Blood tests can identify viral and bacterial infections. The changes in blood work are different in bacterial or viral infections. Bacterial infections usually show increased white blood cells and increased neutrophils, while viral infections show reduced or normal total white blood cells and increased lymphocytes. Therefore, routine blood tests can initially determine bacterial and viral infections. There are exceptions to this rule. Some viral infections can also cause an increase in leukocytes, such as rabies virus. Bacterial infections can also cause a low white blood cell count, such as typhoid or paratyphoid fever.