The available literature on human coronaviruses (HCoVs) in Japan is limited to epidemiological studies conducted over a maximum of 1 year. We conducted a 4-year study of HCoVs by analyzing 4,342 respiratory specimens obtained in Yamagata, Japan, between January 2010 and December 2013. A pan-coronavirus reverse transcription-PCR screening assay was performed, and all HCoV-positive specimens were subsequently confirmed by sequencing of the PCR products. We detected in 332 (7.6 z) HCoV strains during the study period, comprising 133 (3.1 z) HCoV-NL63, 83 (1.9 z) HCoV-HKU1, 78 (1.8 z) HCoV-OC43, and 38 (0.9 z) HCoV-229E strains. HCoV detection per year ranged from 3.5 z to 9.7 z. HCoVs were detected mainly in winter, with January (28.5 z) and February (25.3 z) 2011 and December 2012 (14.6 z) being the only months in which HCoV-NL63 detection per month exceeded 10.0 z. HCoV-HKU1 displayed clear biennial peaks in January (18.3 z) and February (10.7 z) 2010 and in February (18.8 z) and March (14.7 z) 2012. The peak detection of HCoV-OC43 was 13.6 z in November 2010, while that of HCoV-229E was 10.8 z in March 2013. Our results indicated that there may be annual variations in the circulation of individual HCoV strains. Further long-term surveillance is necessary to clarify HCoV prevalence and circulation patterns in Japan.

Human coronaviruses (HCoVs) belong to the genus Coronavirus in the family Coronaviridae and include HCoV-229E, HCoV-OC43, and severe acute respiratory syndrome (SARS)-CoV (1). Recently, new HCoVs, such as HCoV-NL63, HCoV-HKU1, and Middle East respiratory syndrome (MERS)-CoV, have also been described (1). Four HCoVs (HCoV-229E, HCoV-OC43, HCoV-NL63, and HCoV-HKU1) are associated with a wide range of respiratory illness, including common colds, and with high morbidity outcomes, such as pneumonia and bronchiolitis (1–3). These four HCoVs are found globally, although the frequency of detection of these HCoVs varies with geographical location (1–20). Poor growth and a lack of cytopathic effects on cell cultures have been major deterrents to HCoV research in the past (1). However, with the development of polymerase chain reaction (PCR) technology, there has been broad and rapid development in the field of coronavirology (1).