID Fabio Midulla http://orcid.org/0000-0001-7476-5266

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