Epidemiological and clinical features of respiratory viral infections in hospitalized children during the circulation of influenza virus A(H1N1) 2009
Seasonal influenza viruses and respiratory syncytial virus (RSV) are primary causes of acute respiratory tract infections (ARTIs) in children. New respiratory viruses including human metapneumovirus (hMPV), human bocavirus (hBoV), and influenza 2009 A(H1N1) virus have a strong impact on the pediatric population. To evaluate epidemiological and clinical features of ARTIs in hospitalized children. From December 1, 2008, to December 31, 2009, all children under age fifteen (n = 575) hospitalized for ARTIs were investigated for influenza A (subtype H1N1, H3N2, and 2009 H1N1) and B, RSV A and B, hMPV, and hBoV by PCR. Fifty-one percent of samples were positive for these respiratory viruses. The frequencies of virus detection were RSV 34·1%, hBoV 6·8%, hMPV 5%, seasonal influenza A 5%, and seasonal influenza B 0%. From April 2009, 11·6% of collected samples were influenza 2009 A(H1N1) positive. Respiratory syncytial virus activity peaked in January, hBoV in February, and hMPV in April. Seasonal influenza A was detected only between January and April 2009, while influenza 2009 A(H1N1) peaked in November. Respiratory syncytial virus and hMPV were mainly associated with lower respiratory tract infections (LRTIs) and with necessity of O(2) administration. The 2009 pandemic influenza was more frequently detected in elder children (P < 0·001) and was associated with higher, longer-lasting fevers compared with other viral infections (P < 0·05). All considered viruses were involved in LRTIs. The primary clinical relevance of RSV and a similar involvement of both seasonal influenza and emerging viruses investigated were observed on the pediatric population.
Epidemiological and clinical features of respiratory viral
infections in hospitalized children during the circulation
of inﬂuenza virus A(H1N1) 2009
Department of Pediatrics, Sacco Hospital, University of Milan, Milan, Italy.
Department of Public Health-Microbiology-Virology, University of
Milan, Milan, Italy.
Department of Pediatrics, San Paolo Hospital, University of Milan, Milan, Italy.
Department of Health Sciences, University of
Genoa, Genoa, Italy.
Correspondence: Gianvincenzo Zuccotti, Department of Pediatrics, Sacco Hospital, University of Milan, via GB Grassi 74, 20157 Milan, Italy.
Setting: Two Pediatric Clinics at the University of Study of Milan, in Milan, Italy (‘L. Sacco’ and ‘S. Paolo’ Hospitals); Department of Public Health-
Microbiology-Virology, University of Milan.
Accepted 27 April 2011. Published Online 25 May 2011.
Background Seasonal inﬂuenza viruses and respiratory syncytial
virus (RSV) are primary causes of acute respiratory tract
infections (ARTIs) in children. New respiratory viruses including
human metapneumovirus (hMPV), human bocavirus (hBoV), and
inﬂuenza 2009 A(H1N1) virus have a strong impact on the
Objectives To evaluate epidemiological and clinical features of
ARTIs in hospitalized children.
Methods From December 1, 2008, to December 31, 2009, all
children under age ﬁfteen (n = 575) hospitalized for ARTIs were
investigated for inﬂuenza A (subtype H1N1, H3N2, and 2009
H1N1) and B, RSV A and B, hMPV, and hBoV by PCR.
Results Fifty-one percent of samples were positive for these
respiratory viruses. The frequencies of virus detection were RSV
34Æ1%, hBoV 6Æ8%, hMPV 5%, seasonal inﬂuenza A 5%, and
seasonal inﬂuenza B 0%. From April 2009, 11Æ6% of collected
samples were inﬂuenza 2009 A(H1N1) positive. Respiratory
syncytial virus activity peaked in January, hBoV in February, and
hMPV in April. Seasonal inﬂuenza A was detected only between
January and April 2009, while inﬂuenza 2009 A(H1N1) peaked in
November. Respiratory syncytial virus and hMPV were mainly
associated with lower respiratory tract infections (LRTIs) and with
necessity of O
administration. The 2009 pandemic inﬂuenza was
more frequently detected in elder children (P <0Æ001) and was
associated with higher, longer-lasting fevers compared with other
viral infections (P <0Æ05).
