—from Epidemiological Bulletin,
Vol. 24 No. 2, June 2003—
Case Definition:
Ebola-Marburg viral diseases
Rationale for surveillance
Ebola haemorrhagic fever is a rare but severe disease occurring primarily in
areas of the African rain forest. The disease is characterized by person-to-person
transmission through close contact with patients, dead bodies or infected body
fluids. Epidemics of the disease can be dramatically amplified in health care
centers with poor hygiene standards; the attendant potential for explosive nosocomial
infection constitutes the main threat to public health posed by the disease.
Surveillance is aimed at early detection of cases in order to avoid epidemics
and possible international spread of the disease.
Marburg virus infections are extremely rare. They appear to be
similar to Ebola hemorrhagic fever and recommendations for both viral infections
are the same.
Recommended case definition
Clinical description
Ebola hemorrhagic fever begins with acute fever, diarrhea that can be bloody
(referred to as “diarrhée rouge” in francophone Africa), and
vomiting. Headache, nausea, and abdominal pain are common. Conjunctival injection,
dysphagia, and hemorrhagic symptoms such as nosebleeds, bleeding gums, vomiting
of blood, blood in stools, purpura may further develop. Some patients may also
show a maculopapular rash on the trunk. Dehydration and significant wasting
occur as the disease progresses. At a later stage, there is frequent involvement
of the central nervous system, manifested by somnolence, delirium, or coma.
The case-fatality rate ranges from 50% to 90%.
Laboratory criteria for diagnosis
Supportive
– Positive serology (ELISA for IgG and/or IgM), or
Confirmatory
– Positive virus isolation (only in a laboratory of biosafety level
4) or
– Positive skin biopsy (immunohistochemistry) or
– Positive PCR
Case classification
Suspected: A case that is compatible with the clinical description.
Probable (in epidemic situation):
– Any person having had contact with a clinical case and presenting with
acute fever, or
– Any person presenting with acute fever and 3 of the following symptoms:
headache, vomiting / nausea, loss of appetite, diarrhea, intense fatigue, abdominal
pain, general or articular pain, difficulty in swallowing, difficulty in breathing,
hiccoughs, or
– Any unexplained death.
Confirmed: Any suspected or probable case that is
laboratory-confirmed.
Contact (in epidemic situation):
An asymptomatic person having had physical contact within the past 21 days with
a confirmed or probable case or his/her body fluids (e.g., care for patient,
participation in burial ceremony, handling of potentially infected laboratory
specimens).
In epidemic situations and after laboratory confirmation of
a few initial cases, there is no need for individual laboratory confirmation
and the use of “suspected or probable” case classifications is sufficient
for surveillance and control purposes.
Recommended types of surveillance
In endemic areas and in the absence of an epidemic:
Immediate reporting of suspected cases from the periphery to intermediate and
central levels to ensure rapid investigation and laboratory confirmation.
Note: Routine surveillance of Ebola haemorrhagic fever
must be integrated with routine surveillance for other viral haemorrhagic fevers
(e.g., Crimean-Congo fever, Lassa fever, Rift Valley fever, yellow fever).
In epidemic situations:
– Intensified surveillance and active finding of all suspected and
probable cases for immediate isolation, and of all contact subjects for daily
medical follow-up.
– The surveillance area should be monitored for a duration corresponding
to 2 estimated incubation periods after the date of death or hospital discharge
of the last case.
– A rumour registry should be established to create a systematic registration
of rumours of cases reported by the population.
– A single source of official information is essential to ensure coherence
and avoid confusion in the public.
Recommended minimum data elements
Case-based data for reporting and investigation
– Case classification (suspected/probable/confirmed).
– Unique identifier, name, age, sex.
– Geographical information, name of head of family, name of father (if
child).
– Profession, place of work.
– Date of onset of fever, symptoms, signs.
– Hospitalization, including date.
– Death including date.
– Contact with previous case, including date.
– Nature and date of clinical samples taken for laboratory investigation
(if any).
Aggregated data for reporting
– Number of cases (suspected/probable/confirmed) by age, sex.
– Number of deaths.
Recommended data analyses, presentation, reports (epidemic
situations)
An epidemiological bulletin should be sent daily to local health authorities
and to WHO headquarters. It should include the following information:
Cases:
– Total cumulative number of cases
– Total cumulative number of deaths
– Current number of patients
– Current number of hospitalized patients
– Date of last identified case
– Date of death or hospital discharge of the last reported case
Breakdown by sex and age group can also be provided
Contacts:
– Current number of contacts requiring follow up
– Current number of contacts under proper follow-up
Breakdown by sex and age group can also be provided
When possible, the geographic distribution of cases and contacts
should be provided, as well as a simple epidemic curve.
Case-fatality rates, attack rates, and age-specific attack rates
can be calculated for epidemiological assessment.
A more detailed report summarizing events and data should be produced
weekly and a complete report should be available at the end of the epidemic.
Principal uses of data for decision-making
Routine surveillance data
– Detect an isolated case or an outbreak and immediately take appropriate
measures to avoid an epidemic.
Active case finding and contact tracing during outbreaks are
essential for control
– Identify all cases and contacts
– Assess and monitor the spread of an outbreak
– Evaluate control measures
– Provide a basis for research (epidemiological data, clinical specimens)
Special aspects
Since extreme biohazard is associated with sampling, transportation and
laboratory investigation, strictly applied biosafety procedures and appropriate
isolation of patients are essential.
All known Ebola strains from Africa produce disease in humans;
one Ebola strain from the Philippines (Reston) has infected humans without producing
disease.
Source: “WHO Recommended Surveillance Standards, Second
edition, October 1999”, WHO/CDS/CSR/ISR/99.2
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Epidemiological Bulletin, Vol. 24 No. 2, June
2003
