Since an outbreak of COVID-19 was detected among the crew and passengers of the Diamond Princess cruise ship in early 2020, the total number of cases of SARS-CoV-2 has surpassed 440,000 in Japan. However, that number remains small compared with other countries, such as the United States, a few European countries, and China. Despite the Japanese government not imposing a lockdown or implementing large-scale testing at the municipal level, the country has managed to contain the smaller outbreaks. To avoid infection, it is important to wear a face mask, wash one's hands, and observe social distancing. In addition, we focus on the clinical laboratory testing performed using the latest technology to detect SARS-CoV-2 RNA in a hospital in Yokohama, Japan. Large-scale testing of viral RNA would be useful for detecting asymptomatic virus carriers as is done in other countries, and could be carried out as a future measure for controlling COVID-19.