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Am Fam Physician. 2021;103(2):113-114

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A 33-year-old patient presented with a rash that developed two days earlier and was preceded by fever, headache, nausea, and arthralgias. The rash was worse on the limbs. The medical history was unremarkable, but the patient had recently traveled to the Philippines.

Physical examination revealed a diffuse, erythematous, maculopapular rash on the arms and legs (Figure 1). Findings on a tourniquet test were positive (Figure 2). Laboratory testing was positive for leukopenia and thrombocytopenia. A chest radiograph showed right-sided pleural effusion.


Based on the patient's history and physical examination findings, which one of the following is the most likely diagnosis?

  • A. Acute HIV infection

  • B. Chikungunya virus infection.

  • C. Dengue.

  • D. Malaria.

  • E. Zika virus infection.


The answer is C: dengue, a common mosquito-borne disease encountered in more than 100 tropical and subtropical countries in North and South America, Africa, the Middle East, Asia, and the Pacific Islands. The incidence is increasing, and outbreaks are becoming more common, including in the Caribbean and the Big Island of Hawaii.1 The disease is caused by one of four dengue viruses transmitted by Aedes aegypti and Aedes albopictus mosquitos. Most cases in the United States are travel-related, except in Puerto Rico where dengue is endemic.2

Humans are the primary reservoirs for dengue. Patients with the disease may be asymptomatic or have mild to severe or life-threatening symptoms. Common presenting symptoms include high-grade fever, headache, retroorbital pain, myalgias/arthralgias, nausea, vomiting, and rash. The disease progresses to severe dengue in one out of 20 patients.1 Severe dengue follows three phases: febrile, critical, recovery. The critical phase occurs after 72 hours of fever and is distinguished by increased vascular permeability, fever, hemorrhagic manifestations, and marked thrombocytopenia.

Diagnosis of dengue is based on clinical signs and symptoms. The tourniquet test is commonly used.3 To perform this test, a blood pressure cuff is inflated on the arm, then removed. After two minutes, petechiae are counted below the antecubital fossa. The test is positive if there are 10 or more petechiae per 1 square inch (Figure 2). The Centers for Disease Control and Prevention recommends testing symptomatic patients with a history of travel to endemic areas.4

Acute HIV infection, also known as primary HIV infection or acute retroviral syndrome, is the period just after initial HIV infection, generally before seroconversion.5 Symptoms are characterized as mononucleosis-like or flulike, with the most prevalent symptoms being fever, fatigue, myalgias/arthralgias, rash, pharyngitis, lymphadenopathy, and mucocutaneous ulcerations.5

Chikungunya virus infection and dengue have similar symptoms and are transmitted by the same mosquito vectors.6 Chikungunya virus infection is characterized by fever and intense joint pain but lacks leukopenia and thrombocytopenia. Headache, myalgias, and rash are also possible.7 The laboratory diagnosis of Chikungunya virus infection is based on viral isolation.6

Malaria is a parasitic infection. In the United States, malaria mainly occurs in travelers who have returned from endemic regions.8 Fever and splenomegaly are the most common physical examination findings.8

Zika virus infection also presents similarly to dengue and is transmitted by the same mosquito vectors.9 Unlike dengue, Zika virus infection is commonly associated with conjunctivitis.9 The disease is diagnosed through serology or reverse transcriptase–polymerase chain reaction testing.10

ConditionCharacteristicsSigns and symptoms
Acute HIV infectionPeriod just after initial HIV infection, generally before seroconversion; also called primary HIV infection or acute retroviral syndromeMononucleosis-like or flulike; fever, fatigue, myalgias/arthralgias, rash, pharyngitis, lymphadenopathy, and mucocutaneous ulcerations
Chikungunya virus infectionSimilar to dengue but lacks leukopenia and thrombocytopenia; transmitted by same mosquito vectors as dengueFever and intense joint pain; headache, myalgias, and rash are also possible
DengueCan be diagnosed using the tourniquet test; severe illness has three phases: febrile, critical, and recovery; transmitted by Aedes aegypti and Aedes albopictus mosquitosHigh-grade fever, headache, retroorbital pain, myalgias/arthralgias, nausea, vomiting, and rash
MalariaParasitic infectionFever and splenomegaly
Zika virus infectionTransmitted by same mosquito vectors as dengue; can cause birth defects, such as microcephaly, if the mother is infected during pregnancyOften asymptomatic; if present, symptoms are similar to dengue, but conjunctivitis is more common

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This series is coordinated by John E. Delzell Jr., MD, MSPH, associate medical editor.

A collection of Photo Quiz published in AFP is available at

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