Severe dengue
2026 Case Definition

Clinical Criteria

In the absence of a more likely alternative diagnosis:

• Clinical evidence of dengue includes fever or chills as reported by the patient or healthcare provider^¶ AND the presence of one or more of the following manifestations:
  • Nausea or vomiting, which may be persistent (e.g., ≥3 episodes in 1 hour or ≥4 episodes in 6 hours)
  • Rash
  • Headache
  • Retro-orbital pain
  • Arthralgia (joint pain)
  • Myalgia (muscle aches)
  • Positive tourniquet test
  • Leukopenia (e.g., a total white blood cell count of <5,000/mm3)
  • Thrombocytopenia (e.g., platelet count <150,000/mm3)
  • Abdominal pain or tenderness
  •  Extravascular fluid accumulation (e.g., pleural or pericardial effusion, ascites) without respiratory distress
  • Mucosal bleeding^# (e.g., gums, nose [epistaxis], vagina [menorrhagia], kidney [macroscopic hematuria] or mild GI bleeding)
  • Liver enlargement >2 centimeters
  • Increasing hematocrit (>20% in 2 measurements taken 6 hours apart).

^¶ The vast majority of dengue cases are characterized by fever or chills. If fever or chills are not present, careful consideration of patient’s clinical course, exposure history, and environmental risk are recommended.

^# If bleeding is severe, consider severe dengue (see below).

Suspect

• Meets clinical criteria for dengue AND meets epidemiological linkage criteria AND with no laboratory testing performed, OR
• Meets clinical criteria for dengue AND meets epidemiological linkage criteria AND has negative IgM results with no PCR/NS1 testing on a sample collected <5 days after illness onset.

Probable

• Meets clinical criteria for dengue AND meets presumptive laboratory evidence AND meets epidemiologic linkage criteria.

Confirmed

• Meets clinical criteria for dengue AND meets confirmatory laboratory evidence, OR
• Meets non-antibody based confirmatory laboratory evidence AND meets epidemiologic linkage criteria AND
  • Has clinical evidence of fever or chills only, OR
  • Has other clinical evidence compatible with dengue in the absence of fever or chills.

Background

Dengue is a potentially fatal acute febrile illness caused by infection with any of four dengue viruses (DENV-1, -2, -3 and -4). Dengue is a major public health problem worldwide, with an estimated 400 million DENV infections and 100 million clinically apparent dengue cases occurring annually. Approximately 75% of individuals infected with DENV are asymptomatic. Among those who develop symptoms, approximately 5% will progress to severe dengue, an illness characterized by plasma leakage, hypovolemic shock, hemorrhage, and potentially death. DENV is primarily transmitted through the bite of infected Aedes species mosquito vectors (Ae. aegypti and Ae. albopictus); less common transmission routes include blood transfusion, organ transplantation, laboratory exposure, and perinatal infection.

Laboratory Criteria

Confirmatory Laboratory Evidence: 

• Detection of dengue virus (e.g., growth in cell culture), viral antigen (e.g., non-structural protein [NS1] antigen-capture enzyme-linked immunosorbent assay [ELISA], immunohistochemistry), or viral ribonucleic acid (RNA) (e.g., PCR)) in a serum, plasma, blood, cerebral spinal fluid (CSF), other body fluid, or tissue specimen, OR
• Detection of anti-DENV immunoglobulin (IgM) antibodies in a serum or CSF specimen AND
  • Detectable DENV-specific neutralizing antibody titers by plaque reduction neutralization (PRNT)^*, AND
  • Negative neutralizing antibody titers against other flaviviruses endemic to the region where exposure occurred.

Presumptive Laboratory Evidence: 

• Detection of anti-DENV IgM antibodies in a serum specimen,^† OR
• Demonstration of a ≥4-fold rise in DENV-specific neutralizing antibody titers in paired serum samples optimally collected ≥2 weeks apart with a ≥4-fold higher end point titer as compared to other flaviviruses tested.^‡

Note: The categorical labels used here to stratify laboratory evidence are intended to support the standardization of case classifications for public health surveillance. The categorical labels should not be used to interpret the utility or validity of any laboratory test methodology.

^* Dengue virus immunoglobulin (IgG) and neutralizing antibodies can persist for many years following a symptomatic or asymptomatic infection. A high proportion of people living in dengue-endemic areas have experienced a previous dengue infection; the presence of neutralizing antibodies alone is only evidence of previous infection. In a single sample, plaque reduction neutralization tests (PRNTs) can help rule out other flaviviruses but cannot differentiate between recent and remote (unrelated to the current illness) infection from DENV among people with previous exposure.

^† In the setting of an outbreak or known transmission of another flavivirus (e.g., Zika or West Nile virus), obtaining negative IgM results for the other flaviviruses is recommended. If IgM antibodies from other flaviviruses are detected and neutralizing antibodies are unable to differentiate flaviviruses, consider reporting the case as ‘Flavivirus disease, not otherwise specified.

^‡ During a second flavivirus infection, cross-reactive antibodies from the first infecting dengue virus serotype or flavivirus (the “original antigen”) can predominate over the current infecting flavivirus. Neutralizing antibody results should be interpreted with caution when previous dengue infection is suspected or when titers are high against multiple dengue virus serotypes or flaviviruses.

Epidemiologic Linkage

• Resided in or traveled to an area with a risk^§ of DENV transmission in the 14 days before the onset of symptoms, OR
• Association in time and place before onset of symptoms (e.g., household member, family member, classmate, coworker, or neighbor) with a confirmed or probable dengue case, OR
• Laboratory exposure to DENV within 14 days of onset of symptoms, OR
• Receipt of blood, blood products, organ transplant, or other tissue transplant within 30 days of symptom onset from a person who has either been diagnosed with DENV infection or returned from traveling to an area with risk^§ of DENV transmission in the 14 days before donation.

^§ Visit Areas with Risk of Dengue | Dengue | CDC for geographic areas with known current or previous risk of DENV; for areas where cases have not been previously identified, consult with CDC for assistance on risk determination.

Criteria to Distinguish a New Case from an Existing Case

DENV infection results in long-lasting immunity to symptomatic dengue infection with that DENV-type. However, cross-protective (heterotypic) immunity against DENV infection is short-lived, with estimated durations of 1–3 years. In DENV endemic areas where infection pressure is high, individuals have been shown to infrequently have sequential episodes of dengue with two different infecting serotypes. Additionally, detectable IgM anti-DENV can persist for approximately 90 days.

• A person with two clinical episodes of dengue occurring at least two weeks apart and shown to be due to different infecting serotypes confirmed by molecular diagnostic testing would have the subsequent episode enumerated as a new case, resulting in two cases being counted, OR
• In the absence of molecular testing evidence showing infection due to different infecting serotypes, a person with two clinical episodes of dengue occurring more than 90 days apart would have the subsequent episode enumerated as a new case, resulting in two cases being counted.