A single‐center comparative analysis of outpatients with and without COVID‐19 in Sapporo, Japan

Abstract This study aimed to investigate the demographic, clinical, and epidemiological statistics of Japanese patients attending a designated outpatient clinic for COVID‐19 in Sapporo, Japan, and contrast the clinical and epidemiological features between those with and without mild COVID‐19. A total of 27 (8.6%) of 315 patients were diagnosed with COVID‐19. They had higher proportions of myalgia, direct contact with a confirmed COVID‐19 patient, and attendance of social gatherings in close confines. We believe that our study makes a significant contribution to the literature because it provides a clinical picture of mild COVID‐19 in the Japanese population, which has not been studied extensively. It can also assist in optimizing the local preventive measures to reduce the transmission of COVID‐19.

TA B L E 1 Demographic, clinical, and epidemiological characteristics of patients with and without coronavirus disease

| DISCUSS ION
Our finding that patients with COVID-19 had a significantly higher proportion of direct contact with confirmed COVID-19 cases and participation in social gatherings in the two weeks before presenting at the clinic was consistent with previous studies. 3,4,8 This may be biologically plausible because the main route of transmission of SARS-CoV-2 is through respiratory droplets. 9 Additionally, our results showed that recent travel to areas with ongoing COVID-19 outbreaks did not differ between the two groups. This may be because only three people had traveled to the endemic areas, and our analysis did not have sufficient statistical power to detect the difference. Moreover, we found that myalgia occurred with a significantly higher frequency among patients with COVID-19 than those without the infection. Several case reports noted that myalgia was one of the most common symptoms in confirmed COVID-19 cases. 10 Other predominant symptoms included fever, cough, and dyspnea.
A meta-analysis assessing the clinical, laboratory, and imaging characteristics and outcomes of patients with COVID-19 in 39 case reports and 19 observational studies reported that the frequency of fever, cough, and dyspnea was 89%, 58%, and 46%, respectively. 10 In this study, the cough frequency was similar, but the frequencies of fever and dyspnea were lower than those reported in the metaanalysis above. This can be attributed to the outpatient setting of this study; therefore, mild cases of COVID-19 may have been more likely to present to our clinic. Notably, our study showed that a total of 30% of the patients with COVID-19 had experienced dysgeusia or anosmia, which was a relatively lower frequency than that in previous reports. 10 The reasons are unclear, but one possible explanation is that we may not have accurately captured the symptoms because we collected data based on the information from a self-reported questionnaire.
This study has several limitations. First, our study has selection bias because this study was conducted in an outpatient clinic, and therefore, we may have missed patients with severe symptoms.
Indeed, we had only one patient who required hospitalization for this disease. Second, there is a possibility of recall bias because information about symptoms two weeks before the clinic visit relied on a self-reported questionnaire. Third, antigen testing using saliva or nasopharyngeal swabs was not used for COVID-19 diagnosis because the test had not been introduced at our institution at the time of data collection. Undoubtedly, more effort should be made to continue capturing a comprehensive clinical picture of COVID-19 patients in Japan. Nonetheless, our findings may be applicable to other clinical settings, such as emergency room, where performing a focused history taking is the cornerstone of diagnosis and treatment.

| CON CLUS ION
In conclusion, to our knowledge, this is the first report describing the clinico-epidemiological characteristics of patients attending a specialized outpatient clinic for COVID-19. More studies from Japan will be needed to contribute to the growing volume of clinical evidence and elucidate the complete clinical spectrum of the disease in the Japanese population.

ACK N OWLED G EM ENTS
We thank all members of the office of infection control and prevention at Teine Keijinkai Medical Center for the support of this study.

CO N FLI C T O F I NTE R E S T
The authors have stated explicitly that there are no conflicts of interest in connection with this article.