MALARIA ELIMINATION IN ZANZIBAR - Soper Strategies

most secondary cases but would occasionally lead to a small
outbreak. We calculated the operational requirements for 100
households to be screened as any number lower than 100 can then
be considered to be within an operationally feasible range. The
operational requirements can be calculated as illustrated in Table 2.
TABLE 2: OPERATIONAL REQUIREMENTS FOR RACD FOR DIFFERENT
LEVELS OF IMPORTATION RISK ONCE ELIMINATION IS ACHIEVED
(ESTIMATES BASED ON 2020 POPULATION EXTRAPOLATIONS)
# Cases detected (PCD
+ ACD)
# Households to be
screened (100/detected
case)
# HH/district/month
(# to be screened / 01
districts/ 12 months)
Estimated number of
teams per district
2/1000/year (prevention
at >75% effective
coverage)
1.6 per 1000 people per
year 2,781 cases
278,089 1,275,879
2,317 10,632
5 teams (24 working
days per month doing
20 HH per day per
team)
8/1000/year (prevention
at >75% effective
coverage)
7.35 per 1000 people
12,759 cases
22 teams (24 working
days per month doing
20 HH per day per
team)
The estimates from Table 2 assume that only 50% of infections
are detected by the PCD system and the rest through RACD. It
is safe to assume that by 2020 PCD should be able to pick up
a higher proportion of infections thus reducing the proportion
RACD needs to pick up, making the estimates in the table very
conservative. Nevertheless, at lower ends of importation risk,
RACD will be challenging but seems operationally feasible even
if PCD only detects 50% of all infections.
If preventive measures would be scaled back completely, PCD
complemented by RACD alone cannot avoid outbreaks unless
the importation risk is significantly reduced. This can only be
achieved through pro-active case detection methods such as
border screening or screening of high-risk groups (see below).
Given the encouraging results from the simulations, we
recommend that Zanzibar begin developing and implementing
RACD early in their elimination program. As discussed below
and in the section “From ZMCP to ZMEP,” this will require
additional human resources both at the central and the district
level, the necessary diagnostics tests for screening (RDTs), and
standardized reporting tools and systems. As discussed in detail
below, the area to be screening will depend on whether the initial
investigation suggests that the identified case is most likely a
locally acquired infection (no travel history) or an imported case
(recent travel to a malaria endemic country/region).
Pro-Active Case Detection (PACD)
Pro-active case detection is the screening of an area or group of
people considered to be at high risk for malaria transmission,
even if no cases have been identified recently. This screening can
be done either continuously or during certain high-risk seasons
(defined by the malaria transmission and/or human migration
patterns). Potential groups/areas targeted by this approach might
include:
2 | Operational Feasibility
�� Areas with a high entomological inoculation rate (EIR) and a
high population density;
�� Seasonal migrant workers;
�� Travelers from (high) endemic areas (border screening).
The surveillance simulation indicates that prevention can
be scaled back if PCD detects 77% of all infections, RACD
screens around 100 households around every case detected, and
a combination of malaria control on the mainland and PACD
lowers the importation risk dramatically (see Table 3).
TABLE 3: REQUIREMENTS FOR PCD, RACD AND PACD TO AVOID RESUR-
GENCE WHEN PREVENTION (IRS/LLIN) IS SCALED-BACK
Passive Case Detection Pro-Active Case
Detection
!" 90% of infections
become symptomatic
!" 90% of all febrile
cases seek medical
care
!" The diagnostic test
used has sensitivity
of 95%
!" Testing and
treatment rates at
100%
77% of all infections
detected and treated
Although the estimates for RACD might seem operationally
feasible, achieving 77% passive case detection rates and
importation risk of 0.4/1000/year will be extremely challenging
and will depend on what will/can be achieved on the mainland. We
are therefore not in a position to make concrete recommendation
on PACD. Operational research needed to define high-risk areas/
groups is discussed in the Technical Feasibility Chapter. In the
short-term, PACD is therefore not yet recommended.
ANALYSIS AND RESPONSE
!" Importation risk
reduced from 2/1000/
year to 1/1000 per
year through control
measures on the
mainland
!" Border screening
and screening of high
risk groups detects
and treats 60% of
imported cases
Importation risk at
0.4/1000/year
Re-Active Case
Detection
!" PCD will detect
0.53/1000/ year
or 739 cases each
year (using 2020
population figures)
!" Detecting these
cases requires 73,900
House Holds to be
screened or 665 per
district per month
With a maximum
capacity of 20 HH/
day for 24 days/
month; 2 teams per
district are sufficient
The surveillance system is only as useful as the response it elicits.
As described above, strong surveillance enables the program to
identify and target its interventions at residual and potential foci.
To do so, the program must first understand and interpret the
often complex data gathered by the system. This is done through:
�� Epidemiological analysis of the data gathered by the MEEDS,
from case investigations and re-active case detection
(screening) around the index case;
�� Analysis of entomological data collected from targeted areas
(see below); and
�� Geo-statistical analysis using geo-referenced data on malaria
cases, vector breeding sites, remotely sensed data and climate/
meteorological data.
The results of the analysis not only define the required response,
but also allow for the identification of high-risk areas. Such
identification can permit preemptive action directed at potential
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