The elevation in thermoregulatory set-point means that the previous “normal body temperature” is considered hypothermic, and effector mechanisms kick in. The person who is developing the fever has a cold sensation, and an increase in heart rate, muscle tone and shivering in an attempt to counteract the perceived hypothermia, thereby reaching the new thermoregulatory set-point.

• Influenza-like illness is defined as “fever (temperature of 100°F [37.8°C] or greater) and a cough and/or a sore throat in the absence of a known cause other than influenza.”^[1] Possible causes include respiratory syncytial virus, rhinovirus, adenovirus, parainfluenza viruses, coronaviruses, and metapneumovirus.^[2]

• Mononucleosis-like illness is the triad of fever, pharyngitis, and lymphadenopathy which suggests infectious mononucleosis. Other possible causes include cytomegalovirus (CMV), human herpesvirus 6 (HHV-6), human immunodeficiency virus (HIV), human adenovirus, herpes simplex virus (HSV), Streptococcus pyogenes, and Toxoplasma gondii.^[3]

• Relative bradycardia, Faget’s sign, is when the “pulse is less than expected at a given body temperature”^[4] Relative bradycardia suggests an intracellular organism such as salmonella, legionella, and chlamydia.^[4] Other causes include Sandfly fever, Dengue fever, and maybe some cases of drug induced fever^[5].

• Arthropathy, when prominent, suggests Parvovirus B19.

• Myalgias, when prominent, suggests Dengue fever. When myalgias localize to the calves, low back, or abdomen, consider leptospirosis.

• Headache, when prominent, suggests West Nile Virus.

• Conjunctival injection, when prominent, suggests Dengue fever, Chikungunya fever, or leptospirosis.

• Liver and renal failure when present, suggest leptospirosis (“Weil’s disease”)

• Vertebral osteomyelitis or spondylitis suggests brucellosis