A patient presents to a clinic with sustained high fever ( 39^ C to 40^ C ), weakness, stomach pain, constipation, headache, and loss of appetite. Identify the biological category of the causative agent and the standard diagnostic test used to confirm this disease.

Step-by-step solution

The clinical symptoms described (sustained high fever of 39^ C to 40^ C , weakness, stomach pain, constipation, headache, and loss of appetite) are the classic symptoms of Typhoid fever. Typhoid is caused by the pathogenic bacterium Salmonella typhi. The standard confirmatory diagnostic test for Typhoid is the Widal test. Therefore, the causative agent belongs to the category of Bacteria, and the correct test is the Widal test. ELISA is widely used for viral infections like HIV, while blood smears are typically use