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close this bookWHO Recommended Surveillance Standards (WHO; 1999; 157 pages)
View the documentAcknowledgements
View the documentAcronyms
View the documentIntroduction
View the documentNational Coordination of Communicable Disease Surveillance
View the documentExplanatory notes
View the documentSurveillance activities: criteria and WHO Department
View the documentCommunicable disease contacts in Regional Offices
close this folderDiseases
View the documentB20-B21-B22-B23-B24 AIDS
View the documentA22 Anthrax
View the documentA23 Brucellosis
View the documentA00 Cholera
View the documentA81.0 Creutzfeldt-Jakob disease
View the documentA90, A91 Dengue fever (A90) including Dengue haemorrhagic fever (DHF) & Dengue shock syndrome (DSS, A91)
View the documentA36 Diphtheria
View the documentB72 Dracunculiasis (Guinea worm disease)
View the documentA98.3, A98.4 Ebola-Marburg viral diseases
View the documentA83.0 Japanese encephalitis
View the documentB74 Lymphatic filariasis
View the documentB96.3 Haemophilus influenzae type b
View the documentB15-B17 Acute viral hepatitis
View the documentB20-B24 HIV infection
View the documentJ10, J11 Influenza
View the documentA96.2 Lassa fever
View the documentA48.1 Legionellosis
View the documentB55.1, B55.2 Cutaneous leishmaniasis
View the documentLeishmania / HIV co-infections
View the documentB55.0 Visceral leishmaniasis
View the documentA30 Leprosy
View the documentA27 Leptospirosis
View the documentB50-54 Malaria
View the documentB05 Measles
View the documentA39 Meningococcal disease
View the documentA87 Viral meningitis
View the documentB73 Onchocerciasis
View the documentA37.0 Pertussis
View the documentA20 Plague
View the documentA36 Poliomyelitis
View the documentA82 Rabies
View the documentA02.0 Salmonellosis
View the documentB65 Schistosomiasis
View the documentA50-52 Syphilis
View the documentA33 Tetanus, neonatal
View the documentB56-0, B56-1 African trypanosomiasis
View the documentB57 American trypanosomiasis
View the documentA15-A19 Tuberculosis
View the documentA75.3 Scrub typhus
View the documentA95.9 Yellow fever
open this folder and view contentsSyndromes
View the documentAnnex 1 Software free and in the public domain
View the documentAnnex 2 Proposed surveillance definitions
View the documentAnnex 3 Role and use of Geographic Information Systems (GIS) and mapping for epidemiological surveillance

A96.2 Lassa fever


This severe acute viral infection has the potential to produce epidemics, and as such surveillance mechanisms to detect outbreaks and to monitor control measures are critical in affected countries.


Clinical description

An illness of gradual onset with one or more of the following:


malaise, fever, headache, sore throat, cough, nausea, vomiting, diarrhoea, myalgia, chest pain, hearing loss, and

A history of contact with excreta of rodents or with a probable or confirmed case of Lassa fever.

Laboratory criteria for diagnosis


• Isolation of virus (only in laboratory of biosafety level 4) from blood, urine or throat washings or
• Positive IgM serology or seroconversion (IgG antibody) in paired serum specimens or
• Demonstration of Lassa virus antigen in autopsy tissues by immunohistochemistry or in serum by ELISA
• Positive PCR from serum or autopsy tissues

Case classification

Suspected: A case compatible with the clinical description.

Probable: A suspected case that is epidemiologically linked to a confirmed case.

Confirmed: A suspected case that is laboratory-confirmed.

Contact: A person having close personal contact with the patient (living with, caring for) or a person testing the laboratory specimens of a patient in the 3 weeks after the onset of the illness.


Endemic situation:

Immediate reporting of case-based data of suspected, probable or confirmed cases from peripheral level to intermediate and central levels.

All cases must be investigated, and contact tracing undertaken.

Routine monthly reporting of aggregated data from intermediate to central level.

Outbreak situation:

All suspected outbreaks must be reported centrally. Surveillance must be intensified with active case finding and contact tracing. Aggregated data on a daily/weekly basis to be submitted to intermediate and central level by investigation team.

The disease is endemic in Sierra Leone, Liberia, Guinea and regions of Nigeria. Outside these areas, compatible symptoms, with a history of travel to or arrival from one of these countries, should prompt investigation and reporting.


Case-based data for reporting and investigation


• Case classification (suspected/probable/confirmed)
• Unique identifier, age, sex, place of residence for the three weeks before onset of illness
• Date of onset
• Hospitalization
• Outcome

Aggregated data for reporting

Endemic situation


• Number of cases (suspect/probable/confirmed) by geographical area and by outcome
• Contacts by geographical area, success of tracing and outcome

Outbreak situation


• Total number of cases by village, geographical area, onset date, hospitalization, outcome
• New cases and contacts identified since last report
• Total number of contacts by outcome
• New contacts identified and traced since last report



• Mapping number of cases by geographical area
• Percentage of contacts followed up
• Case-fatality rate



• Monitoring endemic disease over time
• Identification of risk groups or areas
• Identification of clusters/outbreaks
• Investigation of cases, contacts and source of infection


Extreme biohazard is associated with sample collection and transport and with laboratory investigations.


Regional Offices

See Regional Communicable Disease contacts on section "Communicable disease contacts in Regional Offices".

Headquarters: 20 Avenue Appia, CH-1211 Geneva 27, Switzerland

Department of Communicable Diseases Surveillance and Response (CSR)


E-mail: arthurr@who.ch / outbreak@who.ch
Tel: (41 22) 791 2658/2636/2111
Fax: (41 22) 791 48 78
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