Conclusions All considered viruses were involved in LRTIs. The
primary clinical relevance of RSV and a similar involvement of
both seasonal inﬂuenza and emerging viruses investigated were
observed on the pediatric population.
Keywords Acute respiratory tract infections, emerging viruses,
inﬂuenza virus A(H1N1) 2009, pediatric hospitalizations, viral
Please cite this paper as: Zuccotti et al. (2011) Epidemiological and clinical features of respiratory viral infections in hospitalized children during the circula-
tion of inﬂuenza virus A(H1N1) 2009. Inﬂuenza and Other Respiratory Viruses 5(6), e528–e534.
Acute respiratory tract infections (ARTIs) are associated
with signiﬁcant morbidity worldwide; viruses are by far
the most common causes of ARTIs, especially among
In particular, seasonal inﬂuenza viruses
(type A and B) and respiratory syncytial virus (RSV) are
the main etiological agents during the epidemic period
(between October and April in the northern hemi-
RSV infection is usually much more frequently
identiﬁed than inﬂuenza in children; indeed, about 77%
of infants have had an RSV infection before 5 years of
age. This virus is the main cause of bronchiolitis, which is
one of the major reasons of hospitalization in children
under 2 years of age.
However, recent data show the
important clinical role of seasonal inﬂuenza in children.
In fact, the rate of hospitalization for seasonal inﬂuenza is
not <3Æ6 per 10 000 child ⁄ year, and hospitalization can
also regard previously healthy children and children older
than 2 years.
The recent epidemiological scenario has
e528 ª 2011 Blackwell Publishing Ltd, Inﬂuenza and Other Respiratory Viruses, 5, e528–e534
been enlivened by the identiﬁcation and emergence of sev-
eral pathogens with an airborne transmission pathway
such as human metapneumovirus (hMPV), ﬁrst isolated
human bocavirus (hBoV), discovered in 2005,
and inﬂuenza virus 2009 A(H1N1), identiﬁed in 2009, and
responsible for the ﬁrst pandemic of the new millennium.
HMPV and hBoV are isolated in 3Æ9–16% of children hos-
pitalized for ARTIs. The ﬁrst is associated with a large
spectrum of clinical manifestations that range from mild
upper respiratory tract disease to severe bronchiolitis and
and thus, it is considered to be one of the
most important respiratory emerging viruses, while the
second seems to have a marginal role as it causes mainly
upper respiratory tract infections (URTIs), when detected
The 2009 pandemic inﬂuenza affected the pediatric pop-
ulation in 60% of cases
causing a signiﬁcant number of
recovery also in children aged over 5 years. It seems to
cause generally mild disease, similar to those of seasonal
, while severe manifestations seem concentrated
in patients with risk factors.
This study aimed to evaluate the frequency and the
demographic and clinical features of ARTIs caused by
known viruses (i.e., RSV and seasonal inﬂuenza) and newly
identiﬁed viruses (i.e., inﬂuenza 2009 A(H1N1), hMPV,
and hBoV) in children hospitalized for ARTI in Milan
(Italy) from December 2008 to December 2009.
Materials and methods
From December 1, 2008, to December 31, 2009, we
enrolled 575 children aged between 0 and 15 years hospi-
talized for an ARTI in two Pediatric Clinics at the Univer-
sity of Milan (‘L. Sacco’ and ‘S. Paolo’ Hospitals). After
informed consent was obtained from the parents, an oro-
pharyngeal swab (Plain Swabs; Copan, Brescia, Italy) was
collected from each child within 24 hour after hospital
admission and tested at the Department of Public Health-
Microbiology-Virology, University of Milan, using PCR
assays to detect viral respiratory pathogens (i.e., inﬂuenza
type A, subtype H1N1, H3N2, and 2009 H1N1; inﬂuenza
type B; RSV type A and B; hMPV; and hBoV).
