-from Epidemiological Bulletin, Vol. 21 No. 2, June 2000-

Case Definitions:
Dengue and Leptospirosis

• Dengue
• Leptospirosis

Dengue

Rationale for surveillance
Dengue fever, including Dengue Hemorrhagic Fever (DHF) and Dengue Shock Syndrome (DSS), is the most significant arthropod-borne viral disease worldwide. It occurs in over 100 countries and territories and threatens the health of over 2,500 million people in tropical and subtropical regions. Dengue fever is a severe disease with high epidemic potential. An estimated 500,000 patients, 90% of them below the age of 15, are hospitalized with DHF/DSS every year. The World Health Organization (WHO) aims to accelerate the final development of an attenuated dengue vaccine.

Recommended case definition
Dengue fever:
Clinical description: An acute febrile illness of 2-7 days duration with 2 or more of the following: headache, retro-orbital pain, myalgia, arthralgia, rash, hemorrhagic manifestations, leucopenia.

Laboratory criteria for diagnosis:
One or more of the following:

• Isolation of the dengue virus from serum, plasma, leukocytes, or autopsy samples,
• Demonstration of a fourfold or greater change in reciprocal IgG or IgM antibody titers to one or more dengue virus antigens in paired serum samples,
• Demonstration of dengue virus antigen in autopsy tissue by immunohistochemistry or immunofluorescence or in serum samples by EIA,
• Detection of viral genomic sequences in autopsy tissue, serum or CSF samples by polymerase chain reaction (PCR).

Case classification
Suspected: A case compatible with the clinical description.

Probable: A case compatible with the clinical description with one or more of the following:

• supportive serology (reciprocal hemagglutination-inhibition antibody titre greater than 1280, comparable IgG EIA titre or positive IgM antibody test in late acute or convalescent-phase serum specimen),
• ccurrence at same location and time as other confirmed cases of dengue fever.

Confirmed: A case compatible with the clinical description, laboratory-confirmed.

Criteria for Dengue Hemorrhagic Fever/Dengue Shock Syndrome:
Dengue Hemorrhagic Fever: A probable or confirmed case of Dengue and Hemorrhagic tendencies evidenced by one or more of the following:

• Positive tourniquet test
• Petechiae, ecchymoses or purpura
• Bleeding: mucosa, gastrointestinal tract, injection sites or other
• Haematemesis or melaena
  and thrombocytopenia (100 000 cells or less per mm3)
  and evidence of plasma leakage due to increased vascular permeability, manifested by one or more of the following:
• more than 20% rise in average hematocrit for age and sex
• more than 20% drop in hematocrit following volume replacement treatment compared to baseline
• signs of plasma leakage (pleural effusion, ascites, hypoproteinemia)

Dengue shock syndrome: All the above criteria, plus evidence of circulatory failure manifested by rapid and weak pulse, and narrow pulse pressure (less than 20 mm Hg) or hypotension for age, cold, clammy skin and altered mental status.

Recommended types of surveillance
Areas where no dengue transmission has been detected but where Aedes aegypti occurs: surveillance of suspected cases with investigation of clusters of suspected cases for dengue.

Countries where disease is endemic with seasonal variations in transmission, and areas where epidemic dengue occurs: routine weekly/monthly reporting of aggregated data of suspected, probable and confirmed cases from peripheral to intermediate and central levels.

Recommended minimum data elements
Case-based data at the peripheral level

• Case classification (suspected/probable/confirmed), serotype, DHF/DSS present (Yes/No)
• Unique identifier, name of patient, age, sex, geographical information
• Date of onset
• Hospitalized (Yes/No)
• Outcome
• Travel history during past 2 weeks

Aggregated data for reporting

• Number of cases by age group
• Number of confirmed (and serotype)
• Number of DHF/DSS cases by age group
• Number of hospitalizations and deaths

Principal use of data for decision-making

• Target high risk areas for intervention.
• Monitor changes in serotype and rate of DHF/DSS.
• Monitor trends in endemic disease or re-emergence of disease.

Back to top

For additional information and previous articles on dengue in the Americas, click here.

Leptospirosis

Rationale for surveillance
This zoonosis with worldwide distribution occurs seasonally in countries with a humid subtropical or tropical climate. It is often linked to occupation, sometimes in outbreaks. Feral and domestic animal species may serve as sources of infection with one of the Leptospira serovars. Infection is transmitted to humans through direct contact with (the urine of) infected animals or a urine-contaminated environment, mainly surface waters, soil and plants. The course of disease in humans ranges from mild to lethal. Leptospirosis is probably underreported in many countries because of difficult clinical diagnosis and lack of diagnostic laboratory services. Surveillance provides the basis for intervention strategies in human or veterinary public health.

Recommended case definition
Clinical description
Acute febrile illness with headache, myalgia and prostration associated with any of the following symptoms:

• conjunctival suffusion
• meningeal irritation
• anuria or oliguria and/or proteinuria
• jaundice
• hemorrhages (from the intestines; lung bleeding is notorious in some areas)
• cardiac arrhythmia or failure
• skin rash
  and a history of exposure to infected animals or an environment contaminated with animal urine.
  
  Other common symptoms include nausea, vomiting, abdominal pain, diarrhoea, arthralgia.

Laboratory criteria for diagnosis

• Isolation (and typing) from blood or other clinical materials through culture of pathogenic leptospires
• Positive serology, preferably Microscopic Agglutination Test (MAT), using a range of Leptospira strains for antigens that should be representative of local strains.

Case classification
Suspected: A case that is compatible with the clinical description.
Probable: Not applicable.
Confirmed: A suspected case that is confirmed in a competent laboratory.

Note: Leptospirosis is difficult to diagnose clinically in areas where diseases with symptoms similar to those of leptospirosis occur frequently.

Recommended types of surveillance
a) Immediate case-based reporting of suspected or confirmed cases from peripheral level (hospital/general practitioner/laboratory) to intermediate level (and from intermediate level to central level for no endemic areas). All cases must be investigated.

b) In endemic areas, routine reporting of aggregated data of confirmed cases from intermediate to central level.

c) International: The International Leptospirosis Society and the WHO Collaborating Centers on Leptospirosis collect data worldwide and regionally on leptospirosis.

Note:

• Hospital-based surveillance may give information on severe cases of leptospirosis.
• Serosurveillance using sera available in public health laboratories, collected for other purpose, or sera collected in programmed survey may give information on whether leptospiral infections occur or not in certain areas or populations.

Recommended minimum data elements

• Age, sex, address, occupation
• Clinical symptoms (morbidity, mortality)
• Hospitalization (Yes/No)
• History and place of exposure (animal contact, environment, occupational)
• Microbiological and serological data
• Date of diagnosis
• Meteorological data, e.g. rainfall, flooding, natural disaster

Aggregated data for reporting

• Number of cases
• Number of hospitalizations
• Number of deaths
• Number of cases by type (causative serovar / serogroup) of leptospirosis.

Principal use of data for decision-making

• Assess the magnitude of the problem in different areas and risk factors (groups/areas/conditions).
• Identify outbreaks.
• Identify animal sources of infection.
• Monitor for emergence of leptospirosis in new areas and new risk (occupational) groups.
• Design rational control or prevention methods.
• Identify new serovars and their distribution.
• Inform on locally occurring serovars for a representative range in the MAT (Monoclonal Antibody Test).

Back to top

Return to the Index,
Epidemiological Bulletin , Vol. 21 No. 2, June 2000