Which of the following illnesses is not caused by a virus?

Strep throat is an illness caused by bacteria, specifically Streptococcus pyogenes, rather than a virus. This distinction is important in understanding the treatment options and the nature of the illness. Bacterial infections like strep throat can be effectively treated with antibiotics, which do not work on viral infections. In contrast, the flu, common cold, and COVID-19 are all viral illnesses, requiring different approaches to management and care. Understanding the difference between bacterial and viral infections is crucial for proper diagnosis and treatment in the field of nail technology and overall healthcare.