A standardized datasheet was used to record socio-
demographic data (age, gender, risk factors) obtained
through parents interview and clinical information (dura-
tion of hospitalization, detailed disease signs and symptoms
before and during hospitalization, prescribed drug therapy)
by medical chart abstraction.
Clinical data interpretation
For this study, children <15 years of age hospitalized with
symptoms of ARTI such as cough, rhinitis, sore throat,
wheezing, panting, dyspnea, or apnea were enrolled.
Patients were assessed and categorized according to diag-
nosis of upper respiratory tract infections, wheezy bronchi-
tis, bronchitis, bronchiolitis, and pneumonia on the basis
of clinical and roentgenographic ﬁndings. The criteria pro-
posed by Ruuskanen and Ogra
were used for deﬁnitions
of bronchiolitis, pneumonia, and wheezy bronchitis.
Acute illnesses indicated as upper respiratory infections
(URTIs) were characterized by cough, rhinorrhea, sore
throat, and ⁄ or otitis media, with normal thoracic objectiv-
ity and X-ray. An acute illness characterized by cough,
rhonchi, and diffuse expiratory wheezing upon thoracic
auscultation was diagnosed as wheezy bronchitis, while a
illness with the same characteristic but without expiratory
wheezing in any phase of its course was diagnosed as bron-
chitis. Bronchiolitis was diagnosed when dyspnea, tachyp-
nea, diffuse small crackles upon thoracic auscultation, and
roentgenographic evidence of hyperinﬂation of the lung
with or without areas of collapse were present in children
younger than 2 years of age. Pneumonia diagnosis was
based on auscultation of pathological breath sounds, such
as small crackles or decrease ⁄ absence of vesicular sound, in
a zone of the chest, and on radiographic ﬁndings of lung
parenchymal involvement with interstitial-alveolar inﬁl-
trates and ⁄ or consolidation.
The term lower respiratory tract infections (LRTIs) was
used to indicate acute illness with the presence of signs of
lower airway involvement (tachypnea, dyspnea, wheezing,
rhonchi, or rales) and ⁄ or a positive chest X-ray, so it
includes bronchitis, wheezy bronchitis, bronchiolitis, and
Nucleic acid extraction and ampliﬁcation
Nucleic acid extraction was conducted using a commercial
L’Etoile, France). For RNA virus detection, cDNA was syn-
thesized with pd(N)6 random hexamer primers (Amersham
Biosciences, Little Chalfont, UK) using an MMLV reverse
transcriptase (Invitrogen Tech-Line, Carlsbad, CA, USA).
Viral detection was performed by PCR assays. To simulta-
neously detect and type seasonal A and B inﬂuenza viruses,
a one-step real-time RT-multiplex-PCR assay was per-
formed using primer ⁄ probe sets for two different genome
regions: the matrix region of inﬂuenza type A virus and
the nucleoprotein region of inﬂuenza type B virus.
enza A-positive samples were subtyped using an RT-multi-
plex-PCR assay with speciﬁc primers for the hemagglutinin
gene of inﬂuenza A ⁄ H1 and A ⁄ H3 viruses.
2009 A(H1N1) inﬂuenza virus was detected using a one-
step real-time RT-PCR, in accordance with the Centers for
Disease Control and Prevention guidelines.
