Background: There is a great need to make a rapid differential clinical diagnosis of COVID-19 among respiratory disease patients and determining the prevalence rate of these diseases among the COVID-19 population. Method: Approximately 522 patients with allergic rhinitis, asthma, COPD, and COVID-19 were analyzed for demographic and clinical features. Radiological features were analyzed only for COVID-19 patients. Results: COPD and asthma were more common among COVID-19 patients than allergic rhinitis. All chest CT scans of COVID-19 patients showed bilateral ground-glass opacity. Fever, dry cough, diarrhea, loss of sense of smell and taste, shortness of breath, and blue lips were significantly higher in all COVID-19 patients compared to COPD, asthma, and allergic rhinitis patients. Conclusion: The presence of clinical symptoms such as fever, dry cough, diarrhea, loss of sense of smell and taste, shortness of breath, and blue lips in COVID-19 patients, can be used for differential diagnosis between COVID-19 patients and other respiratory diseases. Then, the diagnosis can be confirmed by chest CT scan for COVID-19 patients without the need for a nasopharyngeal swab or PCR test, especially in epidemic countries. Allergic rhinitis patients are the least exposed to COVID-19 infection among other respiratory disease patients.