Correlation of viral load as determined by real-time RT-PCR and clinical characteristics of respiratory syncytial virus lower respiratory tract infections in early infancy
Introduction
Respiratory syncytial virus (RSV) is the major viral pathogen of the respiratory tract in early infancy and, due to its frequent involvement of the lower respiratory tract, is recognized as the single most important cause of infant hospitalization (Boyce et al., 2000, Leader and Kohlhase, 2002). Following the use of quantitative reverse transcription (RT)-PCR (Campanini et al., 2007, Falsey et al., 2003), in recent years, real-time RT-PCR has become the method of choice for quantification of RSV load in nasopharyngeal aspirates (NPAs) taken during acute respiratory tract infections (RTI) (Perkins et al., 2005).
In this study, by using a real-time RT-PCR approach, quantification of RSV load in NPAs from 47 infants admitted to hospital with a lower RTI was investigated with respect to: (i) duration of hospitalization; (ii) drop in viral load during patient follow-up and symptom resolution; (iii) RSV subgroups (A and B); (iv) patient subdivision into two groups: one, including patients with bronchiolitis (n = 18), and the other one including patients with lower RTI other than bronchiolitis (n = 27). Viral load in the two subgroups was analysed with respect to patient age, duration of symptoms and RSV subgroup.
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Patients and methods
On the whole, 47 infants with a median age of 5 (1–27) months, admitted to the hospital with a diagnosis of lower RTI in the period November 2006–May 2007, were examined in NPA by real-time RT-PCR for RSV RNA quantification, according to two reported protocols for RSV (subgroups A and B) quantification (Perkins et al., 2005). The intra-assay coefficient of variation (CV) for real-time RT-PCR was 8.53% for RSV-A and 9.39% for RSV-B, while the inter-assay CV was 35.8% for RSV-A, and 31.5% for
Results
The duration of hospitalization was found to be comparable (p = ns) in infants with bronchiolitis versus infants with a lower RTI other than bronchiolitis [8 (4–11) vs. 7 (2–16) days]. In addition, hospitalization was not different (p = ns) in infants with RSV-A infection versus infants with RSV-B infection [8 (3–11) vs. 8 (2–16) days], as well as in young patients with coinfection versus patients with a single RSV infection [9 (6–11) vs. 8 (2–16) days] (Table 1). Drop in viral load was significant
Conclusions
Potential limitations to our study were the following: (1) NPAs were not always taken at the peak of acute RTI; (2) often patients were given therapy before hospitalization, especially steroids and bronchodilators, which can interfere with clinical presentation of infection and/or with virus replication; (3) it was not possible to perform a correct follow-up for all patients after discharge.
However, as a result of our study, the following conclusions can be drawn: (1) RSV viral load decreased
Acknowledgements
We thank all the technical staff of the Servizio di Virologia for performing all the assays. We also are grateful to Daniela Sartori for preparing the manuscript, and to Laurene Kelly for revision of the English. This work was partially supported by the Ministero della Salute, Ricerca Finalizzata Fondazione IRCCS Policlinico San Matteo, grants 89282(05)/A and 89288(05).
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