Usefulness of School Absenteeism Data for Predicting Influenza Outbreaks, United States

and second-round PCR were 94°C for 3 min, followed by 40 cycles of 94°C for 30 s, 55°C for 30 s, and 72°C for 2 min. Expected amplifi cation products were 458 bp (PCR-1) and 304 bp (PCR-2). Using dilutions of a synthetic template corresponding to the target sequence, we estimated the sensitivity of the amplifi cation assay to be <5 copies of target sequence by limiting-dilution assay. Negative (sterile water) and positive controls (synthetic template dilutions) were added systematically to each amplifi cation run. A PCR control intended to check the quality of the nucleic acids extraction procedure was also performed systematically on 4 randomly selected samples of each batch (n = 32); this control was based on the detection of an extremely prevalent DNA virus (Torque Teno virus and related viruses, family Anelloviridae) by using a highly conserved amplifi cation system (3). Among the 576 plasma samples tested, no positive signal was identifi ed for KIs-V DNA after agarose gel electrophoresis of PCR1 and PCR-2. Amplifi cation controls (negative, positive, anelloviruse DNA) confi rmed the validity of these results. Using the PCR detection system adopted by Satoh et al., combined with the extraction of large plasma volumes, we were not able to detect KIs-V DNA in the blood of donors tested, suggesting an uncommon frequency in healthy persons in France. Information related to HEV status or ALT levels were not available here because both parameters are not evaluated for routine blood donor screening in France; HEV seroprevalence studies involving blood donors from northern and southwestern France indicate discrepant results (≈3%–≈52%, IgG), possibly related to serologic assay performances and/or geographic differences (4). The precise identity of KIs-V remains uncertain, but according to its extensive initial characterization, complementary studies probably will confi rm its viral origin. Molecular characterization of new full-length sequences will be needed to investigate the real genetic diversity of KIs-V and to help design optimized molecular detection systems. The implication of KIs-V in human health remains under debate. The original publication highlighted the fact that HEV antibody–positive persons in Japan who had moderately elevated ALT levels at a prevalence of KIs-V infection that is nonnegligible; such fi ndings could suggest a link between the virus and liver dysfunctions. HEV and KIs-V also could share the same route of contamination, i.e., foods (5). Further investigations involving diverse human cohorts need to be undertaken to better understand the natural history of KIs-V in humans.