RSV A and
RSV B were identiﬁed by multiplex nested PCR (fusion
gene, 336 and 582 bp, respectively) using speciﬁc primer
Two nested PCR assays were performed to detect a
Respiratory viral infections in children
ª 2011 Blackwell Publishing Ltd, Inﬂuenza and Other Respiratory Viruses, 5, e528–e534 e529
151-bp (nt. 44–195) fragment of the matrix gene of hMPV
and a 354-bp (nt. 2351–2704) fragment of the nucleopro-
tein gene of hBoV,
respectively. Appropriate positive and
negative controls were included in any PCR assay.
Data were expressed as median (interquartile range, IQR)
and percentages (95% conﬁdence intervals, 95% CI) as
appropriate. Comparisons between groups were performed
using the chi-square test or Fisher’s exact test. A
P-value < 0Æ05 was considered statistically signiﬁcant (two-
tailed test). All statistical analyses were performed using
OpenEPI software, version 2.2.1.
From December 2008 to December 2009, 575 children hos-
pitalized for ARTIs (338 boys and 237 girls; median age
9Æ0 months, IQR 3Æ0–24Æ0 months) were enrolled. Twenty-
four children were not enrolled because guardian consent
Children were divided into ﬁve age-groups: <6 months
(n = 242; 42Æ1%, 95% CI: 38Æ1–46Æ2), 6–11 months (n = 77;
13Æ4%, 95% CI: 10Æ8–16Æ4), 12–23 months (n = 106; 18Æ4%,
95% CI: 15Æ4–21Æ8), 2–5 years (n = 99; 17Æ2%, 95% CI: 14Æ3–
20Æ5), and 6–15 years ( n = 51; 8Æ9%, 95% CI: 6Æ7–11Æ4).
Patients were more frequently affected by LRTIs than
URTIs (67Æ8%, 95% CI: 63Æ9–71Æ5 versus 32Æ2%, 95% CI:
28Æ4–36Æ1; P <0Æ0001). Bronchiolitis was diagnosed in 145
children (25Æ2%, 95% CI: 21Æ8–28Æ9), pneumonia in 151
(26Æ3%, 95% CI: 22Æ8–30Æ0), wheezy bronchitis in 57 (9Æ9%,
95% CI: 7Æ7–12Æ6), and bronchitis in 37 (6Æ4%, 95% CI:
Frequency of viral respiratory infections
Molecular investigations revealed viral gene sequences in
293 (51Æ0%, 95% CI: 46Æ9–55Æ0) samples. Respiratory syn-
cytial virus was detected in 196 (34Æ1%, 95% CI: 30Æ3–38Æ0)
of collected samples. Of these, 67 (34Æ2%, 95% CI: 27Æ8–
41Æ0) were RSV A positive and 129 (65Æ8%, 95% CI: 59Æ0–
72Æ2) were RSV B positive (P <0Æ05). HBoV was detected
in 39 (6Æ8%, 95% CI: 5Æ0–9Æ1) and hMPV and seasonal
inﬂuenza A in 29 (5Æ0%, 95% CI: 3Æ5–7Æ1) samples. Regard-
ing seasonal inﬂuenza A-positive samples, 25 (86Æ2%, 95%
CI: 70Æ0–95Æ5) were subtype H3 and 4 (13Æ8%, 95% CI:
4Æ5–30Æ0) were subtype H1 (P <0Æ05). No inﬂuenza B virus
cases were identiﬁed.
From April 2009 to December 2009, 224 samples were
also tested for 2009 A(H1N1) viral sequences: 26 (11Æ6%,
95% CI: 7Æ9–16Æ3%) were 2009 A(H1N1) positive.
