evidence: Having confirmed that the cultured coronavirus originated from the child, the question remained as to whether this was an isolated clinical case, or whether HCoV-NL63 is circulating in humans. To address this question, we used two diagnostic RT-PCR assays to examine respiratory specimens of hospitalized individuals and those visiting the outpatient clinic between December 2002 and August 2003 (Fig. 2). We identified seven additional individuals carrying HCoV-NL63 (Table 1). Sequence analysis of the PCR products indicated the presence of a few characteristic point mutations in several samples, suggesting that several viruses with different molecular markers may be cocirculating (Fig. 3 and Supplementary Fig. 3 online). At least five of the HCoV-NL63-positive individuals suffered from respiratory tract illness; the clinical data of two individuals was not available. Including the index case, five of the patients were children less than 1 year old, and three patients were adults. Two adults were likely to be immunosuppressed, as one of them was a bone marrow transplant recipient and the other an HIV-positive patient suffering from AIDS, with very low CD4+ cell counts (Table 1). No clinical data was available for the third adult. [...] Table 2 Percent nucleotide sequence identity between HCoV-NL63 and other coronaviruses