New Respiratory Viruses and the Elderly

Jartti, Laura; Langen, Henriikka; Söderlund-Venermo, Maria; Vuorinen, Tytti; Ruuskanen, Olli; Jartti, Tuomas

The interpretation of positive PCR results is complicated by multiple co-existing viruses especially in symptomatic children (up to 43%) and by high virus detection rates in asymptomatic subjects (up to 40-68% in young children) [139, [154] [155] [156] [157] . In a review of the literature that goes back to 1965 and stretches to 2008, the prevalence of viruses in 15000 samples from asymptomatic subjects was higher by PCR than by conventional methods [158] . This casts some doubt on the clinical significance of PCR-positive viral findings overall. Several studies have, on the other hand, demonstrated that positive PCR results are clinically relevant at least as far as HRV is concerned. Identification of HRV correlates with respiratory symptoms, dual HRV infections are rare and overall, the prevalence of recurrent or persistent respiratory viral infections (excluding TTV and HBoV) is low (3-4%) [96, [158] [159] [160] . Positive findings with PCR correlate with systemic or local immune responses in children and in adults [161] [162] [163] . These findings, which mainly apply to HRV and not to HBoV, suggest that HRV-PCR positivity probably reflects a true, current respiratory infection with or without symptoms, rather than residual nucleic acids from some other distant infection. Of course, any findings in upper airway samples do not necessarily reflect the situation in lower airways [164] . Multiple PCR analyses of single samples (multiplex PCR) may sound attractive, but the sensitivity for identification of individual viruses may be lost compared to single virus PCR [165] . Of note, most of these data are from studies on children and adults, and data on new respiratory viruses in the elderly are scarce.