Human Bocavirus in Very Young Infants Hospitalized with Acute Respiratory Infection in Northeast Brazil

Abstract

A cross-sectional study was carried out over a period of 12 months to investigate the occurrence of human bocavirus (HBoV) infection in infants hospitalized for respiratory infections in a teaching hospital in Salvador, Brazil, and to describe the clinical manifestations of this infection. Nasopharyngeal aspirates were collected from the children and immunofluorescence and polymerase chain reaction were performed to investigate the presence of respiratory viruses. HBoV was detected in 4 out of 66 patients. Two of the HBoV-positive infants were co-infected with other viruses. The principal clinical findings in HBoV-positive children were: nasal obstruction, catarrh, cough, fever and dyspnea. This study revealed HBoV infection in children aged <2 months, suggesting that the infection may occur at a very early age.

Introduction

Human bocavirus (HBoV) was first identified in 2005 in Swedish children with acute respiratory infection (ARI) [1]. Since then, HBoV has been found in 1.5–17% of patients with respiratory infections in various countries [1–12]. The occurrence of HBoV infection in infants aged <6 months appears to be low [1, 3, 12, 13]. This study investigated the occurrence of HBoV infection in infants aged <7 months hospitalized with ARI.

Methods

This was a cross-sectional study carried out over a 12-month period between 31 March 2006 and 31 March 2007. Children under 7 months of age, who were hospitalized at the Professor Hosannah de Oliveira pediatric hospital in Salvador, Brazil with a diagnosis of respiratory infection, were included. A questionnaire was applied to collect clinical data and laboratory results. Nasopharyngeal aspirate (NPA) was collected to investigate respiratory viruses. The presence of adenovirus, respiratory syncytial virus (RSV), influenza viruses and parainfluenza viruses was investigated by indirect immunofluorescence (IIF) using a commercially available kit (Chemicon® Temecula, CA, USA). The presence of HBoV and human rhinoviruses (HRVs) was investigated using polymerase chain reaction (PCR). DNA extraction was performed in the NPA using a commercial kit (Wizard® Genomic DNA Purification Kit, Promega® Madison, WI, USA), and RNA extraction was carried out using Trizol® (Invitrogen® Carlsbad, CA, USA). HBoV was detected by PCR using the product of DNA extraction.

Results

During the study period, NPA from 66 children was tested for respiratory viruses using IIF and PCR. Forty children (60.6%) tested positive for at least one agent. Twenty-nine children (43.9%) tested positive for one virus, 10 (15.2%) for two and 1 (1.5%) for three different viruses. HRV (24 cases) and RSV (14 cases) were the viruses most frequently detected. Four children (6.1%) tested positive for HBoV, two of whom were found to be simultaneously infected with other viruses: RSV and enterovirus in one case, and HRV in the other. Their ages ranged from 43 to 191 days. All four children had nasal obstruction and rhonchi, while three had productive coughs, dyspnea, fever and chest indrawing and rales at lung auscultation. Two patients had acute diarrhea. A summary of clinical data and laboratory results is shown in Table 1.

Table 1.

Clinical data and laboratory results of four hospitalized infants with respiratory infection and positive test for HBoV by PCR

Characteristic	Case 1	Case 2	Case 3	Case 4
Sex	Female	Female	Male	Male
Age (days)	191	43	54	150
Month and year of hospitalization	May/2006	May/2006	July/2006	August/2006
Birth weight (g)	3700	1480	2730	2630
Clinical diagnosis at admission	Bronchiolits	ARIa	Bronchiolits	Pneumonia
Duration of symptoms before hospitalization (days)	3	1	12	9
Signs/symptoms
Rhinorrhea	Yes	Yes	No	Yes
Nasal obstruction	Yes	Yes	Yes	Yes
Cough	Yes	No	Yes	Yes
Fever	Yes	No	Yes	Yes
Cyanosis	No	No	No	No
Chest wall retraction	Yes	No	Yes	Yes
Rales	Yes	No	Yes	Yes
Wheezing	Yes	No	Yes	Yes
Dyspnea	Yes	No	Yes	Yes
Diarrhea	Yes	No	No	Yes
Highest temperature during hospitalization (°C)	38	37	37.5	38.3
Respiratory rate at hospitalization, breaths/min	56	54	78	60
Maximal respiratory rate, breaths/min	68	86	78	60
Chest X-ray	Normal	Normal	Normal	Intersticial infiltrate and atelectasis
Antibiotic treatment before hospitalization	Yes	No	No	Yes
Antibiotic treatment during hospitalization	No	No	Yes	Yes
Length of oxygen therapy (days)	2	No	No	2
Viral coinfection	Yesa	Yesb	No	No
Leukocytes count (cells/mm3)	13 200	7400	11 100	19 800
Blood culture	Not done	Negative	Negative	Not done
Erythrocyte sedimentation rate (mm/h)	42	35	42	21
C-reative protein (mg/l)	Not done	<6	<6	>6
Hospitalization duration (days)	9	9	4	5

^aCo-infection with RSV and enterovirus.

^bCo-infection with rhinovirus.

ARI, Acute Respiratory Infection.

Discussion

The frequency of HBoV in infants with ARI in the present study is in agreement with findings reported from various other studies [1–11]. Two children were <2 months of age, suggesting that the infection may occur at a very early age. Clinical findings in children with HBoV in this study were very similar to those previously described [3–7]. This study was carried out in hospitalized children; hence presumably more severely ill patients were evaluated. However, only one HBoV-positive patient had radiological findings consistent with pneumonia. In this study, two of the four children with HBoV infection had diarrhea. It is possible that HBoV infection may involve both the respiratory and gastrointestinal tracts [14, 15]. In spite of the limited sample size, the present study highlights the fact that HBoV may be present in very young infants hospitalized with ARI.

Funding

Brazilian Ministry of Health; The National Council for Scientific and Technological Development and the Foundation for the Support of Research in the State of São Paulo.