Colds are generally caused by viruses, but can also be secondary to bacterial infections, both of which can cause fever; other infections, blood disorders, connective tissue diseases, etc., can also cause fever. Colds are a type of upper respiratory infection, caused by viruses, but can be secondary to bacterial infections; both may have symptoms of fever, and you cannot distinguish between the two on the basis of fever. Viral colds usually have a normal or low white blood cell count with an elevated lymphocyte ratio; if routine blood tests reveal an increased white blood cell count and neutrophils, this suggests a bacterial infection. Fever can also be seen in other systemic infections, blood disorders, connective tissue disorders, intracranial lesions, etc. It is necessary to go to the appropriate specialist to clarify the cause of the disease before treatment.