[Bronchiolitis viruses]. / Les virus des bronchiolites aiguës.

In Normandy (France), human respiratory syncytial virus (hRSV) was detected in 64.1% of acute bronchiolitis in hospitalized children, rhinovirus in 26.8%, human metapneumovirus (hMPV) in 7.6%, and parainfluenza virus (PIV) in 3.4%. The viruses causing acute bronchiolitis in the community were hRSV (42%), rhinovirus (19.5%), coronavirus (8%), PIV (3.5%), and hMPV (2.5%). In 53.7% of the cases, hRSV infected infants (86.9%), 53.7% being less than 6 months of age. Of the hRSV cases, 48.2% were detected in November and December and 44.5% in January and February. The hRSV epidemic started the 1st or 2nd week of October but it varied from one year to another and from one region to another. hRSV acute bronchiolitis increased from 261 cases in epidemics from 1999-2003 to 341 cases from 2004-2009. Rhinoviruses gave acute bronchiolitis in 38.4% of cases. A rate of 54.6% of viruses was detected in September and October and 38.5% in March and April. A total of 34.2% of infected infants were under 6 months of age, 37.8% between 6 months and 2 years, and 19.5% were between 2 and 5 years old. hMPV epidemics coincided with hRSV epidemics, but they accounted for one-sixth the number of cases. HMPV infected infants (74%) who were older than those infected with hRSV, and the diagnosis was bronchiolitis (59%) and pneumonia (17%). PIV infections (about 100 cases per year) included PIV3 (62.7%), PIV1 (25.3%), and PIV2 (7.3%). PIV1 infections occurred every 2 years in the fall. PIV3 infections were observed every year during the fall and winter, with peaks of infections in the spring in the years without PIV1. There were acute cases of bronchiolitis in 29.8% of PIV3 infections and 18.3% in PIV1 infections.

[Seasonal flu]. / La grippe saisonnière.

Seasonal flu is caused by influenza viruses A and B. These enveloped viruses have a genome made up of seven or eight RNA fragments. The different subtypes are determined by the nature of the two surface glycoproteins HA and NA. Seasonal flu is an epidemic wintertime illness occurring in temperate climate zones. Its epidemiology is linked to the great variability of the virus in time, necessitating an alert system that detects dominating circulating variants each year and that determines the vaccination composition. Clinical flu symptoms are not sufficiently specific to allow for diagnosis with virological tests. This is especially true during non-epidemic periods as well as in subjects older than 65 and younger than five. Children are especially vulnerable to influenza virus infections. Hospitalization occurs more frequently, the younger the child. In children younger than two years, the infection can be pauci-symptomatic and is sometimes detected from non-respiratory symptoms such as lethargy, convulsions, and dizziness. In all cases of respiratory syndrome compatible with influenza virus infection in hospitalized subjects, virological flu diagnosis is of utmost interest. Several tools are available to allow for direct viral detection in respiratory specimens: cell culture isolation, antigenic detection, RNA molecular detection. Choice of method is based on the characteristics of the test: sensibility, specificity, speed and ease of realization, and cost.

[Human metapneumovirus]. / Métapneumovirus humain.

The human metapneumovirus (hMPV) is a new Pneumovirinae related to the avian metapneumovirus type C. hMPV genome differs from human respiratory syncytial virus (RSV) genome by the gene order and the lack of nonstructural genes. Two genetic sub-groups and four sub-types of hMPV are identified. hMPV infections evolve as regular winter outbreaks which have roughly the same size and overlaping RSV epidemics. Among hospitalized children in Caen, hMPV is detected in 9.7% of the cases after RSV (37%), rhinovirus (18%), influenza virus (14.5%), adenovirus (9%), and parainfluenza virus (5%). Most of hMPV infections are observed in children suffering from bronchiolitis, but the localization to lower respiratory tract and the severity of the disease are less frequent in comparison with RSV infections. hMPV is very difficult to isolate using cell culture. Up to now, the only way for hMPV diagnosis was the TS-CRP assays. But the recent apparition of direct antigenic tests allows us to get a fair, rapid, and economic diagnostic tool.

[Virus and sensitization]. / Virus et sensibilisation.

Respiratory viruses are able to replicate in both the upper and lower respiratory epithelium, thus inducing wheezing. Most clinical studies suggest that wheezing illnesses due to respiratory viruses in early childhood are linked to a risk for asthma. Viruses may induce asthma exacerbations through direct effects on their main target, the respiratory epithelium, as well as via a systemic immune-inflammatory reaction. On other hand, studies have also yielded conflicting results in regard to the ability of viral infection to enhance subsequent allergic responses. Do early viral illnesses cause allergic asthma or viral wheezing episodes serve to reveal children who are already predisposed to this disease on basis of an abnormal lung physiology and/or immune response?

Study of influenza C virus infection in France.

From November 2004 to April 2007, specimens were obtained from 2,281 patients with acute respiratory tract illness in Normandy, France. Eighteen strains of influenza C virus were detected in these samples using a combined tissue culture/RT-PCR diagnostic method. Most patients with influenza C virus infection (13/18) were infants or young children (<2 years of age). The most frequent symptoms were fever and cough, and the clinical presentation of influenza C virus infection was similar to that of other respiratory viruses. Thirteen of the 18 infected patients were hospitalized; 3 presented with a severe lower respiratory infection. The hemagglutinin-esterase (HE) gene of 10 isolates was sequenced to determine the lineages of the circulating influenza C viruses. Phylogenetic analysis revealed that most of the isolated strains had an HE gene belonging to the C/Yamagata/26/81-related lineage. These results show that influenza C virus regularly circulates in Normandy and generally causes a mild upper respiratory infection. Because the differential clinical diagnosis of influenza C virus infection is not always easy, it is important to identify viral strains for both patient management and epidemiological purposes.

[Virology: the contribution of molecular biology in the microbiologic diagnosis of pediatric respiratory diseases]. / Virologie : l'apport de la biologie moléculaire dans le diagnostic microbiologique en pneumopédiatrie.

The conventionnal tools used for virological diagnosis include direct antigen detection by immunofluorescence (IFA) or an immunoenzymatic test (EIA), and viral isolation technique (VIT). In most cases, IFA and EIA have a slightly lower sensitivity than VIT but are also able to detect some VIT-negative samples. Results of several teams using RT-PCR technologies show that the molecular methods detect more positive cases than the conventional tools. Work is under way to expand the number of viruses detected by multiplex RT-PCR and to determine wether newly discovered viruses, such as human metapneumovirus, contribute to burden of paediatric lower respiratory infections. In conclusion, according to requirements of speed, low cost of the methods, and to achieve the highest rate of detection of respiratory viruses, the combined use of IFA and multiplex RT-PCR is today likely to be the best way to improve diagnosis of respiratory illnesses in children.