Diagnosis

The diagnosis of dengue is typically made clinically, on the basis of reported symptoms and physical examination; this applies especially in endemic areas.[1] However, early disease can be difficult to differentiate from other viral infections.[5] A probable diagnosis is based on the findings of fever plus two of the following: nausea and vomiting, rash, generalized pains, low white blood cell count, positive tourniquet test, or any warning sign (see table) in someone who lives in an endemic area.[23] Warning signs typically occur before the onset of severe dengue.[8] The tourniquet test, which is particularly useful in settings where no laboratory investigations are readily available, involves the application of a blood pressure cuff for five minutes, followed by the counting of any petechial hemorrhages; a higher number makes a diagnosis of dengue more likely.[8] It can be difficult to distinguish dengue fever and chikungunya, a similar viral infection that shares many symptoms and occurs in similar parts of the world to dengue.[7] Often, investigations are performed to exclude other conditions that cause similar symptoms, such as malaria, leptospirosis, typhoid fever, and meningococcal disease.[5]

The earliest change detectable on laboratory investigations is a low white blood cell count, which may then be followed by low platelets and metabolic acidosis.[5] In severe disease, plasma leakage results in hemoconcentration (as indicated by a rising hematocrit) and hypoalbuminemia.[5] Pleural effusions or ascites can be detected by physical examination when large,[5] but the demonstration of fluid on ultrasound may assist in the early identification of dengue shock syndrome.[1][5] The use of ultrasound is limited by lack of availability in many settings