Mixed infections were detected in 8Æ2% of ARTIs
Table 1), and in particular, in 41Æ0% of samples positive
for hBoV, 9Æ2% of samples positive for RSV, and 7Æ7% of
samples positive for inﬂuenza 2009 A(H1N1) (hBoV co-
infections versus RSV and inﬂuenza 2009 A(H1N1);
P <0Æ003). Single and co-infections were associated with
LRTIs with similar percentage (83Æ3% versus 78Æ8%,
Seasonal and age distribution of viral infections
Evidence of viral infections was present throughout the
year and highest in December 2008 (81 positive of 99 sam-
ples) and in January 2009 (74 ⁄ 104). Virus detection fell
steeply from March (30 ⁄ 61) to May (5 ⁄ 15) and further in
June (3 ⁄ 5). No viruses were detected in July and August
(0 ⁄ 7). A sharp rise in viral identiﬁcation was observed
between October and November (20 ⁄ 92), when inﬂuenza
2009 A(H1N1) peaked in Italy. The frequency of viral
infection was higher in December 2008 than in December
2009 (81 ⁄ 99 versus 22 ⁄ 40; P <0Æ05). The epidemic peaks
of RSV (type A and B), hBoV, and hMPV were observed
in January, February, and April, respectively. Seasonal
inﬂuenza A ⁄ H1N1 and inﬂuenza A ⁄ H3N2 were detected
only between December 2008 and April 2009, while their
circulation was not registered in autumn or winter 2009.
Inﬂuenza 2009 A(H1N1) was ﬁrst detected in September
and then peaked in November 2009 (
Viral infections were detected more frequently in chil-
dren younger than 24 months of age (84Æ3% versus 15Æ7%,
P <0Æ05). Respiratory syncytial virus (type A and B)
accounted for 59Æ5% of infections in children younger than
6 months, while elder children experienced seasonal inﬂu-
enza, hBoV, RSV, and hMPV infections with similar fre-
The median age of children with a 2009 A(H1N1)
inﬂuenza was signiﬁcantly higher than that of children
infected with the other viruses (median age: RSV: 3 months,
Table 1. Co-infections in positive samples
Viruses detected No. of cases Diagnosis
RSV B-Inﬂuenza A 5 2 URTI, 3 pneumonia
RSV A-hBoV 3 1 pneumonia,
2 wheezy bronchitis
RSV B-hBoV 5 2 pneumonia,
Inﬂuenza A-hBoV 2 2 URTI
Inﬂuenza A-RSV A-hBoV 2 2 bronchiolitis
RSV B-hMPV 3 1 bronchiolitis,
2 wheezy bronchitis
Inﬂuenza A(H1N1)2009-hBoV 2 2 pneumonia
hMPV–hBoV 2 2 bronchiolitis
hBoV, human bocavirus; hMPV, human metapneumovirus; RSV,
Respiratory syncytial virus; URTI, upper respiratory tract infections.
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hMPV: 6 months, hBoV: 10 months, seasonal inﬂuenza
A: 15 months, 2009 A(H1N1) inﬂuenza: 27 months, P <
Socio-demographic and clinical features of chil-
dren with viral respiratory infection
For analysis of the demographic and clinical features of
children with viral respiratory infection, co-infected
patients were excluded. Respiratory syncytial virus A and B
were considered together because their clinical and socio-
demographic features did not differ signiﬁcantly (P >0Æ05).
Fever was present in all patients, except approximately
one-third of RSV-infected children. The average duration
of fever was signiﬁcantly longer in children with 2009 pan-
demic inﬂuenza than in RSV-positive or hMPV-positive
children (4 Æ9 versus 3Æ 6 and 2Æ8 days, respectively,
P <0Æ05); 70Æ8% of children with 2009 pandemic inﬂuenza
had high fever (‡39C) (
Cough and rhinitis were less associated with seasonal
inﬂuenza than with other infections (Table 2). Dyspnea,
hypoxia, and the resulting necessity of O
were signiﬁcantly associated with RSV (P <0Æ05). The 2009
A(H1N1) inﬂuenza-positive and hMPV-positive children
had feeding difﬁculties compared with children with the
other infections (hMPV: 100%; inﬂuenza 2009 A(H1N1):
87Æ5%; RSV: 68Æ0%; hBoV: 56Æ5%; seasonal inﬂuenza A:
50Æ0%; P <0Æ05) and received antibiotics more frequently
than RSV-positive children (hMPV: 100%; inﬂuenza 2009
A(H1N1): 100%; RSV: 79Æ8%; P <0Æ05). No patients
required intensive care (Table 2).
