RSV is recognized as the leading cause of respiratory tract illness in children and is a major nosocomial pathogen. We evaluated RSV genetic variability in nasopharyngeal aspirate samples taken from children with nosocomial and community-acquired RSV infections at a large hospital in southern Brazil during 2010. The patients with nosocomial RSV infection were characterized by prolonged hospital stays and increased mortality (Table 1). Increased risk of severe RSV infection is usually associated with clinical conditions such as prematurity, chronic lung disease, congenital heart disease, and immunosuppression [1, 14]. These same conditions are common among children with prolonged hospital stays .
RSV-A was the predominant group in both nosocomial (15/21 or 71.43%) and community-acquired (30/42 or 71.43%) infections. Only three cases of RSV-A/B co-infection (4.76%) were observed. In previous RSV studies, co-circulation of groups A and B within the same population has been described during epidemic periods, and with different predominance patterns [12, 22]. There have been reports of co-circulation of the RSV-A and RSV-B groups in different years, including in Brazilian populations; however, most sequences have belonged to the RSV-A group [23–25]. Shifts in predominance of particular circulating RSV groups within a given time interval have also been described [21, 26, 27]. These shifts appear to correlate, at least in part, with G-protein gene variability . However, as we collected samples only during one epidemic period for the present study, considerations about epidemiological patterns are restricted.
Only one RSV-A genotype was found circulating within the study sample. It showed high similarities with the previously identified NA1 genotype isolated from Japan . All RSV-A POA sequences (nosocomial and community-acquired) were grouped with this genotype in a phylogenetic branch which presented a bootstrap value of 82%. The p-distance calculated among these sequences was low, demonstrating homogeneity among samples. This is the first study to describe circulation of the Japanese NA1 genotype in Brazil. One could speculate that the introduction of this genotype to Brazil was probably recent and that it became predominant in the Porto Alegre area. Peret and colleagues have hypothesized that a constant shift in predominant genotypes affects protective immunity, allowing for more efficient virus transmission and pathogenicity. Therefore, new RSV strains can be introduced into a given population, but local factors such as strain-specific immunity will determine which strains will circulate successfully and cause outbreak .
We found only one circulating RSV-B group genotype in southern Brazil during 2010: BA4. This genotype has been previously described . The phylogenetic branch grouped many sequences, and the p-distance also indicated some variability within this phylogenetic group (p-distance = 0.037). However, all RSV-B POA genotypes were grouped with the BA genotypes. The first BA genotype was described in Buenos Aires (Argentina) in 1999, and harbors a 60-nucleotide duplication within the G protein gene . It has also been reported in Europe and Asia [12, 29, 30]. The rapid and worldwide spread of the BA genotype implies that it may have a selective advantage over other circulating strains . However, there may be mutations elsewhere in the genome that confer more efficient replication when compared with other RSV-B genotypes. Indeed, RSV (both RSV-A and RSV-B groups) exhibits rapid evolutionary rates , which might justify the emergence of many different genotypes and variability within genotypes as well. The BA4 genotype has circulated worldwide for years and exhibits a high mutation rate; therefore, many BA4 variants could be generated.
In summary, this study evaluated the genetic diversity of RSV within a patient cohort. To our knowledge, this is the first time that circulation of the RSV-A NA1 genotype has been confirmed in Brazil. In addition, we report circulation of the BA4 genotype during 2010. A better understanding of RSV molecular epidemiology will be essential for development of vaccines and antiviral pharmacotherapy against RSV infection. Currently, palivizumab is recommended as a preventive measure in high-risk settings. Unfortunately, this agent is too costly for use in developing countries . Therefore, the development of an efficient vaccine should remain a high priority in managing RSV infection.