Highly sensitive point-of-care diagnostic tools for detection of all human malaria species are needed to make MSAT an effective strategy in settings where malaria elimination programs are in the pre-elimination phase.

Background: Reactive case detection (RCD) is a commonly used strategy for malaria surveillance and response in elimination settings. Many approaches to RCD assume detectable infections are clustered within and around homes of passively detected cases (index households), which has been evaluated in a number of settings with disparate results. Methods: Household questionnaires and diagnostic testing were conducted following RCD investigations in Zanzibar, Tanzania, including the index household and up to 9 additional neighboring households. Results: Of 12,487 participants tested by malaria rapid diagnostic test (RDT), 3·2% of those residing in index households and 0·4% of those residing in non-index households tested positive (OR = 8·4; 95%CI: 5·7, 12·5). Of 6,281 participants tested by quantitative polymerase chain reaction (qPCR), 8·4% of those residing in index households and 1·3% of those residing in non-index households tested positive (OR = 7·1; 95%CI: 6·1, 10·9). Within households of index cases defined as imported, odds of qPCR-positivity amongst members reporting recent travel were 1·4 times higher than among those without travel history (95%CI: 0·2, 4·4). Amongst non-index households, odds of qPCR-detectable infection were no different between households located within 50 m of the index household as compared with those located farther away (OR = 0·8, 95%CI: 0·5, 1·4). Sensitivity of RDT to detect qPCR-detectable infections was 34% (95%CI: 26·4, 42·3). Conclusions: Malaria prevalence in index households in Zanzibar is much higher than in non-index households, in which prevalence is very low. Travelers represent a high-risk population. Low sensitivity of RDTs due to a high prevalence of low-density infections results in an RCD system missing a large proportion of the parasite reservoir.

Since 2012, the Zanzibar Malaria Elimination Program has been implementing reactive case detection (RACD). Health facility (HF) staff send individual malaria case notifications by using mobile phones, triggering a review of HF records and malaria testing and treatment at the household level by a district malaria surveillance officer. We assessed the completeness and timeliness of this system, from case notification to household-level response. We reviewed two years (2015-2016) of primary register information in 40 randomly selected HFs on Zanzibar's two islands Unguja and Pemba and database records of case notifications from all registered HFs for the period 2013-16. The operational coverage of the system was calculated as proportion of HF-registered cases that were successfully reviewed and followed up at their household. Timeliness was defined as completion of each step within 1 day. Public HFs notified almost all registered cases (91% in Unguja and 87% in Pemba), and 74% of cases registered at public HFs were successfully followed up at their household in Unguja and 79% in Pemba. Timely operational coverage (defined as each step, diagnosis to notification, notification to review, and review to household-level response, completed within 1 day) was achieved for only 25% of registered cases in Unguja and 30% in Pemba. Records and data from private HFs on Unguja indicated poor notification performance in the private sector. Although the RACD system in Zanzibar achieved high operational coverage, timeliness was suboptimal. Patients diagnosed with malaria at private HFs and hospitals appeared to be largely missed by the RACD system.