All viruses considered in this study were involved in
LRTIs with different frequencies. Lower respiratory tract
infections were associated with 91Æ6% of RSV, 66Æ6% of
hMPV, 56Æ5% of hBoV, 50Æ0% of seasonal inﬂuenza A, and
41Æ7% of 2009 A(H1N1) inﬂuenza infections (RSV-LRTI
versus other viruses-LRTI, P <0Æ05), (Table 2). In particu-
lar, bronchiolitis was more frequently associated with RSV
than with hMPV or hBoV infections (55Æ6% bronchiolitis-
RSV versus 20% bronchiolitis-hMPV and 8Æ7% bronchioli-
tis-hBoV, P <0Æ05). No cases of bronchiolitis were
observed in association with seasonal or 2009 pandemic
RSV-positive and hMPV-positive patients required use
of bronchodilators more frequently than children infected
by the other viruses (RSV: 84Æ8%; hMPV: 79Æ2%; hBoV:
43Æ5%; inﬂuenza A: 35Æ0%; 2009 A(H1N1) inﬂuenza:
37Æ5%; P <0Æ05) (Table 2). No inﬂuenza antivirals were
administered to any patient during the study period.
The main risk factors for ARTIs observed in patients
with a viral infection were exposure to environmental
tobacco smoke (25Æ3%), family history of atopic disease
(23Æ9%), and the presence of at least one sibling (15Æ3%)
This report describes the frequencies, the demographic fea-
tures, and the clinical features of viral infections identiﬁed
following surveillance for ARTIs in children hospitalized
for ARTI in Milan (Italy) from December 2008 to Decem-
Fifty-one percent of children hospitalized for ARTIs had
an infection caused by either known viruses (i.e., RSV and
seasonal inﬂuenza) or newly identiﬁed viruses (i.e., 2009
A(H1N1) inﬂuenza, hMPV, and hBoV). Probably, most of
samples that resulted negative for the considered viruses
could have been positive for other viruses not included in
this study, such as parainﬂuenza viruses, coronaviruses,
adenoviruses, and rhinoviruses.
The data revealed that children younger than 2 years of
age, particularly boys, were at high risk of hospitalization
for ARTIs compared with older patients.
Respiratory syncytial virus was the main agent associated
with ARTI in children, especially in patients younger than
Number of patients
Figure 1. Monthly distribution of detected respiratory viruses in
children hospitalized for respiratory tract infections between December
2008 and December 2009.
age < 6 6 ≤ age < 12 12 ≤ age < 24
24 ≤ age < 60 age ≥ 60
Figure 2. Age-group distribution of detected viruses in children
hospitalized for respiratory tract infections.
Respiratory viral infections in children
ª 2011 Blackwell Publishing Ltd, Inﬂuenza and Other Respiratory Viruses, 5, e528–e534 e531
6 months, and was responsible for almost all LRTIs. The
primary clinical relevance of RSV in children is well charac-
terized. Serologic evidence indicates that nearly all children
have been infected by RSV within the ﬁrst 2 years of life.
Hospitalization is required in approximately 0Æ5–2% of
cases and 80% of these occur in the ﬁrst year of life.
Europe, RSV accounts for 42–45% of hospital admission
for LRTIs in children younger than 2 years; in particular,
in studies on hospitalized children, RSV is associated with
bronchiolitis in 60–90% of cases and with pneumonia in
25–50% of cases.
