Mixed Respiratory Viral Infections in Children with Adenoviral Infections

Human adenoviruses are a common cause of diseases. While epidemic diseases caused by adenoviruses were observed throughout the first half of the 20th century, the viruses were first noted in explant cultures of human adenoidal surgical specimens in 1953; this finding, plus the observation of their apparent general affinity for lymphatic tissue, led to naming designation [1, 2]. More than 50 serotypes grouped into eight species have been defined according to antigenic variability in the surface proteins of the virion. The species differ in their tissue tropism and target organs, causing distinct clinical infections. The most prevalent types in recent surveillance studies are human adenovirus types 3, 2, 1, and 5 [3]. Adenoviral infections cause a wide spectrum of diseases. Adenoviral infections account for 2 to 5% of all respiratory illnesses, and are esti mated to be responsible for 2 to 35% of respiratory viral illnesses in children [2]. Adenoviruses spread by respiratory and fecal-oral routes, and are frequently isolated from the conjunc tiva, throat, and stool. Adenoviral infections are diagnosed by iso lation of virus in tissue culture, direct antigen detection assay, or by DNA polymerase chain reaction (PCR). Molecular techniques, such as PCR, offer rapid, sensitive, and specific diagnosis of adenoviral infections and are becoming the gold standard for diagnosis. A real-time PCR assay for the qualitative detection of all 57 adenovirus serotypes with high sensitivity and specificity in a variety of clinical samples is also available. Moreover, the expanded use of direct fluorescent assays and multiplex PCR assay enables identification of multiple co-infecting viruses and bacteria. Investigators are discovering the common prevalence of adenovirus coinfections with multiple serotypes, other viruses and bacteria [2]. Respiratory viral co-infections, defined as the presence of more than one viral pathogen in the same sample are detected in up to 30% of children with acute respiratory tract infections [4]. The clinical significance and the mechanisms of disease virulence in respiratory viral coinfections remain uncertain. Recent systematic reviews and meta-analyses revealed no significant differences between children with single respiratory virus infection and those with viral-viral coinfection with respect to the length of hospital stay, admission to the intensive care unit, need for mechanical ventilation, oxygen require-