Background: Recently, two new polyomaviruses (PyV), termed WUPyV and KlPyV, were identified in respiratory tract specimens from children with acute respiratory tract infections (ARTIs). However, their roles in the disease have not been determined. Objectives: To determine the prevalence of WUPyV and KlPyV in the Chinese Population Suffering from ARTIs in Beijing, China, and to examine their possible role in causing disease. Study design: Nasopharyngeal aspirates, nasal swabs and throat swabs were collected from 415 children and 297 immunocompetent adults with lower ARTIs (LARTIs). The specimens were screened by polymerase chain reaction for the presence of WUPyV, KIPyV, and other common respiratory pathogens. Results: Although none of the adults Sampled were positive for either Virus, WUPy in 10 (2.4%) children and KIPyV was detected in 2 (0.5%)of the children sampled, respectively. Eleven of the positive cases were co-detected with either rhinovirus (6/11), respiratory syncytial virus (4/11), parainfluenzavirus virus (3/11) or Mycoplasma pneumoniae (2/11). Phylogenetic analysis of the WUPyV and KlPyV isolates showed that the nucleotide sequences were homologous to those of previously reported Strains. Conclusions: The presence of WUPyV and KlPyV in samples from children but not from immunocompetent adults Suffering from LARTIs Suggests that these viruses primarily infect the young population. Co-detection of additional respiratory pathogens in most of the specimens containing either WUPyV or KlPyV suggests that these viruses do not cause disease independently. (C) 2008 Elsevier B.V. All rights reserved.