No vaccines against this virus are avail-
able so far, but prophylaxis with palivizumab (a human,
Table 2. Socio-demographic and clinical characteristics in children hospitalized for a single viral respiratory infection
n = 178
n =24 P-value
Male ⁄ female ratio 1Æ51Æ80Æ75 0Æ71Æ8 P <0Æ001
Median age (months) 3
IQR (months) 2Æ0–6Æ05Æ0–17Æ03Æ0–19Æ012Æ0–30Æ08Æ0–57Æ5
No. of children in household ‡3 (%) 27 (15Æ2)
4 (17Æ4) 9 (37Æ5)
Passive smoking (%) 45 (25Æ3) 8 (34Æ8) 5 (20Æ8) 7 (35Æ0) 9 (37Æ5)
(%) 3 (1Æ7)
0 (0) 0 (0) 5 (25Æ0) 5 (20Æ8)
Family history of atopic disease
(%) 36 (20Æ2) 10 (43Æ5) 10 (41Æ7) 2 (10Æ0)
0 (0) 0 (0) 0 (0)
Prematurity (<37 weeks) (%) 15 (8Æ4)
2(8Æ7) 5 (20Æ8)
2 (10) 3 (12Æ5) P <0Æ05
Birth weight < 10th percentile (%) 15 (8Æ4)
4 (17Æ4) 5 (20Æ8)
2 (10) 2 (8Æ3) P <0Æ05
Attending of community
(%) 24 (13Æ5)
8 (34Æ8) 5 (20Æ8) 7 (35Æ0) 15 (62Æ5)
Duration of hospitalization mean (days) 5Æ64Æ95Æ45Æ35Æ6
Fever (‡37Æ5C, axillary) (%) 127 (71Æ3)
Duration of fever (days) 3Æ6
High fever (‡39C, axillary) (%) 39 (21Æ9)
13 (56Æ5) 14 (58Æ3) 7 (35Æ0)
Cough (%) 178 (100)
21 (91Æ3) 24 (100)
22 (91Æ7) P <0Æ05
Duration of cough (days) 8Æ06Æ36Æ27Æ57Æ0
Rhinitis (%) 178 (100)
Duration of rhinitis (days) 8Æ87Æ26Æ66Æ77Æ0
(%) 63 (35Æ4)
6 (26Æ1) 5 (20Æ8) 2 (10Æ0)
5 (20Æ8) P <0Æ05
< 95% in aria) (%) 45 (25Æ3)
Feeding difﬁculties (%) 121(68Æ0)
URTI (%) 15 (8Æ4)
Bronchiolitis (%) 99 (55Æ6)
Pneumonia (%) 39 (21Æ9) 4 (17Æ4) 7 (29Æ2) 5 (25Æ0) 5 (20Æ8)
Wheezy bronchitis (%) 17 (9Æ6) 5 (21Æ7) 2 (8Æ3) 2 (10Æ0) 3 (12Æ5)
Bronchitis (%) 8 (4Æ5) 2 (8Æ7) 2 (8Æ 3) 3 (15Æ0) 2 (8Æ4)
(%) 51 (28Æ6)
Corticosteroids (%) 124 (69Æ7) 10 (43Æ5) 14 (58Æ3) 7 (35Æ0) 14 (58Æ3)
Bronchodilators (%) 151 (84Æ8)
Antibiotics (%) 142 (79Æ8)
21 (91Æ3) 24 (100)
17 (85Æ0) 24 (100)
IQR, interquartile range; RSV, Respiratory syncytial virus; URTI, upper respiratory tract infections.
Chi-square test or Fisher’s exact test or Student’s t-test.
Asthma, atopic dermatitis, allergic rhinitis, or anaphylaxis.
Asthma, atopic dermatitis, allergic rhinitis, or anaphylaxis in ﬁrst-degree relatives.
Pulmonary, cardiac, or neurological diseases, chronic kidney insufﬁciency, or immunodeﬁciency
Attending day nursery or school.
Conditions characterized by tachypnea, use of accessory respiratory muscles, presence of costal retraction, nasal ﬂare, and grunting.
