A 45-year-old man with history of IV drug use presents to the outpatient clinic with a history of fever for 5 days. He also endorses sweats, headache behind the eyes, sore throat, muscle and joint pain, and a new rash seen in Figure A. He reports that he traveled to Africa last year and returned from a vacation to Thailand 10 days ago. His immunizations are up to date, although he missed the pre-departure travel medicine consult before his trip to Thailand. His temperature is 101.5°F (38.6°C), blood pressure is 125/80 mmHg, pulse is 105/min, and respirations are 14/min. Laboratory testing reveals the following:

Leukocyte count: 2,400/mm^3
Hemoglobin: 13.4 g/dL
Hematocrit: 40%
Mean corpuscular volume: 81 µm^3
Platelets: 92,000/mm^3

Serum:
AST: 112 IU/L
ALT: 69 IU/L
ALP: 78 IU/L
Bilirubin: 0.9 mg/dL

Which of the following is the diagnostic test of choice for this disease?
Blood smear
Sputum with acid fast stain
Serologic testing
Stool culture
Serologic testing
This patient is presenting with fever, headache with retro-orbital pain, muscle aches, joint pain, rash, leukopenia and thrombocytopenia, which are classic findings for dengue fever. The diagnostic test of choice for dengue is serology.

Dengue is a viral infection endemic to South Asia, Central and South America, and the Caribbean. Although most infections are asymptomatic, notable characteristics include headache with retro-orbital pain, bone pain ("break-bone fever"), leukopenia, and thrombocytopenia (< 100,000 /µL). Symptoms typically develop several days to 2 weeks following the bite of an infected mosquito. The diagnostic test of choice is a serologic antibody test, although PCR can also be used in the acute (< 3 days) phase of illness. Treatment is with supportive care including rehydration.

Jasamai et al. present the current treatment options for dengue fever. They discuss how supportive therapy is the mainstay of treatment as no antibody or antiviral treatments have been effective at this time. They recommend using effective preventive measures such as mosquito control in endemic areas.

Figure A is a clinical photograph demonstrating the maculopapular rash seen in dengue fever.

Incorrect Answers:
Answer A: Blood culture is used for the detection of bacterial infections of the blood. This patient's IV drug use puts him at risk for bacterial endocarditis, but he does not have other expected findings, such as new murmur, Janeway lesions, Roth spots, or Osler nodes. Endocarditis should be treated with intravenous antibiotics.

Answer B: Blood smear is the diagnostic test of choice for other mosquito-borne diseases such as malaria. It is not used in the detection of dengue. Malaria presents with cyclical fevers and organisms on blood smear. It can be treated with chloroquine and artesunate.

Answer D: Sputum with acid fast stain is the test of choice for tuberculosis. This patient has a risk factor of TB as he recently traveled to Africa, but he does not have any pulmonary symptoms. Treatment for tuberculosis is rifampin, isoniazid, pyrazinamide, and ethambutol therapy (among other possible regimens).

Answer E: Stool culture may be used to diagnose typhoid fever. Typhoid fever presents with many of the same non-specific symptoms as dengue but would also present with prominent abdominal pain and gastrointestinal symptoms. Typhoid can be treated with antibiotics such as ciprofloxacin.

Bullet Summary:
Dengue fever is characterized by fever, headache with retro-orbital pain, muscle and joint pain, rash, leukopenia and thrombocytopenia that can be diagnosed through serologic testing.