In this analysis of published studies on RACD in the GMS, we found an overall yield from microscopy and/or RDT of roughly one case detected per 200 contacts tested. The yield from PCR was four times higher than microscopy and/or RDT but PCR is generally not used for screening because it is expensive, time- and labour-intensive, and requires advanced laboratory capacity. Critically, the results from PCR testing of samples are not immediately available, delaying the treatment of infected contacts. To achieve the highest impact infected contacts should be diagnosed with an appropriate point of care test and treated immediately.
Standard PCR, as used in the studies reported here, had higher yield than RDT, but has been estimated to miss about half of malaria positives, particularly low density infections . Hopes that “highly sensitive” RDTs could solve these diagnostic challenges turned out to be misplaced.  “Highly sensitive” in context of RDTs is rather a misnomer because the additional yield compared to standard RDTs is minimal but the price is roughly twice that of standard RDTs.
Further restricting the yield of the RACD reported here is the primary focus on household contacts, an approach which was found to be effective in China where malaria transmission occurs within the household . This approach may be less appropriate in the GMS where the large majority of infections occurs outdoors, in farms and forested areas. The people at risk are, therefore, those who work in the same location as the index case and not necessarily share the same household . Only two studies in this review compared target groups and found higher yields from screening co-workers and co-travellers than household contacts [11, 12].
This review has several limitations. There were only a few published studies reporting the yield of RACD. Secondly, the studies were done in only some areas of the GMS. The majority of data for this review come from Cambodia with some additional data from China and Thailand. A more complete picture would require the inclusion of more data from Laos and Vietnam. Thirdly, the studies incorporated a wide variety of public health and research methodologies in the tracing and confirmation of contacts, which may question the value of aggregating these different datasets. In the absence of other published sources of information, this is the currently best available method to describe the yield of RACD in the GMS. Assessments of routinely collected data from the GMS malaria control programmes would be important to determine the actual yield of RACD. This review highlights the need for more standardized protocols in RACD, so that results can be compared by location and over time.
The implications for public health are multi-fold. If investigators have to test 200 people to detect a single case, their enthusiasm for RACD is likely to wane quickly. Perhaps it is more promising under the given circumstances to treat contacts presumptively with appropriate schizontocidal anti-malarials, i.e. not including the use of 8-aminoquinolines for radical cure of vivax malaria. Presumptive treatment avoids not only the costs for diagnostic tests which can be more expensive than a course of anti-malarials, but also the risk of missing cases due to the inadequate sensitivity of tests. Such presumptive treatment should probably consist of a full curative regimen using a drug combination to be determined in discussion with each National Malaria Control Program. The disadvantages of presumptive treatment is the reluctance of many contacts to receive treatment in the absence of testing and the increase in anti-malarial consumption leading to an increase in drug pressure. Alternatively, locally-appropriate evidence-based targeting of RACD, such as including household members in villages close to the forest but focusing on occupational contacts who share exposure in time and space with the index case in other areas.
Results from screening of contacts may be needed by national programmes to track progress towards malaria elimination and to support certification of elimination in the longer term. Presumptive treatment of contacts could still be carried-out but with the prior collection of dried blood on filter paper, labelled with the date and location. The dried blood smears could be transported centrally and batched-tested by PCR. The deferred PCR results would be used for identifying areas of continued transmission over time. Collection and PCR testing of dried blood smears will only be feasible in countries with available logistics and funds.