A27

Leptospirosis
RATIONALE FOR SURVEILLANCE

Leptospirosis is a zoonosis with a world-wide distribution. It occurs most frequently in countries with a humid subtropical or tropical climate, often seasonally, often linked to certain occupations, sometimes in outbreaks. A wide variety of feral and domestic animal species may serve as sources of infection with one of the many Leptospira serovars. The infection is transmitted to humans by direct contact with (the urine of) infected animals or a urine-contaminated environment, mainly surface waters, soil and plants. The course of the disease in humans ranges from mild to lethal. Leptospirosis is probably overlooked and underreported in many countries due to the difficult clinical diagnosis and the lack of diagnostic laboratory services. Surveillance provides the basis for intervention strategies in human or veterinary public health.
RECOMMENDED CASE DEFINITION

Clinical description

An acute febrile illness with headache, myalgia and prostration associated with any of the following symptoms:

  • conjunctival suffusion
  • meningeal irritation
  • an-/oliguria and/or proteinuria
  • jaundice
  • haemorrhages (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: nausea, vomiting, abdominal pain, diarrhoea, arthralgia

Laboratory criteria for diagnosis

  • Isolation (and typing). from blood or other clinical materials by culture of pathogenic leptospires
  • Positive serology preferably by the Microscopic Agglutination Test (MAT) using a panel of Leptospira strains for antigens that, ideally, is representative of the locally occurring strains

Case classification

Suspected: A case that is compatible with the clinical description
Probable: Not applicable
Confirmed: A suspect 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

Immediate case-based reporting of suspected or confirmed cases from peripheral level (hospital /general practitioner/laboratory) to intermediate level. All cases should be investigated.
Routine reporting of aggregated data of confirmed cases from intermediate to central level.
International: The International Leptospirosis Society collects world-wide data on occurrence of leptospirosis

Comment:
Hospital based surveillance may give information on mainly severe cases of leptospirosis.

Serosurveillance may give information on whether leptospiral infections occur or not in certain areas or populations.

RECOMMENDED MINIMUM DATA ELEMENTS.

Individual patient record for reporting and investigation

  • Age, sex, geographical information, occupation
  • Clinical symptoms (morbidity, mortality)
  • Hospitalisation (Y/N)
  • History and place of exposure (animal contact, environment)
  • Microbiological and serological data
  • Date of diagnosis
  • Rainfall, flooding

Aggregated data for reporting

  • Number of cases
  • Number of hospitalisations
  • Number of deaths
  • Number of cases by type (causative serovar/serogroup) of leptospirosis
RECOMMENDED DATA ANALYSES, PRESENTATION, REPORTS

Number of cases by age, sex, occupation, area, date of onset, causative serovars/serogroups, (presumptive) infection source, transmission conditions (graphs, tables, maps).
Frequency distribution of signs and symptoms by case and causative serovar (tables).
Reports of outbreaks, reports of preventive measures, surveillance of the human population and populations of feral and domestic animals.
PRINCIPAL USES OF DATA FOR DECISION MAKING:
  • Assess the magnitude of the problem in different areas and risk 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 panel in the MAT
SPECIAL ASPECTS

Serology by MAT may provide presumptive information on causative serogroups.

Attempts should be made at isolation of leptospires and isolates should be typed to assess locally circulating serovars.
Questioning the patient may provide clues to infection source and transmission conditions.
Animal serology may give presumptive information on serogroup status of the infection;
Isolation followed by typing gives definite information on serovar.

CONTACT

Headquarters

WHO Division of Emerging and other Communicable Diseases Surveillance and Control (EMC)
20 Avenue Appia, CH-1211 Geneva 27, Switzerland
E-mail: cosivio@who.ch / outbreakemc@who.ch
Tel: (41 22) 791 2531 / 4687 / 2111
Fax: (41 22) 791 4893 / 0746 attn EMC