Discussion
fever, infections, infection, nonrespiratory infections, sepsis, nonrespiratory infection
ACUTE RESPIRATORY INFECTIONS, VIRAL INFECTION, INFECTIONS, INFECTION, ACUTE RESPIRATORY INFECTION, HERPES ZOSTER, SEPSIS
In Japan, COVID-19 is diagnosed mainly by pathogenic genetic testing or antigen testing. Since genetic testing is more sensitive than antigen testing, pathogenic genetic testing is widely used for a definitive diagnosis of COVID-19 in Japan [MDW generated by DxH 900, which was evaluated in this study, is a new cytometric parameter that reflects the changes in the monocyte cell volume caused by the activation of monocytes. The result is obtained in approximately one minute with routine CBC and WBC differential testing without the need for ordering additional tests. MDW values may be easily confirmed as a routine clinical examination. Therefore, MDW may be considered a promising screening test parameter for COVID-19 if its diagnostic performance for COVID-19 is superior.Originally, monocytes played an important role in the innate immune system against infection and are believed to be involved in phagocytosis, antigen presentation, cytokine production, and activation of the acquired immune system. Additionally, activation of monocytes is considered to result in the expression of various functions and the diversity of morphology [In addition, Ognibene et al. [In a multivariate analysis of the parameters affecting MDW, it was found that age was not related to MDW but that MDW levels were strongly associated with COVID-19. Lin et al. [In the diagnosis of outpatients with fever, it is necessary to differentiate COVID-19 patients from non-COVID-19 patients with acute respiratory infection. We compared non-COVID-19 with acute respiratory infection by severity. The MDW in each severity was significantly higher in the COVID-19 group compared with the patients with acute respiratory infection in the non-COVID-19 group. These results suggest that COVID-19 is associated with more substantial morphological diversity of monocytes than non-COVID-19 patients with acute respiratory infection, suggesting that SARS-CoV-2 has a higher ability to activate cytokine production and adaptive immunity. Furthermore, COVID-19 and CRP were found to be independent factors associated with MDW, suggesting that MDW (cut-off value: 21.3) may be used as a screening test for COVID-19 in fever outpatients.On the other hand, some patients with nonrespiratory infections also showed increased MDW values. This may be attributable to the fact that many severe patients were included in the nonrespiratory infection group because CRP was high. It is interesting that increased MDW values were observed in one patient with generalized herpes zoster, which is a viral infection. Since MDW is not a specific marker for COVID-19, it should be noted that MDW also increases in severe infections such as sepsis.The limitation of this study was that the age of COVID-19 patients was younger than that of non-COVID-19 acute respiratory infections. Agnello et al. [