Impact of molecular diagnostics for the detection of respiratory viruses and clinical value

Traditionally, treatment and prevention of respiratory viral disease has mainly focused on influenza virus infection. The epidemiology, impact and severity of influenza virus infection have been studied extensively and it has been shown that influenza virus infection is associated with significant mortality and morbidity every year. Despite these studies influenza, like other respiratory virus infections is often unjustly considered a relatively harmless infectious disease and treatment as not being necessary. Over the past decades, there has been growing attention towards the role of respiratory viruses, especially in immunocompromised patients. In this thesis we aimed to develop molecular diagnostic techniques feasible for use in a routine laboratory setting, and to evaluate their clinical impact. Moreover, we used these techniques to clarify the role of respiratory viruses in specific patient groups at risk. In this thesis we show that the described molecular diagnostic methods exhibit a significant advantage over the existing conventional diagnostic methods. With the use of these sensitive detection methods we show that respiratory viruses can be detected frequently and are more often involved in serious respiratory tract infection than expected previously. To determine the role of respiratory viruses in immunocompromised patients a retrospective study using the developed molecular techniques was performed in hematological cancer patients with pneumonia. With the use of these molecular diagnostics we found an increasing rate of identification from 19% to 35% compared to the conventional detection techniques. In 21% of the patients respiratory viruses were the only identified pathogen. These results led us to conduct a prospective study in which we examined the frequency and severity of respiratory virus infection in recipients who underwent autologous or allogenic stem cell transplantation. We showed an incidence of viral upper and lower respiratory tract infection of 14% with standard viral culture and with 36% with molecular diagnostics. In addition, we showed that infections with respiratory viruses occurred frequently and were associated with severe lower respiratory tract infection. The mortality associated with respiratory virus infection however was low. Finally, we have used the molecular diagnostic detection methods to evaluate the virus load and shedding during infection. Asthmatics often experience more pronounced symptoms during an upper respiratory tract infection than non asthmatics. In the described study we have studied the role of respiratory viruses, in asthmatic and non asthmatic subjects. We showed that the clearance of virus and maximal viral load were similar in both groups. However, the asthmatic subject experienced significantly more symptoms, mainly associated with the lower respiratory tract. These results indicate that ongoing virus replication is not the explanation for the severity of asthmatic symptoms and that other mechanisms, such as host response, may play a role in the development of symptoms. With future research focused on the precise pathogenicity of the various respiratory viruses and on the host's response will be needed to further address the clinical value and cost-effectiveness of molecular diagnostic techniques for the detection of respiratory viruses