A95.9 Yellow fever

Case report universally required by International Health Regulations

RATIONALE FOR SURVEILLANCE

This mosquito-borne virus disease occurs in tropical regions of Africa and South America and is maintained by sylvatic transmission of virus involving forest-dwelling mosquitoes and monkeys. Transmission to humans may occur in forest transition zones and may subsequently enter an urban cycle through Aedes aegypti. Many cities are now threatened with epidemics as yellow fever is undergoing a major resurgence especially in the African region. Surveillance data allow for monitoring disease incidence, prediction and early detection of outbreaks and monitoring of control measures.

Strategies for yellow fever control include control of Ae. aegypti in urban centres, infant immunization, vaccination campaigns, outbreak prevention, epidemic detection and control.

Case reporting is universally required by International Health Regulations.

RECOMMENDED CASE DEFINITION

Clinical description

Characterized by acute onset of fever followed by jaundice within 2 weeks of onset of first symptoms. Haemorrhagic manifestations and signs of renal failure may occur.

Laboratory criteria for diagnosis

Isolation of yellow fever virus, or

Presence of yellow fever specific IgM or a four-fold or greater rise in serum IgG levels in paired sera (acute and convalescent) or

Positive post-mortem liver histopathology or

Detection of yellow fever antigen in tissues by immunohistochemistry or

Detection of yellow fever virus genomic sequences in blood or organs by PCR

Case classification

Suspected: A case that is compatible with the clinical description.

Probable: Not applicable.

Confirmed: A suspected case that is laboratory-confirmed (national reference lab) or epidemiologically linked to a confirmed case or outbreak.

RECOMMENDED TYPES OF SURVEILLANCE:

Routine weekly/monthly reporting of aggregated data on suspected and confirmed cases from peripheral to intermediate and central level. Zero reporting required at all levels.

Immediate reporting of suspected cases from peripheral to intermediate and central levels.

All suspected cases and outbreaks must be investigated immediately and laboratory-confirmed.

Case-based surveillance must be implemented in countries identified by WHO as being at high risk for yellow fever. Specimens must be collected to confirm an epidemic as rapidly as possible. Priority is placed on collecting specimens from new or neighbouring areas (other than the area where the epidemic is already confirmed).

International: Mandatory reporting of all suspected and confirmed cases within 24 hours to WHO.

RECOMMENDED MINIMUM DATA ELEMENTS

Aggregated data for reporting

Number of cases

Doses of yellow fever vaccine administered to infants, by geographical area

Completeness/timeliness of monthly reports

Case-based data for reporting and investigation

Unique identifier

Geographical area name (district and province)

Date of birth

Date of onset

Date of notification

Date of investigation

Ever received a dose of yellow fever vaccine? (1 = yes; 2 = no; 9 = unknown)

Date acute blood specimen received in laboratory

Date convalescent blood specimen received in laboratory (if applicable)

Date histopathology specimen collected (if applicable)

Depending on which laboratory tests used:

· IgM (1 = positive; 2 = negative; 3 = no specimen processed; 9 = unknown)
· virus isolation (1 = positive; 2 = negative; 3 = no specimen processed; 9 = unknown)
· IgG (4-fold rise) (1 = positive; 2 = negative; 3 = no specimen processed; 9 = unknown)
· liver

Date IgM results first sent

Date virus isolation results first sent

Final classification

Date histopathology report first sent

Date convalescent blood specimen received in laboratory (if applicable)

Date histopathology specimen collected

Date IgG results first sent

Final classification (1 = confirmed; 2 = suspected; 4 = discarded)

Final outcome (1 = alive; 2 = dead; 9 = unknown)

RECOMMENDED DATA ANALYSES, PRESENTATION, REPORTS

Aggregated data

· Incidence rate by month, year, and geographic area
· Yellow fever vaccine coverage by year and geographic area
· Completeness/timeliness of monthly reporting

Case-based data same as aggregated data plus the following:

· Confirmed cases by age group, immunization status, geographic area, month, year
· Case-fatality rate
· Final classification of all suspected cases

PERFORMANCE INDICATORS OF SURVEILLANCE QUALITY TARGET

	target
Completeness of monthly reporting	³90%
Percent of all suspect cases for which specimens were collected	³50%*
If IgM test is done: Laboratory results sent £3 days of receipt of acute blood specimen	³80%
If virus isolation is done: results sent £ 21 days of receipt of acute blood specimen	³80%
If IgG test is done: results sent £3 days of receipt of convalescent blood specimen	³80%

* Target during non-outbreak periods. Once an outbreak is confirmed, the priority is to detect outbreaks in neighbouring areas and confirm them in the laboratory.

PRINCIPAL USES OF DATA FOR DECISION-MAKING

· Investigate suspect cases and collect laboratory specimens to confirm an outbreak and mobilize emergency immunization activities

· Monitor yellow fever vaccine coverage by geographic region to monitor progress and identify areas of poor performance so that corrective actions can be taken

· Monitor disease incidence to assess impact of control efforts

SPECIAL ASPECTS

At risk for yellow fever epidemics in Africa: Angola, Benin, Burkina Faso, Burundi, Cameroon, Cape Verde, Central African Republic, Chad, Congo, Côte d'Ivoire, Democratic Republic of Congo (formerly Zaire), Equatorial Guinea, Eritrea, Ethiopia, Gabon, Gambia, Ghana, Guinea, Guinea-Bissau, Liberia, Kenya, Mali, Mauritania, Niger, Nigeria, Rwanda, Senegal, Sierra Leone, Somalia, Sudan, Tanzania, Togo, Uganda.

In America: Bolivia, Brazil, Colombia, Ecuador, Guyana, French Guiana, Panama, Peru, Surinam, Venezuela.

CONTACT

Regional Offices

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

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

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