Criteria to supplement oxygen were <92% oxygen saturation or severe tachypnea.
Different primes (
) between groups mean a statistically signiﬁcant difference.
e532 ª 2011 Blackwell Publishing Ltd, Inﬂuenza and Other Respiratory Viruses, 5, e528–e534
mouse monoclonal antibody directed against the F protein
of RSV) is available for vulnerable infants, in whom the
course of RSV infection could be worse, with a 1–5% mor-
The two most important studies on RSV epidemiology
in Italy have shown that the epidemic starts in October–
November and ends in April–May, with peak incidence in
In this study, RSV activity peaked in Janu-
ary; however, in contrast with previous studies, it rose
gradually from October 2009.
Seasonal inﬂuenza viruses were identiﬁed in 5% of sam-
ples and between December 2008 and April 2009 only. No
inﬂuenza B viruses were detected during the study period.
The absence of seasonal inﬂuenza viruses at the end of
2009 in our study is in agreement with data from both the
Italian Inﬂuenza Surveillance Network (INFLUNET)
the European Centre for Disease Prevention and Control.
In this study, hMPV was detected in 5% of patients.
These data are in agreement with published literature, in
which frequencies of hMPV infections ranged from 3Æ9%
to 16%. Some authors have claimed a clinical similarity
between hMPV and RSV infections.
In the population
analyzed, hMPV was associated with LRTIs, dyspnea, and
hypoxia less frequently than RSV.
HBoV infection was involved in 6% of ARTIs and in
41% of all co-infections identiﬁed. These data are in agree-
ment with studies investigating hBoV infection in ARTIs,
which have found a prevalence of 1Æ5–18Æ3%,
42Æ5% mean percentage of co-infections with other viral
In most cases, hBoV had a marginal clinical
importance when identiﬁed alone, causing an URTI in
43Æ5% and requiring oxygen in 8Æ 7% of cases. However,
according to other studies, this study raises the possibility
that hBoV is also associated with severe ARTIs such as
The seasonal peak of hBoV varies among studies, but
is usually described in the early winter.
In this study,
hBoV peak was observed in February, and its circulation
was low at the end of 2009. In agreement with data regis-
tered in European countries,
the present study dem-
onstrates that the 2009 pandemic inﬂuenza virus peaked in
November 2009; In agreement with published litera-
our data indicate that children with high hospital-
ization risk for pandemic inﬂuenza were not only those
younger than 2 years of age or with chronic disease (as
usually observed for seasonal inﬂuenza), but also children
older than 5 years of age, accounting for more of 25% of
recovery from 2009 pandemic inﬂuenza. Finally, 2009 pan-
demic inﬂuenza caused a clinical manifestation similar to
seasonal inﬂuenza with mild severity, although these chil-
dren had bad general conditions because of fever.
In conclusion, all viruses considered in this study circu-
lated in Italy and were involved in LRTIs in children. These
ﬁndings conﬁrm the primary clinical relevance of RSV, and
a similar involvement of both the seasonal inﬂuenza and
the emerging viruses investigated in ARTIs among hospital-
Funding: This research was supported by MIUR (Ministry
of Education, University and Research); Grant numbers:
2005067255_003 and 2007 LPAF42_003. Competing inter-
ests: None declared. Ethical approval: Luigi Sacco Hospital
Study concept and design: G Zuccotti, E Tanzi, M Giovan-
nini, E Riva, A Amendola. Acquisition of data: D Dilillo,
E Galli, F Salvini. Analysis and interpretation of data: A Zap-
pa, M Martinelli, E Galli, A Amendola, E Pariani. Drafting of
the manuscript: E Galli, A Zappa. Critical revision of the
manuscript for important intellectual content: D Dilillo,
A Amendola, A Zappa. Statistical analysis: E Galli, A Zappa,
M Martinelli. Final approval of the version to be published:
G Zuccotti, E Tanzi, M Giovannini, E Riva.
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