Yellow Fever
Case
Definition
RATIONALE FOR SURVEILLANCE
Jungle yellow fever continues to be an
important cause of morbidity and mortality in the Americas. Urban
yellow fever has been eliminated from the Americas several
decades ago. However there is a risk of its re-emergence due to
the widespread infestation of the Aedes aegypti mosquito
in the American continent, migration patterns, and low
vaccination rates with the yellow fever vaccine. The seriousness
of the current yellow fever situation in the Region requires a
firm commitment by countries to a strong and effective strategy
for controlling this disease. Countries should implement routine
yellow fever immunization in children one year of age in
conjunction with measles vaccination. High immunization coverage
is also recommended for all other age groups living or entering
yellow fever enzootic areas, as well as contagious areas infested
with Aedes aegyipti. Heightened surveillance is essential
for effective and timely case identification, outbreak response,
and improvements in vaccination strategies, including advance
preparation for implementing emergency immunization activities .
RECOMMENDED CASE DEFINITIONS
- Clinical case definition:
An illness characterized by acute onset of
fever followed by jaundice within two weeks of onset of first
symptoms AND one of the following: 1) bleeding from the nose,
gums, GI tract or skin; or 2) death within 3 weeks of illness
onset.
- Laboratory criteria:
Isolation of yellow fever virus or
presence of yellow fever specific IgM or a four-fold or
greater rise in serum IgG levels (acute or 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 meets that
clinical description or where other causes
of acute fever/jaundice are excluded in the icteric
syndrome surveillance.
- Confirmed: A suspected case that is
laboratory confirmed or epidemologically linked to a
laboratory-confirmed case or outbreak.
RECOMMENDED SURVEILLANCE MEASURES
- The surveillance of icteric syndrome is a
method to apply a more sensitive case definition, and
then exclude individuals based upon laboratory testing.
Icteric syndrome includes any individual living in, or
recently traveling to, a yellow fever endemic zone who
develops sudden onset of fever and jaundice. If an
appropriate blood sample tests negative for hepatitis,
malaria, leptosporosis, and Dengue Hemorrhagic Fever, the
sample should be tested for yellow fever.
- Routine weekly/monthly reporting of
aggregated data on suspected and confirmed cases from
municipalities to central level. Zero reporting should be
required and periodically validated.
- All suspected cases and outbreaks should
be investigated immediately and laboratory confirmed;
during an outbreak, case-based data should be collected
- Case-based surveillance should be
implemented in all yellow fever enzootic countries.
Specimens should be collected to confirm an epidemic as
rapidly as possible. Then priority should be placed on
collecting specimens from new or neighboring areas.
- Coordination with the EPI country program
and WHO is essential in response to any outbreak of
disease.
- Feedback every month to all participants
of the surveillance system is recommended.
RECOMMENDED MINIMUM DATA ELEMENTS
Aggregated data (monthly): (i)
number of cases by month and geographic area (ii) yellow fever
vaccine coverage by age group.
Case-based data: (i) unique
identifier (ii) date of birth (iii) geographic location (iv)
laboratory results (vii) date of each yellow fever shot received
(viii) outcome (alive, dead, unknown) (ix) case classification
(suspected, confirmed, discarded) and (x) date of dead.
PRINCIPAL USES OF DATA FOR
DECISION-MAKING
- Investigate suspect cases and collect
laboratory specimens to confirm an outbreak and mobilize
emergency immunization activities through coordination of
a yellow fever epidemic committee.
- Monitor yellow fever vaccine coverage by
geographic region to assess progress towards outbreak
prevention and identify areas of poor performance so that
corrective actions can be taken.
- Monitor incidence rate to assess impact of
control efforts.
- Determine age-specific incidence rate, and
incidence rate by geographical area to identify risk
groups.
SURVEILLANCE INDICATORS
- % of reporting sites that report each
month (target 90%)
- Percent of all suspect cases for which
specimens were collected (target 80%)
- For IgM test: Laboratory results sent <
3 days of receipt of acute blood specimen (target 80%)
- For virus isolation: Laboratory results
sent < 21 days of receipt of acute blood specimen
(target 80%)
Source PAHO-WHO
