MALARIA ELIMINATION IN ZANZIBAR - Soper Strategies

SURVEILLANCE AND RESPONSE FOR MALARIA
ELIMINATION
OVERVIEW AND OBJECTIVES
As discussed in Chapter 1, elimination is fragile, and malaria
will definitely resurge on Zanzibar if necessary interventions are
not put in place and maintained. The most important of those
interventions, both for achieving elimination and preventing
reintroduction, is a robust surveillance system. If new imported
malaria cases and emerging outbreaks are rapidly detected and
reported, the program will be able to mount an appropriate
response and prevent large-scale resurgence. Without these
“eyes and ears,” the program will be largely powerless to stop
imported malaria cases from leading to the reestablishment of
local transmission and potentially devastating epidemics. Table
1 gives an overview of how surveillance should evolve if Zanzibar
pursues an elimination program.
TABLE 1: SURVEILLANCE IN THE DIFFERENT STAGES OF MALARIA
CONTROL AND ELIMINATION
Control Pre-
elimination
Goal Reduce
morbidity and
mortality
Objective Reduce
transmission
intensity
Halt local
transmission
Reduce
onward
transmission
from existing
cases
Elimination Maintenance
Halt local
transmission
Reduce onward
transmission
from existing
cases
Unit Country Foci Foci/case (local
and imported)
Methods/
Data
Objective
of data
collection
Surveys/
Health
facility data
(monthly)
M&E (impact
of control
measures)
(Adapted from WHO, 2007)
Surveys/
Health
facility data
(weekly)/Case
notification
Improved
surveillance
to avoid
outbreaks
Sero-prevalence
surveys/Case
notifications/
Active and
passive case
detection
Detection and
response to all
new cases to
avoid onward
transmission
Prevent
re-introduction
Reduce onward
transmission
from imported
cases
Case
(imported)
Sero-prevalence
surveys/Active
and passive case
detection
Vigilance. All
new cases
(imported or
local) detected
and addressed
to prevent
resurgence
The surveillance system must be able to rapidly detect, investigate
and respond to any (abnormal) increase in the number of malaria
cases. The main differences when moving towards elimination
are that the surveillance system will not only have to detect
symptomatic cases but asymptomatic ones as well and that one
single case-not an increase in cases-will require an immediate
response. Mapping all identified cases using GIS technology
will enable the program to identify and appropriately address
potential or new pockets of malaria transmission, also called
“foci”. A transmission focus is defined as “a circumscribed locality
situated in a currently or formerly malarious area and containing
continuous or intermittent epidemiological factors necessary for
malaria transmission” (WHO EMRO, 2007). In Zanzibar, a
focus could be a village, shehia, town, or district.
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A strong surveillance system is also needed to eventually confirm
and receive certification for the achievement of elimination
(Yekutiel, 1980). However, the WHO only certifies countries,
and it is unlikely that Zanzibar, which is part of the United
Republic of Tanzania, will be eligible for certification when they
have achieved elimination (WHO, 2007).
During control, programs are focused on population-wide
interventions and are therefore interested in broad measures
of morbidity that can be captured monthly or sometimes even
less frequently in a limited geographical area (sentinel sites). An
elimination program, however, must eventually be interested in
every individual case and needs a system sensitive and efficient
enough to detect and report those cases within hours or days
throughout the country.
As a program moves to elimination, it must invest heavily in its
surveillance system to ensure that it meets the necessary standard
of speed and sensitivity. A surveillance system is comprised of
three core components:
�� Collection of case data through active and passive detection
methods;
�� Analysis and interpretation of data including case
investigation; and
�� Appropriate response, including radical treatment and
targeting of foci.
When moving towards elimination, it is not only important
to detect symptomatic cases to ensure prompt and effective
treatment but also to detect cases that do not necessarily
present with symptoms, as these can also be a source of onward
transmission. The malaria case definition during an elimination
program should therefore shift to: “a person in whom, regardless
of any symptoms, malaria parasites have been confirmed by
quality-controlled laboratory diagnosis” (WHO, 2007). In
addition, when the malaria endemicity becomes very low,
malaria transmission becomes more heterogeneously distributed
with foci erupting in apparently random places. The implication
of this new case definition and the heterogeneous behavior of
malaria transmission are discussed below.
If Zanzibar wants to eliminate malaria, they will need to
progressively strengthen and adapt their current surveillance
systems to meet the targets outlined in the table above. With
the support of the President’s Malaria Initiative, Zanzibar has
recently taken important steps in that direction by improving its
passive surveillance system. Much greater effort will be required
in this area if the country does pursue elimination. Not only
will the current passive surveillance system need to be further
improved, but also a complementary active case detection system
will have to be created. The specific surveillance methods needed
are further described below.